News From the Kamat Lab



Friday, October 31, 2014Posted by Jeff Christians

Kamat Lab Papers Make Most Read Lists

The past year has been an exciting and productive time in the Kamat Lab! Below are 7 articles that currently feature among the Most Read Articles in their respective journals over the past 12 months. Congratulations to all of the various authors who have contributed to this exciting work!

467. Band Filling with Free Charge Carriers in Organometal Halide Perovskites
Manser, J. S.; Kamat, P. V. Nat. Photon. 2014, 8, 737–743.

458. Quantum Dot Solar Cells. Hole Transfer as a Limiting Factor in Boosting Photoconversion Efficiency
Kamat, P. V.; Christians, J. A.; Radich, J. G. Langmuir 30 (20), 5716-5725 (Feature Article).

454. Recent Advances in Quantum Dot Surface Chemistry
Hines, D. A.; Kamat, P. V. ACS Appl. Mater. Interfaces 2014, 6 (5), 3041–3057.

449. An Inorganic Hole Conductor for Organo-Lead Halide Perovskite Solar Cells. Improved Hole Conductivity with Copper Iodide
Christians, J. A.; Fung, R. C. A.; Kamat, P. V. J. Am. Chem. Soc. 2014, 136 (2), 758-764.

438. Quantum Dot Solar Cells. The Next Big Thing in Photovoltaics.
Kamat, P. V. J. Phys. Chem. Lett. 2013, 4, 908–918.

374. Quantum Dot Solar Cells. Semiconductor Nanocrystals as Light Harvestors - Centennial Feature Article
Kamat, P. V. J. Phys. Chem. C 2008, 112, 18737-18753 . NDRL 4770

353. Meeting the Clean Energy Demand: Nanostructure Architectures for Solar Energy Conversion.
Kamat, P. V. J. Phys. Chem. C 2007, 111, 2834-2860. (Feature Article in February 22 2007 issue) NDRL 4697

All Publications

Tuesday, October 28, 2014Posted by Jeff Christians

Editorial: Mastering the Art of Scientific Publication

"As new researchers generate their first results, they face the challenge of mastering the art of scientific publication in order to present their results and to draw attention to their new scientific findings. Whether or not we want to describe science in such terms, scientific publishing is competitive in nature, and thus younger scientists must vie with their more experienced peers for recognition. While the electronic age has made the publication process easier and quicker, optimizing the structure of a scientific paper requires a certain degree of skill and proficiency.(1) ACS Publications has been actively engaged in disseminating the basics of publication through Publication 101 videos and editorials and, in continuation of this spirit, we have assembled this virtual issue (http://pubs.acs.org/page/vi/art_of_scientific_publication.html). This issue draws together, in one place, these editorials that summarize the key steps involved in writing an effective paper, journal submission, review processes, and postpublication efforts. The twenty editorials assembled for this virtual issue provide further details on each of these topics. These topics may also be useful as part of the curriculum for the training of students and young researchers in any academic department."

View Editorial

Monday, September 15, 2014Posted by Jeff Christians

Sachi to Los Alamos

Sachidananda Krishnamurthy

Join us in congratulating Dr. Sachidananda Krishnamurthy on a great postdoc position at both UT Dallas and Los Alamos National Laboratory! Sachi will be working under the mentorship of Dr. Jennifer Hollingsworth at Los Alamos and Dr. Anton Malko and UT Dallas. He will be working on hybrid near IR QDSCs. Congratulations Sachi!




Thursday, August 21, 2014Posted by Jeff Christians

Editorail: What's in a Name?

"What is the first thing that draws the attention of any reader to look into a scientific paper? Naturally, it is the title. The title is something that stays around for the life of a paper, similar to an inherited name. Given the volume of papers being published in any given discipline in recent years, one can easily miss reading a paper if the article title listed in a journal's table of contents or in database search results fails to draw the attention of a potential reader. Is it not worth an author's time to come up with an effective and attractive title?"

View Editorial

Wednesday, August 20, 2014Posted by Jeff Christians

Editorail: Reporting on Heterogeneous Photocatalysis

This editorial written for ACS Applied Materials and Interfaces looks into the best practices for reporting on hetergeneous photocatalysis. It includes tips for making measurements as well as proper reporting of values and things to watch out for in the literature.

Best Practices for Reporting on Heterogeneous Photocatalysis

Heterogeneous photocatalysis is of broad interest in materials chemistry and materials science, particularly with the rapid growth of research attention being directed toward energy-related applications, pollution mitigation, and other related areas of environmental impact.(1) A literature survey reveals more than 9000 papers with the word photocatalyst or photocatalysis in the title published during the last ten years (Source: Web of Science, July 3, 2014), with the number of papers published each year increasing significantly since 2005. The materials and physical chemistry journals of the American Chemical Society receive a significant number of papers in the area of photocatalysis.

View Editorial

Wednesday, August 20, 2014Posted by Jeff Christians

Catalytic Reduction of CO2 with TiO2

Read the latest paper from the Kamat Lab!

The Origin of Catalytic Effect in the Reduction of CO2 at Nanostructured TiO2 Films

The Origin of Catalytic Effect in the Reduction of CO2 at Nanostructured TiO2 Films

Abstract: Electrocatalytic activity of mesoscopic TiO2 films towards the reduction of CO2 is probed by depositing a nanostructured film on a glassy carbon electrode. The one-electron reduction of CO2 in acetonitrile seen at an onset potential of -1.1 V (vs. NHE) is ~0.5 V lower than the one observed with a glassy carbon electrode. The electrocatalytic role of TiO2 is elucidated through spectroelectrochemistry and product analysis. Ti3+ species formed when TiO2 film is subjected to negative potentials have been identified as active reduction sites. Binding of CO2 to catalytically active Ti3+ followed by the electron transfer facilitates the initial one-electron reduction process. Methanol was the primary product when the reduction was carried out in wet acetonitrile.

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Wednesday, August 13, 2014Posted by Jeff Christians

PhysOrg: Band Filling in Perovskite

Band filling with free charge carriers in organometal halide perovskites

PhysOrg: A new paper by University of Notre Dame researchers describes their investigations of the fundamental optical properties of a new class of semiconducting materials known as organic-inorganic "hybrid" perovskites.

The research was conducted at the Notre Dame Radiation Laboratory by Joseph Manser, a doctoral student in chemical and biomolecular engineering, under the direction of Prashant Kamat, Rev. John A. Zahm Professor of Science. The findings appear in a paper in the August 10 edition of the journal Nature Photonics.

Article continued on PhysOrg

View Article

Wednesday, August 13, 2014Posted by Jeff Christians

C&EN: Graphene Surprises By Decomposing

Graphene surprises by decomposing

C&EN: Graphene's hallmark chemical stability has made this ultrathin carbon network an ideal support material in catalysis and energy studies. But that inertness is now being called into question by an investigation showing that the material can decompose when used in common applications (Chem. Mater. 2014, DOI: 10.1021/cm5026552).

Water-dispersible forms of graphene are easy to make and easy to handle via simple wet-chemistry methods. Large numbers of researchers use the materials to support nanoparticle catalysts for use in environmental remediation, solar cells, and fuel cells.

Article continued on C&EN

View Article

Monday, August 11, 2014Posted by Jeff Christians

Band Filling in Perovskite

Read the latest paper from the Kamat Lab!

Band filling with free charge carriers in organometal halide perovskites

Band filling with free charge carriers in organometal halide perovskites

Abstract: The unique and promising properties of semiconducting organometal halide perovskites have brought these materials to the forefront of solar energy research. Here, we present new insights into the excited-state properties of CH3>NH3PbI3 thin films through femtosecond transient absorption spectroscopy measurements. The photoinduced bleach recovery at 760 nm reveals that band-edge recombination follows second-order kinetics, indicating that the dominant relaxation pathway is via recombination of free electrons and holes. Additionally, charge accumulation in the perovskite films leads to an increase in the intrinsic bandgap that follows the Burstein–Moss band filling model. Both the recombination mechanism and the band-edge shift are studied as a function of the photogenerated carrier density and serve to elucidate the behaviour of charge carriers in hybrid perovskites. These results offer insights into the intrinsic photophysics of semiconducting organometal halide perovskites with direct implications for photovoltaic and optoelectronic applications.

View Paper

Wednesday, July 23, 2014Posted by Jeff Christians

Is Graphene Stable for Photocatalysis?

Read the latest paper from the Kamat Lab!

Is Graphene a Stable Platform for Photocatalysis? Mineralization of Reduced Graphene Oxide with UV-Irradiated TiO2 Nanoparticles

Is Graphene Stable for Photocatalysis

Abstract: The recent thrust in utilizing reduced graphene oxide (RGO) as a support for nanostructured catalyst particles has led to the claims of improved efficiency in solar cells, fuel cells, and photocatalytic degradation of pollutants. Specifically, the robust TiO2 system is often coupled with RGO to improve charge separation and facilitate redox reactions. Here we probe the stability of RGO in the presence of UV-excited TiO2 in aqueous media and establish its reactivity towards OH radicals, a primary oxidant generated at the TiO2 surface. By probing changes in absorption, morphology and total organic carbon content (TOC) we conclusively demonstrate the vulnerability of RGO towards OH attack and raise the concern of its use in many applications where OH are likely to be formed. On the other hand, the OH radical-mediated mineralization could also enable new approaches in tackling environmental remediation of nanocarbons such as RGO, carbon nanotubes, and fullerenes.

