"Welcome to The Prashant Kamat lab at the University of Notre Dame! With the help of internal and external collaborations we have established a successful multidisciplinary research program in nanostructure architectures and energy conversion processes." - Prashant Kamat


Kamat Lab News


November 7, 2019Posted by Jeff DuBose

Probing Perovskite Photocatalysis. Interfacial Electron Transfer between CsPbBr3 and Ferrocene Redox Couple

Click here to go to the paper.


Probing Perovskite Photocatalysis. Interfacial Electron Transfer between CsPbBr<sub>3</sub> and Ferrocene Redox Couple

Abstract:
Interfacial charge transfer between a semiconductor nanocrystal and a molecular relay is an important step in nanomaterial photocatalysis. The ferrocene redox couple (Fc+/Fc0, E0 = −4.9 eV vs vacuum) has now been used as a model redox relay system to investigate photocatalytic properties of CsPbBr3 perovskite nanocrystals. The photocatalytic reduction of ferrocenium (Fc+) to ferrocene (Fc0) with CsPbBr3 nanocrystals was dictated by the surface interactions. Whereas a rapid quenching and subsequent recovery of CsPbBr3 emission is seen at low Fc+ concentrations, the quenched emission was sustained at higher Fc+ concentrations. The photoinduced interfacial electron transfer between CsPbBr3 and ferrocenium (Fc+) studied using transient absorption spectroscopy occurred with a rate constant of 1.64 × 1010 s–1. Better understanding of interfacial processes using redox probes can lead to the improvement in photocatalytic performance of perovskite nanocrystals.


Friday, August 30, 2019Posted by Jeff DuBose

Undergraduate Researcher Jake Drysdale Gives Poster Presentation about his project: "Halide Composition and Temperature Dependent Properties of Perovskite Solar Cells"

Click here to see the video!

Undergraduate researcher James Drysdale gives a video presentation for his poster entitled "Halide Composition and Temperature Dependent Properties of Perovskite Solar Cells" for the Notre Dame Summer Undergraduate Research Symposium.






Tuesday, July 23, 2019Posted by Jeff DuBose

Visiting researcher Tor Elmelund publishes his first paper while at the Kamat Lab!

Bidirectional Halide Ion Exchange in Paired Lead Halide Perovskite Films with Thermal Activation

Click here to go to the paper.


Bidirectional Halide Ion Exchange in Paired Lead Halide Perovskite Films with Thermal Activation

Abstract:
MAPbBr3 and MAPbI3 films cast onto glass slides and physically paired together undergo halide exchange to form mixed halide films. The change in halide composition in these two ∼130 nm thick films occurs concurrently with Br diffusing toward the MAPbI3 film and I diffusing toward the MAPbBr3 film. The diffusion of these halide species, which is tracked through changes in the absorption, offers a direct measurement of thermally activated halide diffusion in perovskite films. The increase in the rate constant of halide diffusion with increasing temperature (from 8.3 × 10–6 s–1 at 23 °C to 3.7 × 10–4 s–1 at 140 °C) follows an Arrhenius relationship with activation energy of 51 kJ/mol. The thermally activated halide exchange shows the challenges of employing layers of different metal halide perovskites in stable tandem solar cells.




Thursday, July 18, 2019Posted by Jeff DuBose

Come see what ND Energy has to say about associated researcher and Kamat Lab member Rebecca Scheidt


Rebecca Scheidt is entering her fourth year as a graduate student advised by Prof. Prashant Kamat in the Department of Chemistry and Biochemistry. She presented "Interfacial Charge Transfer between Excited CsPbBr3 Nanocrystals and TiO2: Charge Injection versus Photodegradation,” at the ND Energy PD&GS Luncheon in May. In 2018, Scheidt received the Patrick and Jana Eilers Graduate Student Fellowship for Energy Related Research for her project looking at cesium lead bromide perovskite nanocrystals and how they operate in a photovoltaic device stack. Because these next-generation materials absorb light so well, these nanocrystal solar cells can be placed into thin film and flexible technologies. “What I specifically look at is how they interacted with different charge transfer materials in the solar cell and whether that caused degradation under certain conditions,” Scheidt said. “In terms of making them more stable long-term, and looking at how they break down or degrade, we aim to make them more efficient overall.”

Click here to read the rest of the blurb from ND Energy


Monday, May 6, 2019Posted by Jeff DuBose

Dr. Kamat is recognized as one of the Clarivate Analytics' 2018 Highly Cited Researchers list! Congratulations, Dr. Kamat!


This list recognizes world-class researchers selected for their exceptional research performance, demonstrated by production of multiple highly cited papers that rank in the top 1% by citations for field and year in Web of Science. Click here for ND Energy's post about the Notre Dame Faculty who were awarded this prestigious honor.


