Showing papers by "Prashant V. Kamat published in 2019"
TL;DR: Transient absorption spectroscopy revealed that the iodide expulsion process leaves a defect-rich perovskite lattice behind as charge carrier recombination in the re-formed lattice is greatly accelerated.
Abstract: Halide ion mobility in metal halide perovskites remains an intriguing phenomenon, influencing their optical and photovoltaic properties. Selective injection of holes through electrochemical anodic ...
87 citations
TL;DR: The MAPbBr3 and MAPbI3 films cast onto glass slides and physically paired together undergo halide exchange to form mixed halide films as discussed by the authors, and the change in halide composition in these two ∼130 nm thick films...
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 ...
67 citations
51 citations
TL;DR: This work diagnosed the problems of conventional thiolated Ag NCs used for solar cell applications and developed a new synthesis route to form aggregation-induced emission (AIE)-type AgNCs that can significantly overcome these limitations.
Abstract: Intrinsic low stability and short excited lifetimes associated with Ag nanoclusters (NCs) are major hurdles that have prevented the full utilization of the many advantages of Ag NCs over their longtime contender, Au NCs, in light energy conversion systems. In this report, we diagnosed the problems of conventional thiolated Ag NCs used for solar cell applications and developed a new synthesis route to form aggregation-induced emission (AIE)-type Ag NCs that can significantly overcome these limitations. A series of Ag(0)/Ag(I)-thiolate core/shell-structured NCs with different core sizes were explored for photoelectrodes, and the nature of the two important interfacial events occurring in Ag NC-sensitized solar cells (photoinduced electron transfer and charge recombination) were unveiled by in-depth spectroscopic and electrochemical analyses. This work reveals that the subtle interplay between the light absorbing capability, charge separation dynamics, and charge recombination kinetics in the photoelectrode dictates the solar cell performance. In addition, we demonstrate significant improvement in the photocurrent stability and light conversion efficiency that have not been achieved previously. Our comprehensive understanding of the critical parameters that limit the light conversion efficiency lays a foundation on which new principles for designing Ag NCs for efficient light energy conversion can be built.
36 citations
TL;DR: The ferrocene redox couple has been used as a model redox relay system to investigate photocatalytic properties of CsPbBr3 perovskite nanocrystals and photoinduced interfacial electron transfer occurred with a rate constant of 1.64 X 1010 s-1.
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 vacuu...
35 citations
22 Mar 2019
TL;DR: In this paper, the authors showed that 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.
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.
33 citations
TL;DR: The Halide ion movement in CsPbBr3-xIx gradient films was tracked via absorbance changes in the visible region of the spectrum that enabled us to measure the temperature dependent rate constant and energy of activation of halide ion homogenization.
Abstract: Cesium lead halide perovskite films with a systematic change in the halide composition of CsPbBr3−xIx, in which iodide concentration varies from x = 0 to x = 3, provide a built-in gradient band structure. Such a gradient structure allows for the integrated capture of visible photons and directs them to the energetically low-lying iodide rich region. Annealing gradient halide perovskite films at temperatures ranging from 50 °C to 90 °C causes the films to homogenize into mixed halide perovskites. The movement of halide ions during the homogenization process was elucidated using UV-Visible absorbance and X-ray photoelectron spectroscopy. The halide ion movement in CsPbBr3−xIx gradient films was tracked via absorbance changes in the visible region of the spectrum that enabled us to measure the temperature dependent rate constant and energy of activation (74.5 kJ/mol) of halide ion homogenization. Excited state processes of both gradient and homogenized films probed through transient absorption spectroscopy showed the direct flow of charge carriers and charge recombination in both films.
28 citations
TL;DR: Interestingly, the population and depopulation of the trap states, which are responsible for the changes in both the optical and electronic properties, occur in a different potential/energy regime, thus providing good stability in photoelectrochemical operation.
Abstract: Detailed mechanistic understanding of the optoelectronic features is a key factor in designing efficient and stable photoelectrodes. In situ spectroelectrochemical methods were employed to scrutinize the effect of trap states on the optical and electronic properties of CuI photoelectrodes and to assess their stability against (photo)electrochemical corrosion. The excitonic band in the absorption spectrum and the Raman spectral features were directly influenced by the applied bias potential. These spectral changes exhibit a good correlation with the alterations observed in the charge-transfer resistance. Interestingly, the population and depopulation of the trap states, which are responsible for the changes in both the optical and electronic properties, occur in a different potential/energy regime. Although cathodic photocorrosion of CuI is thermodynamically favored, this process is kinetically hindered, thus providing good stability in photoelectrochemical operation.
16 citations
TL;DR: The excitation of CuI in a CuI/CsPb Br3 film provides synergy between both CuI and CsPbBr3 inating the charge separation and recombination, and prebiasing experiments show the persistent and reversible “memory” effect of electrochemical bias on charge carrier lifetimes.
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 CsPbBr3 in dictating the charge separation and recombination.
11 citations
8 citations
TL;DR: In this paper, the four articles selected for the Energy Spotlight in this issue are just a few examples to show the dynamic nature of metal halide perovskite research, and new inroads are being made to explore new heterostructures and luminescent semiconductor nanoclusters, understand phase stability and offer new insights into excited state processes.
Abstract: As metal halide solar cells reach photoconversion efficiencies over 25%, one question that is often being asked is, “What is next?” Interestingly, there are plenty of new opportunities to explore in the perovskite world. The four articles selected for the Energy Spotlight in this issue are just a few examples to show the dynamic nature of metal halide perovskite research. New inroads are being made to explore new heterostructures and luminescent semiconductor nanoclusters, understand phase stability, and offer new insights into excited state processes. Such advances provide new avenues to further expand the scope of perovskite research, offering new areas to explore.
TL;DR: Energy Selects as discussed by the authors discusses major advances in designing advanced energy materials and their applications in light−energy conversion, and two Perspectives, one by Cotlet and coworkers and the other by Bren and co-workers, have been selected as ACS Editors' Choice articles.
Abstract: Aspart of our editorial advisory board member highlights, we discuss here three articles from the current issue. Of these EAB choice articles, two Perspectives, one by Cotlet and co-workers and the other by Bren and co-workers, have been selected as ACS Editors’ Choice articles. This Energy Selects discusses major advances in designing advanced energy materials and their applications in light−energy conversion.
University of Notre Dame1, Binghamton University2, University of Texas at Austin3, Kyushu University4, University of Bath5, University of California, San Diego6, Pacific Northwest National Laboratory7, Lawrence Berkeley National Laboratory8, Hanyang University9, University of Waterloo10, Texas A&M University11