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Wednesday, July 23, 2014Posted by Jeff Christians

Size Dependent Excited State of Au Clusters

Read the latest paper from the Kamat Lab!

Size Dependent Excited State Behavior of Glutathione Capped Gold Clusters and Their Light Harvesting Capacity

Size Dependent Excited State of Au Clusters

Abstract: Glutathione protected gold clusters exhibit size dependent excited state and electron transfer properties. Larger size clusters (e.g., Au25GSH18) with core-metal atoms display rapid (<1 ps) as well as slower relaxation (~200 ns) while homoleptic clusters (e.g., Au10-12GSH10-12) exhibit only slower relaxation. These decay components have been identified as metal-metal transition and ligand-to-metal charge transfer respectively. The short lifetime relaxation component becomes less dominant as the size of the gold cluster decreases. The long-lived excited state and ability to participate in electron transfer are integral for these clusters to serve as light harvesting antennae. A strong correlation between the ligand-to-metal charge-transfer excited state lifetime and photocatalytic activity was evidenced from the electron transfer to methyl viologen. The photoactivity of these metal clusters show increasing photocatalytic reduction yield (0.05 - 0.14) with decreasing cluster size, Au25 < Au18 < Au15 < Au10-12. Gold clusters, Au18GSH14, were found to have the highest potential as a photosensitizer based on the quantum yield of electron transfer and good visible light absorption properties.

View Paper

Wednesday, July 23, 2014Posted by Jeff Christians

Förster versus Dexter

Read the latest paper from the Kamat Lab!

Size Dependent Energy Transfer Pathways in CdSe Quantum Dot-Squaraine Light Harvesting Assemblies: Förster versus Dexter

Förster versus Dexter

Abstract: Energy transfer coupled with electron transfer is a convenient approach to mimic photosynthesis in light energy conversion. Better understanding of mechanistic details of energy transfer processes is important to enhance the performance of dye or quantum dot sensitized solar cells. Energy transfer through both long range dipole based Förster Resonance Energy Transfer (FRET), and short range Dexter Energy Transfer (DET) mechanisms have been identified to occur between CdSe quantum dots (QDs) linked to a red-infrared absorbing squaraine dye through a short thiol functional group (SQSH). Solutions of SQSH linked to CdSe were investigated through steady-state and time resolved spectroscopy experiments to explore both mechanisms. Photoluminescence studies revealed that smaller QDs had higher energy transfer efficiencies than predicted by FRET, and femtosecond transient absorption experiments revealed faster energy transfer rates in smaller donor QD sizes. These findings supported A DET process dominating at small donor sizes. The presence of both processes illustrates multiple strategies for utilizing energy transfer in light harvesting assemblies and the required considerations in device design to maximize energy transfer gains through either mechanism.

View Paper

Thursday, July 17, 2014Posted by Jeff Christians

Why Did You Accept My Paper?

This editorial written by the J. Phys. Chem. Lett. editors appears in today's issue. It highlights manuscript attributes contributing to favorable editorial decisions.

Why Did You Accept My Paper?

This is one question that we never hear from our authors. Authors whose papers get accepted by the editor cherish their publication success, whereas authors whose papers were not accepted may in many instances put the blame squarely on the review process itself. From the author's perspective, the paper he/she just submitted consists of the best scientific results from his/her laboratory and hence deserves publication regardless of the quality of presentation. Editors and reviewers evaluate the papers from the journal reader's viewpoint. Essential factors in drawing a reader's attention to a particular paper include a broad perspective, a good fit with the journal scope, and clear presentation of new scientific findings. Editors and reviewers also check to see whether the paper meets the journal's submission criteria. Those authors who take these aspects into consideration while composing their manuscripts see a significantly higher success rate of acceptance.

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Wednesday, July 10, 2014Posted by Jeff Christians

They Said it Couldn't be Done

Rad Lab Lab Rats Softball Team

Sometimes softball can be a metaphor for life. You can't let the fact that half your team doesn't know the difference between left field and right field stop you, you just have to get back up and keep swinging.

The doubters were proven wrong, the impossible was accomplished, the Lab Rats won a softball game! Some would point out that it took into our third season to get our first win, but I would point out that we actually had a win two years ago when the other team forfeited, so the thrill of victory is not totally unfamiliar territory. While our offense kept us competitive in our first game, it was our stifling defense that helped us prevail to our first win of the season ever. We held the MBA team to just 1 run in a game that stretched the full 7 innings. The tone was set in the first inning when Doug unleashed 100% power and hit a huge home run that scored two and put us up for good. The only hiccup was when Jay thought he could be like Doug and ended up getting out after being thrown into a pickle between third and home. Nevertheless, the final score of 6-1 smelled of glory and tasted of victory! If we win our next game we make the playoffs!

View Pictures

Tuesday, July 1, 2014Posted by Jeff Christians

Opening Day at the Ballpark

Rad Lab Lab Rats Softball Team

The annual intramural softball season started up this week after the first game was rained out last week, and the Rad Lab Lab Rats walked onto the field to face the AME Bombers with fresh legs after taking the season off last year. Stepping up to the plate, we shook off the rust and jumped to an early 6-0 lead with some great (for us at least) hitting. Even Danilo, who was unsure whether the batter or pitcher was supposed to run after a hit, had a nice double! Then we took the field. Our defense is porous at best and a sieve at worst, and while I wouldn't say this was our worst outing, we quickly let the Bombers back into the game to tie it 6-6 after one. Danilo's play at second base to end the second inning was probably the highlight of the game. With two outs a hard grounder was hit just right of second base. Danilo ran over, reached out his glove and snagged the ball as it went past, and then, carried by his momentum, spun in a full circle before tossing the ball to Joe at second and getting the force out. Ultimately though, fatigue set in and the Lab Rats were not able to hold off the steady attack of the Bombers, eventually falling 16-11 in four innings. It was tough to start off the year with a loss but we will be back on the field next week hungry for our first win of the year!

Unfortunatly we forgot the camera today so there are no pictures but hopefully we will have some from our next game.

Thursday, June 19, 2014Posted by Jeff Christians

Editorial on Publication Figures

Read this editorial, entitled "Graphical Excellence," from Prashant, Journal of Physical Chemistry Letters Senior Editor Greg Hartland, and Editor-in-Chief George Schatz on the importance of high quality figures in conveying scientific information.

"It is the experience of every author that figures and illustrations in scientific papers are the gateway for effective communication of research findings to the scientific world. While the title and abstract of the paper draw the attention of any avid reader, the essence of the paper is captured by the figures and schemes. Well-drawn, scientifically correct figures make the first impression of the scientific findings. Yet, time and time again, we see poorly presented results, inaccuracy in plotted data, improperly defined axes, meaningless significant digits in axis scales, wrong or missing units, and undefined symbols or traces. Such inaccuracies can lead to reject recommendations from the editors and reviewers. We wonder why researchers who are passionate about communicating their findings, many times take little interest in effective presentation of their data."

View Paper

Wednesday, June 18, 2014Posted by Jeff Christians

Prashant Kamat - 2014 Highly Cited Researcher

Thomson Reuters Highly Cited Researchers 2014

Thomson Reuters compiled a list of approximately 3200 Highly Cited Researchers from around the world across 21 fields of the sciences and social sciences. Researchers were selected from each discipline who had published the most papers between 2001-2012 which ranked in the top 1% in citations relative to other papers published in the same field and in the same year. By this metric, three Notre Dame scientists made the list of Highly Cited Researchers, including Joan Brennecke (Chemistry), Bertrand Hochwald (Computer Science), and Prashant Kamat (Chemistry). Congratulations to all of the well deserving members of the 2014 Highly Cited Researchers list!

HCR 2014 Link

Monday, June 9, 2014Posted by Jeff Christians

Kamat Lab: Summer 2014

Prashant Kamat Lab Summer 2014

With school offically over and summer beginning in South Bend, the Kamat Lab is starting to take on its summer form. New students and scientists will be joining us this summer, and several people will be leaving. This summer we are saying goodbye to recent Ph. D. graduates Sachidananda Krishnamurthy and James Radich, as well as visiting scientist Dr. Santosh Haram. However, we are also welcoming Ivan Grigioni, Barry Reid, Pierre Miranda, Mark Wilson, and Abby Swint who will be working in the lab over the summer. We look forward to an enjoyable and productive summer!

Group Bios

Friday, June 6, 2014Posted by Jeff Christians

Sense and Shoot

Read the latest paper from the Kamat Lab!