Monday, March 18, 2019Posted by Jeff DuBose

Rebecca publishes the first paper in the new journal ACS Materials Letters!

(DOI: 10.1021/acsmaterialslett.9b00001)

Tracking Transformative Transitions: From CsPbBr3 Nanocrystals to Bulk Perovskite Films

Click here to go to the paper.


Tracking Transformative Transitions: From CsPbBr<sub>3</sub> Nanocrystals to Bulk Perovskite Films

Abstract:
The control of grain size and surface properties is an important parameter in controlling the optoelectronic and photovoltaic properties of metal halide perovskites. When CsPbBr3 nanocrystal (10 nm in diameter) films were annealed at 100–125 °C, they grow in size to produce 400 nm diameter crystallites while transforming into bulk perovskite films. Characteristic changes in the optical properties were noted when such transformation occurred from nanocrystals into bulk. By tracking absorbance and emission spectra and morphological changes of CsPbBr3 films at different annealing times and temperature, we were able to establish the mechanism of particle growth. The presence of nanocrystals and larger crystals during the intermediate annealing steps and narrowing size distribution confirmed the Ostwald ripening mechanism for the crystal growth. The energy of activation of crystal growth as determined from the temperature dependent optical properties was estimated to be 75 kcal/mol.


Friday, March 15, 2019Posted by Jeff DuBose

Tuning the Excited-State Dynamics of CuI Films with Electrochemical Bias

Click here to go to the paper.


Tuning the Excited-State Dynamics of CuI Films with Electrochemical Bias

Abstract:
Owing to its high hole conductivity and ease of preparation, CuI was among the first inorganic hole-transporting materials that were introduced early on in metal halide perovskite solar cells, but its full potential as a semiconductor material is still to be realized. We have now performed ultrafast spectroelectrochemical experiments on ITO/CuI electrodes to show the effect of applied bias on the excited-state dynamics in CuI. Under operating conditions, the recombination of excitons is dependent on the applied bias, and it can be accelerated by decreasing the potential from +0.6 to −0.1 V vs Ag/AgCl. Prebiasing experiments show the persistent and reversible “memory” effect of electrochemical bias on charge carrier lifetimes. The excitation of CuI in a CuI/CsPbBr3 film provides synergy between both CuI and CsPbBr in dictating the charge separation and recombination.


Thursday, November 15, 2018Posted by Jeff DuBose

Come listen to Dr. Kamat and Rebecca Scheidt present our latest research at MRS Boston 2018!

Click here for MRS 2018 full Program / Exhibit guide.


MRS Boston graphic

Dr. Kamat will be speaking on Monday, November 26th at 10:15am (ET) in Hynes Convention Center, Level 3 Ballroom C. The talk is entitled "Charge Injection from Excited CsPbBr3 Nanocrystals into TiO2 in Perovskite and Its Role in the Degradation of Perovskite Layer in Visible Light". Come listen to the latest research from the Kamat Lab!

Rebecca Scheidt, third year graduate student in the lab, will be speaking on Thursday, November 29th at 9am (ET) in Hynes Convention Center, Level 3 Room Ballroom B. The talk is entitled "Suppression of Halide Ion Exchange in Cesium Lead Halide Perovskites with PbSO4-Oleate Capping". Come learn what exciting things the Kamat Lab is up to!


Wednesday, October 24, 2018Posted by Jeff DuBose

Interfacial Charge Transfer between Excited CsPbBr3 Nanocrystals and TiO2: Charge Injection versus Photodegradation

Click here to listen to Rebecca Scheidt - third year grad student and first author of this paper - talk about her project via a LiveSlides presentation!


Interfacial Charge Transfer between Excited CsPbBr<sub>3</sub> Nanocrystals and TiO<sub>2</sub>: Charge Injection versus Photodegradation

Abstract:
Record-breaking efficiency achieved with quantum dot solar cells made of perovskite nanocrystals demands understanding of the excited-state interactions between perovskite nanocrystals and metal oxide electron transport layers. The interfacial electron transfer between excited CsPbBr3 perovskite nanocrystals and metal oxides (TiO2, SnO2, and ZnO) was elucidated using transient absorption spectroscopy and found to occur with a rate constant in the range of 2–4 × 1010 s–1. In an inert atmosphere, back electron transfer helps to maintain the stability of the perovskite nanocrystals. However, the presence of oxygen introduces instability as it scavenges away transferred electrons from the electron-transporting metal oxide, leaving behind holes to accumulate at CsPbBr3 nanocrystals, which in turn induce anodic corrosion. X-ray photoelectron spectroscopy measurements have enabled us to identify PbO as the major photodegraded product. The importance of the surrounding atmosphere and the supporting metal oxide in governing the stability of perovskite nanocrystals is discussed.


