Browsing by Author "Bhosale, Sumit S."

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Functionalization of Graphene Oxide Films with Au and MoOx Nanoparticles as Efficient p-Contact Electrodes for Inverted Planar Perovskite Solar Cells
(2018-09-12)
Bhosale, Sumit S.
;
Jokar, Efat
;
Fathi, Amir
;
Tsai, Cheng-Min
;
Wang, Chi-Yung
A graphene oxide (GO) film is functionalized with metal (Au) and metal-oxide (MoOx) nanoparticles (NPs) as a hole-extraction layer for high-performance inverted planar-heterojunction perovskite solar cells (PSCs). These NPs can increase the work function of GO, which is confirmed with X-ray photoelectron spectra, Kelvin probe force microscopy, and ultraviolet photoelectron spectra measurements. The down-shifts of work functions lead to a decreased level of potential energy and hence increased V-oc of the PSC devices. Although the GO-AuNP film shows rapid hole extraction and increased V-oc, a J(sc) improvement is not observed because of localization of the extracted holes inside the AuNP that leads to rapid charge recombination, which is confirmed with transient photoelectric measurements. The power conversion efficiency (PCE) of the GO-AuNP device attains 14.6%, which is comparable with that of the GO-based device (14.4%). In contrast, the rapid hole extraction from perovskite to the GO-MoOx layer does not cause trapping of holes and delocalization of holes in the GO film accelerates rapid charge transfer to the indium tin oxide substrate; charge recombination in the perovskite/GO-MoOx interface is hence significantly retarded. The GO-MoOx device consequently shows significantly enhanced V-oc and J(sc), for which its device performance attains PCE of 16.7% with great reproducibility and enduring stability.
Mechanism of Photocatalytic CO2 Reduction by Bismuth-Based Perovskite Nanocrystals at the Gas-Solid Interface
(2019-12-25)
Bhosale, Sumit S.
;
Kharade, Aparna K.
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Jokar, Efat
;
Fathi, Amir
;
Chang, Sue-min
We report here a series of nontoxic and stable bismuth-based perovskite nanocrystals (PeNCs) with applications for photocatalytic reduction of carbon dioxide to methane and carbon monoxide. Three bismuth-based PeNCs of general chemical formulas A(3)Bi(2)I(9), in which cation A(+) = Rb+ or Cs+ or CH3NH3+ (MK), were synthesized with a novel ultrasonication top-down method. PeNC of Cs3Bi2I9 had the best photocatalytic activity for the reduction of CO2 at the gas solid interface with formation yields 14.9 mu mol g(-1) of methane and 77.6 mu mol g(-1) of CO, representing a much more effective catalyst than TiO2 (P25) under the same experimental conditions. The products of the photocatalytic reactions were analyzed using a gas chromatograph coupled with a mass spectrometer. According to electron paramagnetic resonance and diffuse-reflectance infrared spectra, we propose a reaction mechanism for photoreduction of CO2 via Bi-based PeNC photocatalysts to form CO, CH4, and other possible side products.
Temperature-Dependent Electroabsorption and Electrophotoluminescence and Exciton Binding Energy in MAPbBr(3) Perovskite Quantum Dots
(2019-08-15)
Rana, Shailesh
;
Awasthi, Kamlesh
;
Bhosale, Sumit S.
;
Diau, Eric Wei-Guang
;
Ohta, Nobuhiro
Organic inorganic lead halide perovskite nanocrystals have attracted much attention as promising materials for the development of solid-state light-emitting devices, but the existence of free or bound excitons or the formation of trap states remains under debate. We recorded temperature-dependent electroabsorption (E-A) and electrophotoluminescence (E-PL) spectra, that is, electric field-induced change in absorption and photoluminescence spectra, for methylammonium lead tribromide (MAPbBr(3)) colloidal perovskite nanocrystals, that is, quantum dots (QD), doped in a poly(methyl methacrylate) film in the temperature range of 40-290 K. Based on the results, the binding energy of the exciton (electron hole pair) was estimated. The exciton binding energy of QD of MAPbBr(3) estimated from the absorption and E-A spectra (similar to 17 meV) is nearly the same as that of a MAPbBr(3) polycrystalline thin solid film, while the exciton binding energy estimated from the temperature-dependent PL spectra (similar to 70 meV) is much greater than that estimated from the absorption profile. The frequency dependence of the E-A intensity observed at 40 and 290 K for the modulated applied electric field indicates a slow ion migration in nanocrystals, which follows the modulation of the applied electric field at a frequency less than 500 Hz. The observed E-A spectra were analyzed with an integral method on assuming the Stark effect; the magnitudes of the changes in electric dipole moment and polarizability following photoexcitation were determined at each temperature from 40 to 290 K. E-PL spectra show that the PL of QD of MAPbBr(3) is quenched on the application of an external electric field; the extent of quenching is much greater for trap emission than for exciton emission. Exciton phonon scattering, which is responsible for the line broadening of the PL spectra, is also discussed based on the temperature-dependent PL spectra.