Sense and Shoot: Simultaneous Detection and Degradation of Low Level Contaminants using Graphene Based Smart Material Assembly

Sense and shoot

Abstract: Smart material nanoassemblies that can simultaneously sense and shoot low level contaminants from air and water are important for overcoming the threat of hazardous chemicals. Graphene oxide (GO) sheets deposited on mesoscopic TiO2 films that underpin the deposition of Ag nanoparticles with UV-irradiation provide the foundation for the design of a smart material. The Ag particle size is readily controlled through precursor concentration and UV irradiation time. These semiconductor – graphene oxide – metal (SGM) films are SERS active and hence capable of sensing aromatic contaminants such as nitrobenzenethiol (NBT) in nanomolar range. Increased local concentration of organic molecule achieved through interaction with 2D carbon support (GO) facilitates low-level detection of contaminants. Upon UV irradiation of the NBT loaded SGM film, one can induce photocatalytic transformations. Thus, each component of the SGM film plays a pivotal role in aiding the detection and degradation of a contaminant dispersed in aqueous solutions. The advantage of using SGM films as multipurpose "detect and destroy" systems for nitroaromatic molecule is discussed.

View Paper

Thursday, May 29, 2014Posted by Jeff Christians

Langmuir - Cover Article

Langmuir - Cover Article

Congratulations to Jeff Christians on the cover art for the journal Langmuir! The cover art appeared in this month's issue of Langmuir to go along with Prashant, Jeff, and James's review article on hole transfer entitled, Quantum Dot Solar Cells: Hole Transfer as a Limiting Factor in Boosting the Photoconversion Efficiency.

About the Image: The artwork illustrates photoinduced charge-transfer processes in nanostructured solar cells. Top: Quantum dot solar cells (QDSCs). Center: Nanowire solar cells (NWSCs). Bottom: Extremely thin absorber (ETA) solar cells. Efficiencies greater than 5% have recently been achieved. The associated Invited Feature Article focuses on the limitations imposed by slow hole transfer and its role in the stability and power conversion efficiency of metal chalcogenide solar cells. Strategies to improve the rate of hole transfer through surface-modified redox relays offer new opportunities to overcome the hole-transfer limitation.

View Issue

Friday, May 23, 2014Posted by Jeff Christians

Switching the Reaction Course of CO2

Read the latest paper from the Kamat Lab!

Switching the Reaction Course of Electrochemical CO2 Reduction with Ionic Liquids

Switching the Reaction Course of Electrochemical CO<sub>2</sub> Reduction with Ionic Liquids

Abstract: The ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) offers new ways to modulate the electrochemical reduction of carbon dioxide. [emim][Tf2N], when present as the supporting electrolyte in acetonitrile, decreases the reduction overpotential at a Pb electrode by 0.18 V as compared to tetraethylammonium perchlorate as the supporting electrolyte. More interestingly, the ionic liquid shifts the reaction course during the electrochemical reduction of carbon dioxide by promoting the formation of carbon monoxide instead of oxalate anion. With increasing concentration of [emim][Tf2N], a carboxylate species with reduced CO2 covalently bonded to the imidazolium ring is formed along with carbon monoxide. The results highlight the catalytic effects of the medium in modulating the CO2 reduction products.

View Paper

Tuesday, April 29, 2014Posted by Jeff Christians

James to Auburn

James Radich accepts job at Auburn

Join us in congratulating Dr. James Radich as he will be starting a tenure track faculty position in the Department of Chemical Engineering at Auburn University. James has been a member of the Kamat group since he came to Notre Dame as a graduate student in 2009, receiving his Ph. D. in April, 2014, and will begin his new position at Auburn this June. As a faculty member, James will be seeking to develop a strong research program specializing in material science and electrochemistry. Congratulations James on this great accomplishment!

Monday, April 14, 2014Posted by Jeff Christians

KamatLab Youtube Channel

KamatLab Youtube Channel

Our group has published a variety of videos and webinar presentations through the website SlideShare. Because SlideShare is no longer supporting "Slidecasts" (Power Point presentations with audio) we have begun migrating all of our webinar presentations over to Youtube. You can now follow us on Youtube and see all of our latest updates and presentations, just click the link below!

Youtube Channel

Monday, April 14, 2014Posted by Jeff Christians

How Does a SILAR CdSe Film Grow?

Read the latest paper from the Kamat Lab!

How Does a SILAR CdSe Film Grow? Tuning the Deposition Steps to Suppress Interfacial Charge Recombination in Solar Cells

How Does a SILAR CdSe Film Grow? Tuning the Deposition Steps to Suppress Interfacial Charge Recombination in Solar Cells

Abstract: Successive Ionic Layer Adsorption and Reaction (SILAR) is a popular method of depositing the metal chalcogenide semiconductor layer on the mesoscopic metal oxide films for designing quantum dot sensitized solar cell (QDSSC) or Extremely Thin Absorber (ETA) solar cells. While this deposition method exhibits higher loading of light absorbing semiconductor layer than direct adsorption of pre-synthesized colloidal quantum dots, the chemical identity of these nanostructures and evolution of interfacial structure are poorly understood. We have now analyzed step-by-step SILAR deposition of CdSe films on mesoscopic TiO2 nanoparticle films using x-ray absorption near-edge structure analysis and probed the interfacial structure of these films. The film characteristics interestingly show dependence on the order in which the Cd and Se are deposited, and the CdSe-TiO2 interface is affected only during the first few cycles of deposition. Development of SeO2 passivation layer in the SILAR-prepared films to form TiO2/SeO2/CdSe junction facilitates an increase in photocurrents and power conversion efficiencies of quantum dot solar cells when these films were integrated as photoanodes in a photoelectrochemical solar cell.

View Paper

Monday, April 14, 2014Posted by Jeff Christians

Webinar - Band Gap Tunining in CdSeS NWs

CdSeS Nanowires. Compositionally Controlled Band Gap and Exciton Dynamics

Watch this ACS LiveSlides presentation on the synthesis of CdSeS nanowires. This webinar describes the tuning of the composition of the NWs by the ratio of Se:S precursor. This allows for the modulation of the NW band gap between 2.36 eV and 1.79 eV. The presentation is based off of the paper, recently published in Journal of Physical Chemistry Letters, entitled:

CdSeS Nanowires. Compositionally Controlled Band Gap and Exciton Dynamics.

Abstract: CdS, CdSe and ternary CdSexS(1-x) are some of the most widely studied II-VI semiconductors due to their wide range of applications and promising performance in numerous systems. One-dimensional semiconductor nanowires offer the ability to conduct charges efficiently along the length of the wire which has potential charge transport benefits compared to nanoparticles. Herein, we report a simple, inexpensive synthetic procedure for high quality CdSeS nanowires where the composition can be easily modulated from pure CdSe to pure CdS by simply adjusting the Se:S precursor ratio. This allows for tuning of the absorption and emission properties of the nanowires across the visible spectrum. The CdSeS nanowires have a wurtzite crystal structure and grow along the [001] direction. As measured by femtosecond transient absorption spectroscopy, the short component of the excited state lifetime remains relatively constant at ~10 ps with increasing Se; however the contribution of this short lifetime component increased dramatically from 8.4% to 57.7% with increasing Se content. These CdSeS nanowires offer facile synthesis and widely adjustable optical properties, characteristics which give them broad potential applications in the fields of optoelectronics, and photovoltaics.

View Webinar

Thursday, April 10, 2014Posted by Jeff Christians

Dr. James Radich

Congratulations to Dr. James Radic h on successful completion of his Ph. D. in Chemical and Biomolecular Engineering! James successfully defended his doctoral thesis entitled:

Reduced Graphene Oxide-Based Nanoassembiles for Energy Storage.

Congratulations on completion of your Ph. D. James!

Monday, April 7, 2014Posted by Jeff Christians

Dr. Sachidananda Krishnamurthy

Congratulations to Dr. Sachi Krishnamurthy on successful completion of his Ph. D. in Chemistry! Sachi successfully defended his doctoral thesis entitled:

Graphene-Based Assemblies: Electron Transfer Processes and Energy Conversion Applications.

Congratulations on completion of your Ph. D. Sachi!

Monday, April 7, 2014Posted by Jeff Christians

Editorial on Citation

Read this editorial, entitled "Cite with a Sight," from Prashant and Journal of Physical Chemistry Letters Editor-in-Chief George C. Schatz on the important area of citations in scientific research.

"Citing references in a scientific paper is becoming an increasingly important albeit challenging experience as the volume of scientific literature continues to explode. Despite the increasing average number of cited references in published papers, important and relevant papers are sometimes absent. Journal guidelines may recommend or even require the total number of citations be kept to a modest level. Consequently, authors need a balanced approach in identifying and including only the most relevant citations. In this Editorial, we discuss the importance of selecting and citing references correctly. We also discuss the impact of cited references on published research and their role in advancing the scientific discipline."

View Paper

Wednesday, March 26, 2014Posted by Jeff Christians

Hydrogen Evolution with Gold Clusters

Read the latest paper from the Kamat Lab!