Tuesday, July 5, 2016Posted by Christian Talavera

Transformation of Sintered CsPbBr3 Nanocrystals to Cubic CsPbI3 and Gradient CsPbBrxI3-x through Halide Exchange

Read the latest paper from the Kamat Lab!

Transformation of Sintered CsPbI3 Nanocrystals to Cubic CsPbI3 and Gradient CsPbBrxI3-x through Halide Exchange

Transformation of Sintered CsPbBr<sub>3</sub> Nanocrystals to Cubic CsPbI<sub>3</sub> and Gradient CsPbBr<sub>x</sub>I<sub>3-x</sub> through Halide Exchange

Abstract: All-inorganic cesium lead halide (CsPbX3, X = Br-, I-) perovskites could potentially provide comparable photovoltaic performance with enhanced stability compared to organic-inorganic lead halide species. However, small-bandgap cubic CsPbI3 has been difficult to study due to challenges forming CsPbI3 in the cubic phase. Here, a low-temperature procedure to form cubic CsPbI3 has been developed through a halide exchange reaction using films of sintered CsPbBr3 nanocrystals. The reaction was found to be strongly dependent upon temperature, featuring an Arrhenius relationship. Additionally, film thickness played a significant role in determining internal film structure at intermediate reaction times. Thin films (50 nm) showed only a small distribution of CsPbBrxI3-x species, while thicker films (350 nm) exhibited much broader distributions. Furthermore, internal film structure was ordered, featuring a compositional gradient within film. Transient absorption spectroscopy showed the influence of halide exchange on the excited state of the material. In thicker films, charge carriers were rapidly transferred to iodide-rich regions near the film surface within the first several picoseconds after excitation. This ultrafast vectorial charge-transfer process illustrates the potential of utilizing compositional gradients to direct charge flow in perovskite-based photovoltaics.


Thursday, June 23, 2016Posted by Christian Talavera

Tracking Iodide and Bromide Ion Segregation in Mixed Halide Lead Perovskites during Photoirradiation

Read the latest paper from the Kamat Lab!

Tracking Iodide and Bromide Ion Segregation in Mixed Halide Lead Perovskites during Photoirradiation

 Tracking Iodide and Bromide Ion Segregation in Mixed Halide Lead Perovskites during Photoirradiation

Abstract: Mixed halide lead perovskites (e.g., CH3NH3PbBrxI3-x) undergo phase segregation creating iodide-rich and bromide-rich domains when subjected to visible irradiation. This intriguing aspect of halide ion movement in mixed halide films is now being tracked through excited-state behavior using emission and transient absorption spectroscopy tools. These transient experiments have allowed us to establish the time scale with which such separation occurs under laser irradiation (405 nm, 25 mW/cm2 to 1.7 W/cm2) as well as dark recovery. While the phase separation occurs with a rate constant of 0.1-0.3 s-1, the recovery occurs over a time period of several minutes to an hour. The relative photoluminescence quantum yield observed for Br-rich regions (em. max 530 nm) is nearly 2 orders of magnitude lower than that of I-rich regions (em. max 760 nm) and arises from the fact that I-rich regions serve as sinks for photogenerated charge carriers. Understanding such cascading charge transfer to localized sites could further enable the design of gradient halide structures in mixed halide systems.


Wednesday, June 22, 2016Posted by Christian Talavera

Intriguing Optoelectronic Properties of Metal Halide Perovskites

Read the latest paper from the Kamat Lab!

Intriguing Optoelectronic Properties of Metal Halide Perovskites

Intriguing Optoelectronic Properties of Metal Halide Perovskites

Abstract: A new chapter in the long and distinguished history of perovskites is being written with the breakthrough success of metal halide perovskites (MHPs) as solution-processed photovoltaic (PV) absorbers. The current surge in MHP research has largely arisen out of their rapid progress in PV devices; however, these materials are potentially suitable for a diverse array of optoelectronic applications. Like oxide perovskites, MHPs have ABX3 stoichiometry, where A and B are cations and X is a halide anion. Here, the underlying physical and photophysical properties of inorganic (A = inorganic) and hybrid organic-inorganic (A = organic) MHPs are reviewed with an eye toward their potential application in emerging optoelectronic technologies. Significant attention is given to the prototypical compound methylammonium lead iodide (CH3NH3PbI3) due to the preponderance of experimental and theoretical studies surrounding this material. We also discuss other salient MHP systems, including 2-dimensional compounds, where relevant. More specifically, this review is a critical account of the interrelation between MHP electronic structure, absorption, emission, carrier dynamics and transport, and other relevant photophysical processes that have propelled these materials to the forefront of modern optoelectronics research.




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