Glutathione Capped Gold Nanoclusters as Photosensitizers. Visible Light Induced Hydrogen Generation in Neutral Water

Abstract: Glutathione capped metal nanoclusters (Aux-GSH NCs) which exhibit molecular like properties are employed as a photosen-sitizer for hydrogen generation in a photoelectrochemical cell (PEC) and a photocatalytic slurry reactor. The reversible re-duction (E0= -0.63 V vs. RHE) and oxidation (E0= 0.97 V and 1.51 V vs. RHE) potentials of these metal nanoclusters make them suita-ble for driving the water splitting reaction. When a mesoscopic TiO2 film sensitized by Aux-GSH NCs was used as the pho-toanode with a Pt counter electrode in aqueous buffer solution (pH = 7), we observe significant photocurrent activity under visible light (400 - 500 nm) excitation. Additionally, sensitizing Pt/TiO2 nanoparticles with Aux-GSH NCs in an aqueous slurry system and irradiating with visible light produced H2 at a rate of 0.3 mmole of hydrogen/hr/gram of Aux-GSH NCs. The rate of H2 evolution was significantly enhanced (~5 times) when a sacrificial donor, such as EDTA, was introduced into the sys-tem. Using metal nanoclusters as a photosensitizer for hydrogen generation lays the foundation for the future exploration of other metal nanoclusters with well controlled numbers of metal atoms and capping ligands.

View Paper

Wednesday, March 19, 2014Posted by Jeff Christians

Size Dependent Electron Transfer from CdSe to GO

Read the latest paper from the Kamat Lab!

CdSe-Graphene Oxide Light Harvesting Assembly. Size Dependent Electron Transfer and Light Energy Conversion Aspects

CdSe-Graphene Oxide Light Harvesting Assembly. Size Dependent Electron Transfer and Light Energy Conversion Aspects

Abstract: Excited state interaction between CdSe quantum dots (QD) of different sizes (2.3, 3.2 and 4.2 nm diameter) and graphene oxide (GO) has been probed by depositing them as films on conducting glass electrodes. The emission of smaller CdSe QDs (2.3 nm) is quenched by GO three times faster than that of larger QDs (4.2 nm). Electrophoretic deposition method has allowed us to sequentially deposit single or multiple layers of different sized QDs and GO assemblies on conducting glass electrode and achieve the modulation of photoresponse in photoelectrochemical solar cells. Superior photoconversion efficiency through the incorporation of GO is attributed to the improved charge separation in the composite assembly.

View Paper

Monday, March 17, 2014Posted by Jeff Christians

JACS & JPC Lett. Virtual Issue - Perovskites

Organometal Halide Perovskites for Transformative Photovoltaics

Prashant, with the help of The Journal of the American Chemical Society and The Journal of Physical Chemistry Letters, has put together a virtual issue on organometal perovskite photovoltaics. This issue highlights some of the important work in JACS and JPC Lett. on this exciting new field of photovoltaic research.

Read all of these great papers free of charge for a limited time! Including our recent paper where we use Copper Iodide as an inexpensive alternative hole conductor in perovskite solar cells.

An Inorganic Hole Conductor for Organo-Lead Halide Perovskite Solar Cells. Improved Hole Conductivity with Copper Iodide
Christians, J. A.; Fung, R. C. A.; Kamat, P. V. J. Am. Chem. Soc. 2014, 136 (2), 758-764.

Also, read Prashant's editorial on this exciting new research field,

Organometal Halide Perovskites for Transformative Photovoltaics
P.V. Kamat, J. Am. Chem. Soc. 2014, 136 (10), 3713–3714.

View Issue

Monday, March 17, 2014Posted by Jeff Christians

Feature Article - Hole Transfer in QDSCs

Read the latest paper from the Kamat Lab - a feature article in the journal Langmuir!

Quantum Dot Solar Cells. Hole Transfer as a Limiting Factor in Boosting Photoconversion Efficiency

Quantum Dot Solar Cells. Hole Transfer as a Limiting Factor in Boosting Photoconversion Efficiency

Abstract: Semiconductor nanostructures are attractive for designing low cost solar cells with tunable photoresponse. The recent advances in size and shape selective synthesis have enabled the design of quantum dot solar cells with photoconversion efficiencies greater than 5%. In order to make them competitive with other existing thin film or polycrystalline photovoltaic technologies, it is important to overcome kinetic barriers for charge transfer at semiconductor interfaces. This feature focuses on the limitations imposed by slow hole transfer in improving solar cell performance and its role in the stability of metal chalcogenide solar cells. Strategies to improve the rate of hole transfer through surface modified redox relays offer new opportunities to overcome the hole transfer limitation. The mechanistic and kinetic aspects of hole transfer in Quantum Dot Solar Cells (QDSCs), Nanowire Solar Cells (NWSCs) and Extremely Thin Absorber (ETA) solar cells are discussed.

View Paper

Wednesday, March 12, 2014Posted by Jeff Christians

ACS Applied Materials and Interfaces - Cover Article

ACS Applied Materials and Interfaces - Cover Article

Congratulations to Doug Hines on a great cover art in the journal ACS Applied Materials and Interfaces! The cover art appeared in this month's issue of ACS Appl. Mater. Interfaces to go along with Doug's review of Quantum Dot Surface Chemistry entitled, Recent Advances in Quantum Dot Surface Chemistry.

About the Image: Size-dependent electronic and optical properties of semiconductor nanocrystals or quantum dots (QDs) make them attractive for designing photovoltaic, electronic, and optoelectronic devices. Because of a high surface-to-volume ratio, the optical behavior of QDs becomes sensitive to surface-bound species. Chemical modification of QD surfaces is thus a convenient approach to influence the excited state dynamics and charge transfer properties. The illustration shows how ligand exchange between organic molecules can modify the QD surface and thus their excited state properties. With increasing exchange, one can visually see the change in the emission properties of QDs.

View Issue

Wednesday, March 12, 2014Posted by Jeff Christians

Simple Tuning of CdSeS NWs

Read the latest paper from the Kamat Lab!

CdSeS Nanowires. Compositionally Controlled Band Gap and Exciton Dynamics

CdSeS Nanowires. Compositionally Controlled Band Gap and Exciton Dynamics

Abstract: CdS, CdSe and ternary CdSexS(1-x) are some of the most widely studied II-VI semiconductors due to their wide range of applications and promising performance in numerous systems. One-dimensional semiconductor nanowires offer the ability to conduct charges efficiently along the length of the wire which has potential charge transport benefits compared to nanoparticles. Herein, we report a simple, inexpensive synthetic procedure for high quality CdSeS nanowires where the composition can be easily modulated from pure CdSe to pure CdS by simply adjusting the Se:S precursor ratio. This allows for tuning of the absorption and emission properties of the nanowires across the visible spectrum. The CdSeS nanowires have a wurtzite crystal structure and grow along the [001] direction. As measured by femtosecond transient absorption spectroscopy, the short component of the excited state lifetime remains relatively constant at ~10 ps with increasing Se; however the contribution of this short lifetime component increased dramatically from 8.4% to 57.7% with increasing Se content. These CdSeS nanowires offer facile synthesis and widely adjustable optical properties, characteristics which give them broad potential applications in the fields of optoelectronics, and photovoltaics.

View Paper

Thursday, March 6, 2014Posted by Jeff Christians

Publishing Scientific Research

Prashant and the other editors at the Journal of Physical Chemistry Letters have published a number of great editorials on scientific publishing. The topics range from scientific writing, to review, to multimedia.

The editorials offer helpful insight into the scientific publishing process and help authors increase the impact of their work.

Monday, February 24, 2014Posted by Jeff Christians

C&EN Cover Story - Perovskite Solar Cells

C&EN Cover Story - Perovskite Solar Cells

Chemical & Engineering News (C&EN) senior correspondant Mitch Jacoby recently visited our research group to talk about the exciting up and coming field of perovskite solar cells. Now, C&EN has run a great cover story article on this emerging research field. Dr. Kamat is quoted in the article and Joe Manser, a 3rd year Chemical and Biomolecular Engineering graduate student made the cover of the issue. You can read the full article on C&EN's website by following the link below.

"Every now and again, a well-studied research topic explodes with new life. Long after carbon materials filled chapters of dated textbooks, for example, that field's soul was reenergized around 1990 after buckyballs and carbon nanotubes were discovered. It happened again in that field about a half-dozen years ago when graphene took the world by storm. It's happening now in photovoltaics." - C&EN (image credit: Mitch Jacoby)

View Article

Monday, February 10, 2014Posted by Jeff Christians

Excited State of [9]- and [12]-CPP

Read the latest paper from the Kamat Lab!

Carbon Nanohoops: Excited Singlet and Triplet Behavior of [9]- and [12]-cycloparaphenylene

Carbon Nanohoops: Excited Singlet and Triplet Behavior of [9]- and [12]-cycloparaphenylene

Abstract: Cycloparaphenylene molecules, commonly known as 'carbon nanohoops,' have the potential to serve as building blocks in constructing carbon nanotube architectures. The singlet and triplet excited state characteristics of [9]-cycloparaphenylene ([9]CPP) and [12]-cycloparaphenylene ([12]CPP) have now been elucidated using time resolved transient absorption and emission techniques. The fluorescence quantum yields (Φ) of [9]CPP and [12]CPP were determined to be 0.46 and 0.83 respectively. Rates of non-radiative recombination (knr), radiative recombination (kr) and intersystem crossing (kisc) determined in this study indicate that radiative decay dominates in these nanohoop structures. The triplet quantum yields determined through energy transfer with excited biphenyl triplet were 0.18 and 0.13 for [9]CPP and [12]CPP respectively. The rate of triplet state quenching by oxygen was measured to be 1.7 × 103 s-1 ([9]CPP) and 1.9 × 103 s-1 ([12]CPP). The excited state dynamics established in this study enable us to understand the behavior of a carbon nanotube-like structure on a single subunit level.

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Monday, February 10, 2014Posted by Jeff Christians

Improved Charge Separation in CdSe QDSC with CuxS

Read the latest paper from the Kamat Lab!

Charge Transfer Mediation Through CuxS. The Hole Story of CdSe in Polysulfide

Charge Transfer Mediation Through CuxS. The Hole Story of CdSe in Polysulfide

Abstract: Hole transfer to dissolved sulfide species in liquid junction CdSe quantum dot sensitized solar cells is relatively slow when compared to electron transfer from CdSe to TiO2. Controlled exposure of cadmium chalcogenide surfaces to copper ions followed by immersion in sulfide solution promotes development of interfacial CuxS layer, which mediates hole transfer to polysulfide electrolyte by collection of photogenerated holes from CdSe. In addition, CuxS was also found to interact directly with defect states on the CdSe surface and quench emission characteristic of electron traps resulting from selenide vacancies. Together these effects were found to work in tandem to deliver 6.6% power conversion efficiency using Mn-doped CdS and CdSe co-sensitized quantum dot solar cell. Development of n-p interfacial junction at the photoanode-electrolyte interface in quantum dot solar cells unveils new means for designing high efficiency liquid junction solar cells.

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Monday, February 10, 2014Posted by Jeff Christians

Quantum Dot Surface Chemistry

Read the latest paper from the Kamat Lab!

Recent Advances in Quantum Dot Surface Chemistry

Recent Advances in Quantum Dot Surface Chemistry

Abstract: Quantum dot (QD) surface chemistry is an emerging field in semiconductor nanocrystal related research. Along with size manipulation, the careful control of QD surface chemistry allows modulation of the optical properties of a QD suspension. Even a single molecule bound to the surface can introduce new functionalities. Herein, we summarize the recent advances in QD surface chemistry and the resulting effects on optical and electronic properties. Specifically, the feature article focuses addresses three main issues: (i) How surface chemistry affects the optical properties of QDs, (ii) How it influences the excited state dynamics and (iii) How one can manipulate surface chemistry to control the interactions between QDs and metal oxides, metal nanoparticles and in self-assembled QD monolayers.

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Thursday, January 31, 2014Posted by Jeff Christians

Webinar - Rate Limiting Interfacial Hole Transfer in Sb2S3

Rate Limiting Hole Transfer in Sb2S3 Solar Cells

Watch this webinar on the hole transfer process between Sb2S3 and CuSCN. The hole diffusion coefficient and diffusion length in Sb2S3 is measured. Hole transfer from Sb2S3 to CuSCN is found to be predominately limited by transfer across the Sb2S3–CuSCN interface. It is based off of the paper, recently published in the Energy and Environmental Science, entitled:

Rate Limiting Interfacial Hole Transfer in Sb2S3 Solid-State Solar Cells.

Abstract: Transfer of photogenerated holes from the absorber species to the p-type hole conductor is fundamental to the performance of solid-state sensitized solar cells. In this study, we comprehensively investigate hole diffusion in the Sb2S3 absorber and hole transfer across the Sb2S3–CuSCN interface in the TiO2/Sb2S3/CuSCN system using femtosecond transient absorption spectroscopy, carrier diffusion modeling, and photovoltaic performance studies. Transfer of photogenerated holes from Sb2S3 to CuSCN is found to be dependent on Sb2S3 film thickness, a trend attributed to diffusion in the Sb2S3 absorber. However, modeling reveals that this process is not adequately described by diffusion limitations alone as has been assumed in similar systems. Therefore, both diffusion and transfer across the Sb2S3–CuSCN interface are taken into account to describe the hole transfer dynamics. Modeling of diffusion and interfacial hole transfer effects reveal that interfacial hole transfer, not diffusion, is the predominate factor dictating the magnitude of the hole transfer rate, especially in thin (< 20 nm) Sb2S3 films. Lastly, the implications of these results are further explored by photovoltaic measurements using planar TiO2/Sb2S3/CuSCN solar cells to elucidate the role of hole transfer in photovoltaic performance.

View Webinar

Wednesday, January 29, 2014Posted by Jeff Christians

Driving Charge Separation in Hybrid Materials

Read the latest paper from the Kamat Lab!

Driving Charge Separation for Hybrid Solar Cells: Photo-induced Hole Transfer in Conjugated Copolymer and Semiconductor Nanoparticle Assemblies

Driving Charge Separation for Hybrid Solar Cells: Photo-induced Hole Transfer in Conjugated Copolymer and Semiconductor Nanoparticle Assemblies

Abstract: This work reports on the use of an internal electrostatic field to facilitate charge separation at inorganic-organic interfaces, analogous to those in hybrid solar cells. Systematic charge transfer studies show that the donor-acceptor charge transfer rate is highly sensitive to the direction of the internal electric field.

View Paper

Monday, January 27, 2014Posted by Jeff Christians

Hole Transfer and Diffusion in Sb2S3

Read the latest paper from the Kamat Lab!

Rate Limiting Interfacial Hole Transfer in Sb2S3 Solid-State Solar Cells

Rate Limiting Interfacial Hole Transfer in Sb2S3 Solid-State Solar Cells

Abstract: Transfer of photogenerated holes from the absorber species to the p-type hole conductor is fundamental to the performance of solid-state sensitized solar cells. In this study, we comprehensively investigate hole diffusion in the Sb2S3 absorber and hole transfer across the Sb2S3–CuSCN interface in the TiO2/Sb2S3/CuSCN system using femtosecond transient absorption spectroscopy, carrier diffusion modeling, and photovoltaic performance studies. Transfer of photogenerated holes from Sb2S3 to CuSCN is found to be dependent on Sb2S3 film thickness, a trend attributed to diffusion in the Sb2S3 absorber. However, modeling reveals that this process is not adequately described by diffusion limitations alone as has been assumed in similar systems. Therefore, both diffusion and transfer across the Sb2S3–CuSCN interface are taken into account to describe the hole transfer dynamics. Modeling of diffusion and interfacial hole transfer effects reveal that interfacial hole transfer, not diffusion, is the predominate factor dictating the magnitude of the hole transfer rate, especially in thin (< 20 nm) Sb2S3 films. Lastly, the implications of these results are further explored by photovoltaic measurements using planar TiO2/Sb2S3/CuSCN solar cells to elucidate the role of hole transfer in photovoltaic performance.

View Paper

Thursday, January 9, 2014Posted by Jeff Christians

Aqueous OH Mediated Degradation of Dimethyl Phthalate

Read the latest paper from the Kamat Lab!

Kinetics and Mechanism of OH Mediated Degradation of Dimethyl Phthalate in Aqueous Solution: Experimental and Theoretical Studies

Excited State Behavior of Luminescent Glutathione Protected Gold Clusters

Abstract: The hydroxyl radical (•OH) is one of the main oxidative species in aqueous phase advanced oxidation processes, and its initial reactions with organic pollutants are important to understand the transformation and fate of organics in water environments. Insights into the kinetics and mechanism of •OH mediated degradation of the model environmental endocrine disruptor, dimethyl phthalate (DMP), have been obtained using radiolysis experiments and computational methods. The bimolecular rate constant for the •OH reaction with DMP was determined to be (3.2 ± 0.1) × 109 M–1s–1. The possible reaction mechanisms of radical adduct formation (RAF), hydrogen atom transfer (HAT), and single electron transfer (SET) were considered. By comparing the experimental absorption spectra with the computational results, it was concluded that the RAF and HAT were the dominant reaction pathways, and OH-adducts (•DMPOH1, •DMPOH2) and methyl type radicals •DMP(-H)α were identified as dominated intermediates. Computational results confirmed the identification of transient species with maximum absorption around 260 nm as •DMPOH1 and •DMP(-H)α, and these radical intermediates then converted to monohydroxylated dimethyl phthalates and monomethyl phthalates. Experimental and computational analyses which elucidated the mechanism of •OH-mediated degradation of DMP are discussed in detail.

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Tuesday, January 7, 2014Posted by Jeff Christians

Phys.org Highlights Perovskite Solar Cells

Perovskite solar cells become even more promising with cheaper materials

Lisa Zyga of the website Phys.org has written a great piece highlighting the copper iodide based perovskite solar cells recently developed in our lab. The entire article can be found at their website by following the link below.

Perovskite solar cells become even more promising with cheaper materials
"(Phys.org) — Due to their rapid improvements in a short amount of time, perovskite solar cells have become one of today's most promising up-and-coming photovoltaic technologies. Currently, the record efficiency for a perovskite solar cell is 15% and expected to improve further. Although the perovskite material itself is relatively inexpensive, the best devices commonly use an expensive organic hole-conducting polymer, called spiro-OMeTAD, which has a commercial price that is more than 10 times that of gold and platinum."

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Tuesday, December 31, 2013Posted by Jeff Christians

Updated Research Pages

Research Pages

Our research focuses on the fields of alternative energy and environmental research, with a special emphasis on an understanding of the fundamental science behing these processes which guides our development of improved devices for real world applications. We seek to build better devices by better understanding how they work.

View an updated summary of all of the ongoing research in the Kamat Lab on our research pages. We provide a brief description of our field and the specific challenges that we seek to address in our lab along with a description of recent developments from our research and select publications. Visit all of the different research pages to get a full overview of our current work!

Research Pages

Tuesday, December 24, 2013Posted by Jeff Christians

Webinar - Copper Iodide-Lead Iodide Perovskite Solar Cells

CuI Perovskite Solar Cells

Watch this webinar on an inorganic hole conductor for the emerging perovskite solar cells with efficiencies as high as 6% compared to 7.9% with sprio-OMeTAD. It is based off of the paper, recently published in the Journal of the American Chemical Society, entitled:

An Inorganic Hole Conductor for Organo-Lead Halide Perovskite Solar Cells. Improved Hole Conductivity with Copper Iodide.

Abstract: Organo-lead halide perovskite solar cells have emerged as one of the most promising candidates for the next generation of solar cells. To date, these perovskite thin film solar cells have exclusively employed organic hole conducting polymers which are often expensive and have low hole mobility. In a quest to explore new inorganic hole conducting materials for these perovskite based thin film photovoltaics, we have identified copper iodide as a possible alternative. Using copper iodide, we have succeeded in achieving a promising power conversion efficiency of 6.0% with excellent photocurrent stability. The open-circuit voltage, compared to the best spiro-OMeTAD devices, remains low and is attributed to higher recombination in CuI devices as determined by impedance spectroscopy. However, impedance spectroscopy revealed that CuI exhibits two orders of magnitude higher electrical conductivity than spiro-OMeTAD which allows for significantly higher fill factors. Reducing the recombination in these devices could render CuI as a cost effective competitor to spiro-OMeTAD in perovskite solar cells.

View Webinar

Thursday, December 19, 2013Posted by Jeff Christians

Kamat Group 2013 Annual Report

Kamat Group 2013 Annual Report

2013 has been a very productive year for the Kamat group. Our group said goodbye to Dr. Sean Murphy who successfully defended his thesis and received a postdoc at the University of Melbourne, as well as postdocs Ganganahalli Ramesha, and Pralay Santra. Three new graduate students joined the lab, Seogjoon Yoon, Victoria Bridewell, and Steven Kobosko, as well as two postdocs, Rabeka Alam, and Kevin Stamplecoskie. Prashant received numerous awards and recognitions, including the Langmuir Lectureship Award, gave invited presentations at 8 universities around the world, and gave 19 presentations at 13 different conferences! Definitely a lot of traveling this year! As a group, the research in the Kamat lab continues to be highly productive with Prashant's h-index surpassing 100 this year and 18 new publications. As a group, we would like to extend our thanks to all those who have contributed to making this research group successful! Best wishes for a happy and prosperous new year!

2013 Report

Thursday, December 19, 2013Posted by Jeff Christians

Excited State Dynamics of Au Clusters

Read the latest paper from the Kamat Lab!

Excited State Behavior of Luminescent Glutathione Protected Gold Clusters

Excited State Behavior of Luminescent Glutathione Protected Gold Clusters

Abstract: The excited state behavior of luminescent gold clusters provide new insights in understanding their photocatalytic activity in the visible region. The excited state of glutathione protected gold nanoclusters (AuGSH) which is characterized by the long-lived excited state (τ = 780 ns) arises from the ligand-to-metal type transition. These AuGSH clusters are in a partially oxidized state, (Au(I))and are readily reduced by chemical or electrochemical methods. Interestingly a metal core transition with short lived lifetime (τ <3 ps) appears along with a longer lifetime in reduced AuGSH clusters. The role of oxidation state of gold clusters in dictating the photocatalytic reduction of methyl viologen is discussed.

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Thursday, December 19, 2013Posted by Jeff Christians

Perovskite Solar Cells with Inorganic Hole Conductor

Read the latest paper from the Kamat Lab!

An Inorganic Hole Conductor for Organo-Lead Halide Perovskite Solar Cells. Improved Hole Conductivity with Copper Iodide

An Inorganic Hole Conductor for Organo-Lead Halide Perovskite Solar Cells. Improved Hole Conductivity with Copper Iodide

Abstract: Organo-lead halide perovskite solar cells have emerged as one of the most promising candidates for the next generation of solar cells. To date, these perovskite thin film solar cells have exclusively employed organic hole conducting polymers which are often expensive and have low hole mobility. In a quest to explore new inorganic hole conducting materials for these perovskite based thin film photovoltaics, we have identified copper iodide as a possible alternative. Using copper iodide, we have succeeded in achieving a promising power conversion efficiency of 6.0% with excellent photocurrent stability. The open-circuit voltage, compared to the best spiro-OMeTAD devices, remains low and is attributed to higher recombination in CuI devices as determined by impedance spectroscopy. However, impedance spectroscopy revealed that CuI exhibits two orders of magnitude higher electrical conductivity than spiro-OMeTAD which allows for significantly higher fill factors. Reducing the recombination in these devices could render CuI as a cost effective competitor to spiro-OMeTAD in perovskite solar cells.

View Paper

Thursday, December 19, 2013Posted by Jeff Christians

Direct Observation of GO Reduction Kinetics

Read the latest paper from the Kamat Lab!

Direct Observation of Spatially Heterogeneous Single-Layer Graphene Oxide Reduction Kinetics

Direct Observation of Spatially Heterogeneous Single-Layer Graphene Oxide Reduction Kinetics

Abstract: Graphene oxide (GO) is an important precursor in the production of chemically derived graphene. During reduction, GO's electrical conductivity and band gap change gradually. Doping and chemical functionalization are also possible, illustrating GO's immense potential in creating functional devices through control of its local hybridization. Here we show that laser-induced photolysis controllably reduces individual single-layer GO sheets. The reaction can be followed in real time through sizable decreases in GO's photoluminescence efficiency along with spectral blueshifts. As-produced reduced graphene oxide (rGO) sheets undergo additional photolysis, characterized by dramatic emission enhancements and spectral redshifts. Both GO's reduction and subsequent conversion to photobrightened rGO are captured through movies of their photoluminescence kinetics. Rate maps illustrate sizable spatial and temporal heterogeneities in sp2 domain growth and reveal how reduction "flows" across GO and rGO sheets. The observed heterogeneous reduction kinetics provides mechanistic insight into GO's conversion to chemically derived graphene and highlights opportunities for overcoming its dynamic, chemical disorder.

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Tuesday, December 17, 2013Posted by Jeff Christians

CdSe/CdS Nanowire Solar Cells

Read the latest paper from the Kamat Lab!

Sequentially Layered CdSe/CdS Nanowire Architecture for Improved Nanowire Solar Cell Performance

Sequentially Layered CdSe/CdS Nanowire Architecture for Improved Nanowire Solar Cell Performance

Abstract: The power conversion efficiency of semiconductor nanowire (NW) based solar cells as compared to quantum dot solar cell (QDSC) has remained lower, and efforts to improve the photovoltaic performance of semiconductor NWs continue. We have now succeeded in using a layered architecture of CdS and CdSe NWs for improving the photovoltaic performance of nanowire solar cell (NWSC). The photoanode designed with sequentially deposited films of CdSe and CdS NWs delivered a power conversion efficiency of 1%. This efficiency of CdSe/CdS composite is an order of magnitude improvement over single nanowire system (CdS or CdSe) based solar cell. The improvement seen in the CdSe/CdS composite film is attributed to charge rectification and improvement of electron and hole separation and transport in the opposite direction. Impedance spectroscopy demonstrates the beneficial effect of type II structure in CdSe/CdS sequential deposition through lower transport resistance, which remains a dominating effect in dictating the overall performance of the NWSC.

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Tuesday, December 17, 2013Posted by Jeff Christians

Eilers Fellowship Winner - Jeff Christians

Jeff Christians Eilers Graduate Student Fellowship Award Winner

Jeff Christians, a graduate student in our lab, was recently awarded the Patrick and Jana Eilers Graduate Student Fellowship for Energy Related Research on behalf of the center for sustainable energy at Notre Dame. This fellowship allows Jeff to further explore the emerging area of perovskite solar cells. Jeff will be working on understanding the hole transfer processes in these devices, and working to fabricate higher efficiency solar cells. Congratulations to Jeff for this award!

View Link

Monday, December 16, 2013Posted by Jeff Christians

Farewell Dr. Jong-Pil Kim

Dr. Jong-Pil Kim spent the past 9 months researching in the Kamat lab. Dr. Kim came to the University of Notre Dame as a visiting researcher from the Busan Center at the Korea Basic Science Institute in South Korea. During his time at Notre Dame, Dr. Kim studied the synthesis of CdSe, CdS and CdSeS nanowires for photovoltaic applications and greatly improved his English. As a group, we would like to thank Dr. Jong-Pil Kim for his time spent at Notre Dame and for his valuable contributions to our group!

Tuesday, November 19, 2013Posted by Jeff Christians

Testing Fruit-Sensitized Solar Cells

About 20 sophomore students at Notre Dame test dye-sensitized solar cells they made in lab using blueberry, raspberry, blackberry, or tea as the light absorber. Joe Manser, a third year chemical engineering graduate student in our lab, gave the students an introduction on how DSSCs work and then took them up into our lab and helped them measure the solar cells they made. This lab was developed in conjuction with Ken Poling, a science teacher at Penn High School in South Bend, through the Research Experience for Teachers (RET) program this past summer. Joe Manser and Jeff Christians worked with Ken to develop the techniques needed to make fruit-sensitized solar cells in the summer, and then helped the students as they measured their solar cell efficiency. It was a really great experience to help teach students about solar energy!

View Pictures

Tuesday, November 12, 2013Posted by Jeff Christians

CdS Nanowire Solar Cells and Squaraine

Read the latest paper from the Kamat Lab!

CdS Nanowire Solar Cells: Dual Role of Squaraine Dye as a Sensitizer and a Hole Transporter

CdS Nanowire Solar Cells: Dual Role of Squaraine Dye as a Sensitizer and a Hole Transporter

Abstract: The squaraine dye (SQ) anchored onto CdS nanowires serves as a photosensitizing dye and a hole acceptor. This dual role of the squaraine dye has been successfully exploited in a nanowire solar cell to improve the photoconversion efficiency. Electrophoretic deposition of CdS NWs and CdS NWs+SQ composite onto conducting glass electrodes was performed to obtain robust photoanodes and evaluate the photovoltaic performance of nanowire solar cells (NWSCs). Whereas the sensitization property of the SQ extends the response of CdS NWSCs into the near-IR (NIR) region, its redox property facilitates shuttling of holes to the electrolyte and suppressing the charge recombination process. Transient absorption measurements confirm the formation of cation radical of the dye arising from these two processes. The dual role of the squaraine dye has enabled us to improve the power conversion efficiency of NWSCs by a factor of ~20. Photoelectrochemical, spectroelectrochemical, and spectroscopic measurements provide insight into the multifaceted role of squaraine dye in improving the performance of NWSCs.

View Paper

Tuesday, October 21, 2013Posted by Jeff Christians

Kamat Lab Twitter: @KamatLabND

Kamat Lab Twitter

We now have a Kamat Lab twitter page! Follow the Kamat Lab on Twitter @KamatLabND. Find interesting research articles about different areas of science our lab is interested in and other papers that grabbed our attention. In addition, keep up to date with our latest publications and group news. Feel free to tweet us if you come across anything interesting, we'd love to hear from you!

You can find our Twitter page in the future by reminding to follow us or by simply clicking the blue Twitter bird on the right side of the navigation bar at the top of each page.

KamatLab Twitter

Monday, October 14, 2013Posted by Jeff Christians

Prashant Kamat - 30 years at ND

Prashant Kamat 30 years at Rad Lab

This year, Prashant is celebrating 30 years at the University of Notre Dame in the Radiation Laboratory. To help him celebrate, we planned a surprise cookout lunch for the entire Radiation Laboratory staff. Doug and Jeff grilled hamburgers and bratwursts (after taking an online food safety course), and James set up a fake conference call meeting with Prashant then lured him outside with a "safety hazard" that he wanted checked out. We had beautiful weather outside and great food!

Photo Album

Thursday, October 10, 2013Posted by Jeff Christians

Nickel-Doped MnO2 for Lithium Batteries

Read the latest paper from the Kamat Lab!

Nickel-Doped MnO2 Nanowires Anchored onto Reduced Graphene Oxide for Rapid Cycling Cathode in Lithium Ion Batteries

Nickel-Doped MnO2 for Lithium Batteries

Abstract: Nickel-doped MnO2 nanowires were synthesized directly onto reduced graphene oxide (RGO) to generate a composite cathode material with improved high-rate cycling characteristics. The presence of RGO improves the electrochemical characteristics of the cathode in Li-ion half-cell architecture. Cyclic voltammetry, electrochemical impedance spectroscopy, and electrode cycling are confirm that RGO plays a major role in enhancing the ability of the NixMn(1-x)O2 to reversibly intercalate lithium ions at 1C rate. The chronocoulometric response of the RGO-based electrode shows the improvements originate from faster reaction kinetics and transport of Li+ coupled with increased specific capacitance and Li+ adsorption.

View Paper

Friday, September 13, 2013Posted by Jeff Christians

Prashant Awarded 2013 Langmuir Lectureship

2013 Langmuir Lecture

Congratulations to Prashant on receiving the 2013 Langmuir Lectureship! Prashant gave his lecture entitled, "Meeting the Clean Energy Challenge with Semiconductor Nanostructures" at the 2013 ACS National Meeting in Indianapolis, Indiana. Prashant's lecture was so well attended that chairs had to be brought in from the neighboring lecture hall and there was still a large group standing in the back (and even out the back!) of the lecture hall. Prashant was one of two recipients of the award, along with Dr. Nicholas A. Kotov from the University of Michigan, which was co-sponsored by the ACS Division of Colloid & Surface Chemistry and the journal Langmuir. Join with us in the Kamat group in congratulating Prashant on this wonderful career achievement!

Langmuir Lecture

Tuesday, August 20, 2013Posted by Jeff Christians

Webinar - Sb2S3 Hole Transfer

Galvanic Exchange on RGO

Watch this webinar on the transfer of holes from Sb2S3 to CuSCN. This webinar describes the experimental results and the observed mechanism of the hole transfer. It is based off of the paper, recently published in ACS Nano, entitled:

Trap and Transfer. Two-Step Hole Injection Across the Sb2S3/CuSCN Interface in Solid State Solar Cells.

Abstract: In solid-state semiconductor-sensitized solar cells, commonly known as extremely thin absorber (ETA) or solid-state quantum dot sensitized solar cells (QDSCs), transfer of photogenerated holes from the absorber species to the p-type hole conductor plays a critical role in the charge separation process. Using Sb2S3 (absorber) and CuSCN (hole conductor), we have constructed ETA solar cells exhibiting a power conversion efficiency of 3.3%. The hole transfer from excited Sb2S3 into CuSCN, which limits the overall power conversion efficiency of these solar cells, is now independently studied using transient absorption spectroscopy. In the Sb2S3 absorber layer, photogenerated holes are rapidly localized on the sulfur atoms of the crystal lattice, forming a sulfide radical (S−•) species. This trapped hole is transferred from the Sb2S3 absorber to the CuSCN hole conductor with an exponential time constant of 1680 ps. This process was monitored through the spectroscopic signal seen for the S−• species in Sb2S3, providing direct evidence for the hole transfer dynamics in ETA solar cells. Elucidation of the hole transfer mechanism from Sb2S3 to CuSCN represents a significant step toward understanding charge separation in Sb2S3 solar cells, and provides insight into the design of new architectures for higher efficiency devices.

View Webinar

Thursday, August 15, 2013Posted by Jeff Christians

Sb2S3 Hole Transfer

Read the latest paper from the Kamat Lab!

Trap and Transfer. Two-Step Hole Injection Across the Sb2S3/CuSCN Interface in Solid State Solar Cells.

Sb2S3/CuSCN Hole Transfer

Abstract: In solid-state semiconductor-sensitized solar cells, commonly known as extremely thin absorber (ETA) or solid-state quantum dot sensitized solar cells (QDSCs), transfer of photogenerated holes from the absorber species to the p-type hole conductor plays a critical role in the charge separation process. Using Sb2S3 (absorber) and CuSCN (hole conductor), we have constructed ETA solar cells exhibiting a power conversion efficiency of 3.3%. The hole transfer from excited Sb2S3 into CuSCN, which limits the overall power conversion efficiency of these solar cells, is now independently studied using transient absorption spectroscopy. In the Sb2S3 absorber layer, photogenerated holes are rapidly localized on the sulfur atoms of the crystal lattice, forming a sulfide radical (S−•) species. This trapped hole is transferred from the Sb2S3 absorber to the CuSCN hole conductor with an exponential time constant of 1680 ps. This process was monitored through the spectroscopic signal seen for the S−• species in Sb2S3, providing direct evidence for the hole transfer dynamics in ETA solar cells. Elucidation of the hole transfer mechanism from Sb2S3 to CuSCN represents a significant step toward understanding charge separation in Sb2S3 solar cells, and provides insight into the design of new architectures for higher efficiency devices.

View Webinar

Thrusday, June 20, 2013Posted by Jeff Christians

Quantum Dot Surface Chemistry

Read the latest paper from the Kamat Lab!

Quantum Dot Surface Chemistry: Ligand Effects and Electron Transfer Reactions.

Quantum Dot Surface Chemistry

Abstract: With the increased interest in quantum dot sensitized solar cells (QDSCs) there comes a need to better understand how surface modification of quantum dots (QDs) can affect the excited state dynamics of QDs, electron transfer at the QD-metal oxide (MO) interface, and overall photoconversion efficiency of QDSCs. We have monitored the surface modification of solution based QDs via the steady-state absorption and emission characteristics of colloidal CdSe passivated with β-Alanine (β-Ala). The trap-remediating nature of the β-Ala molecule, arising from the Lewis-basicity of the amine group, is realized from the hypsochromic shifts seen in excitonic absorption and emission bands as well as an increase in fluorescence quantum yield. Transient absorption measurements of CdSe-TiO2 films prepared with and without β-Ala as a linker molecule further reveal the role of the surface modifier in influencing excited state electron transfer processes. Electron transfer at this interface was dependent on the method of QD deposition: CdSe-TiO2 (direct deposition, ket = 1.5 × 10^10 s-1), CdSe-linker-TiO2 (attaching linker molecule first to TiO2 so that β-Ala interaction is minimal, ket = 2.4 × 10^9 s-1) or linker-CdSe-linker-TiO2 (linkage via full β-Ala encapsulation in solution prior to deposition, ket = 6.4 × 10^8 s-1). These results imply that the surface chemistry of colloidal CdSe plays an important role in mediating electron transfer reactions.

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Thrusday, June 6, 2013Posted by Jeff Christians

Metal-Cluster-Sensitized Solar Cells

Read the latest paper from the Kamat Lab!

Metal-Cluster-Sensitized Solar Cells. A New Class of Thiolated Gold Sensitizers Delivering Efficiency Greater Than 2%.

Holey Graphene Oxide

Abstract: A new class of metal-cluster sensitizers has been explored for designing high-efficiency solar cells. Thiol-protected gold clusters which exhibit molecular-like properties have been found to inject electrons into TiO2 nanostructures under visible excitation. Mesoscopic TiO2 films modified with gold clusters deliver stable photocurrent of 3.96 mA/cm2 with power conversion efficiencies of 2.3% under AM 1.5 illumination. The overall absorption features and cell performance of metal-cluster-sensitized solar cells (MCSCs) are comparable to those of CdS quantum-dot-based solar cells (QDSCs). The relatively high open-circuit voltage of 832 mV and fill factor of 0.7 for MCSCs as compared to QDSCs show the viability of these new sensitizers as alternatives to semiconductor QDs and sensitizing dyes in the next generation of solar cells. The superior performance of MCSCs discussed in this maiden study lays the foundation to explore other metal clusters with broader visible absorption.

View Paper

Thrusday, June 6, 2013Posted by Jeff Christians

Perspective Article - Energy Outlook for Planet Earth

Read the latest paper from the Kamat Lab!

Energy Outlook for Planet Earth

Holey Graphene Oxide

Growing economies and increasing population will necessitate an increased energy supply in the coming years. A recent BP report of the 2030 Energy Outlook suggests that an additional 1.3 billion people will become new energy consumers by 2030. If the current energy growth of 1.6% per year continues, this would require the energy production to double in about 40 years. In fact, Exxon's 2040 Energy Outlook projects an 85% increase in global electricity demand over the period of 2010–2040. Developing (nonOECD) countries alone will experience a 150% surge in electricity demand. The sheer magnitude of this energy demand will require us to make some tough choices: either continue to build the same number of coal and nuclear power plants or explore the production of renewable energy coupled with improved efficiency of energy usage (Figure).

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Monday, May 20, 2013Posted by Jeff Christians

Alex Mobashery 4th in International Science Fair

Alex Mobashery Intel International Science and Engineering Fair

Alex Mobashery, a Penn High School, Mishawaka student carried out research in the Kamat laboratory for the past two years (his junior and senior year). Recently, he participated in the Intel International Science and Engineering Fair 2013.

His Project "Boosting Current of Quantum Dot Sensitized Solar Cells with CdS/PbS Heterostructures" placed fourth in the Energy and Transportation category of the Grand Award Winner.

Join us in congratulating Alex on his great work in our lab and awesome showing at the Science and Engineering Fair!

List of Winners

Monday, May 20, 2013Posted by Jeff Christians

Fellowship Winner - James Radich

James Radich Fellowships

James Radich, a graduate student in our lab, was recently awarded two fellowships that allow him to explore his own proposed research topics: the Eiler's Sustainable Energy Research Fellowship and the Bayer Environmental Research Fellowship. The energy research will focus on the incorporation of copper-based p-type nanocrystals into solid state quantum dot solar cells. The environmental research pivots from a recent publication on Holey Graphene and aims to understand the fate of graphene and other carbon nanomaterials in oxidative environments. Congratulations to James for these awards!

Tuesday, May 14, 2013Posted by Jeff Christians

Webinar - Making Graphene Holey

Galvanic Exchange on RGO

Watch this webinar the formation of holes in graphene due to gold-nanoparticle-mediated attack of the reduced graphene oxide sheet by hydroxyl radicals. This webinar is based off of the paper, recently published in ACS Nano, entitled:

Making Graphene Holey. Gold-Nanoparticle-Mediated Hydroxyl Radical Attack on Reduced Graphene Oxide

Abstract: Graphene oxide (GO) and reduced graphene oxide (RGO) have important applications in the development of new electrode and photocatalyst architectures. Gold nanoparticles (AuNPs) have now been employed as catalyst to generate OH and oxidize RGO via hydroxyl radical attack. The oxidation of RGO is marked by pores and wrinkles within the 2-D network. Nanosecond laser flash photolysis was used in conjunction with competition kinetics to elucidate the oxidative mechanism and calculate rate constants for the AuNP-catalyzed and direct reaction between RGO and OH. The results highlight the use of the AuNP-mediated oxidation reaction to tune the properties of RGO through the degree of oxidation and/or functional group selectivity in addition to the nanoporous and wrinkle facets. The ability of AuNPs to catalyze the photolytic decomposition of H2O2 as well as the hydroxyl radical-induced oxidation of RGO raises new issues concerning graphene stability in energy conversion and storage (photocatalysis, fuel cells, Li-ion batteries, etc.). Understanding RGO oxidation by free radicals will aid in maintaining the long-term stability of RGO-based functional composites where intimate contact with radical species is inevitable.

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Monday, May 13, 2013Posted by Jeff Christians

Webinar - Galvanic Exchange on Reduced Graphene Oxide

Galvanic Exchange on RGO

Watch this webinar on how to promote galvinic exchange on the surface of reduced graphene oxide for the design of new catalyst materials. This webinar is based off of the paper, published in the Journal of Physical Chemistry C, entitled:

Galvanic Exchange on Reduced Graphene Oxide. Designing a Multifunctional Two-Dimensional Catalyst Assembly.

Abstract: The two-dimensional network of reduced graphene oxide (RGO) is decorated with silver and gold nanoparticles. The silver nanoparticles deposited on RGO by photocatalytic reduction are subjected to galvanic exchange with Au3+ ions to transform them into gold nanoparticles. This compositional change on the RGO surface demonstrates RGO's versatile ability to anchor a wide array of nano-particles and facilitate chemical transformations. Coupled with RGO's unique ability to capture and transport electrons, galvanic exchange is used to contrive a two-dimensional nano catalyst mat. Raman studies show that metal nanoparticles anchored on reduced graphene oxide facilitate enhancement of Raman bands. Using methyl viologen as a probe we elucidate the photocatalytic activity of the Semiconductor-RGO-Metal nanoassembly and highlight the mediation of RGO in charge transfer processes.

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Friday, May 10, 2013Posted by Jeff Christians

Making Graphene Holy Holey

Read the latest paper from the Kamat Lab!

Making Graphene Holey. Gold-Nanoparticle-Mediated Hydroxyl Radical Attack on Reduced Graphene Oxide

Holey Graphene Oxide

Abstract: Graphene oxide (GO) and reduced graphene oxide (RGO) have important applications in the development of new electrode and photocatalyst architectures. Gold nanoparticles (AuNPs) have now been employed as catalyst to generate OH and oxidize RGO via hydroxyl radical attack. The oxidation of RGO is marked by pores and wrinkles within the 2-D network. Nanosecond laser flash photolysis was used in conjunction with competition kinetics to elucidate the oxidative mechanism and calculate rate constants for the AuNP-catalyzed and direct reaction between RGO and OH. The results highlight the use of the AuNP-mediated oxidation reaction to tune the properties of RGO through the degree of oxidation and/or functional group selectivity in addition to the nanoporous and wrinkle facets. The ability of AuNPs to catalyze the photolytic decomposition of H2O2 as well as the hydroxyl radical-induced oxidation of RGO raises new issues concerning graphene stability in energy conversion and storage (photocatalysis, fuel cells, Li-ion batteries, etc.). Understanding RGO oxidation by free radicals will aid in maintaining the long-term stability of RGO-based functional composites where intimate contact with radical species is inevitable.

View Paper