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Perovskite-based photovoltaic devices have recently achieved impressively high efficiencies beyond 15% and gained great interest. We show here the formation of perovskite cluster overlayer structures which consist of individual perovskite grains on top of mesoporous TiO2 films, coexisting with the randomly distributed nanocrystals within the films. Perovskite solution concentration was found to play an important role in modulating the perovskite crystallization and cluster overlayer formation process. Absorbance increase in visible wavelength range and shift of photoluminescence (PL) responses of perovskite films due to the effect of precursor concentration change were observed and investigated in detail. The crystallographic analysis of the CH3NH3PbI3 films shows a gradual decrease of the perovskite lattice parameters and shrinkage of unit volume as precursor solution concentration increases, which is correlated to the changes of optical properties. Finally, perovskite-based solar cell device performance was enhanced at higher precursor concentration. [ABSTRACT FROM AUTHOR]

The performance of many emerging compound semiconductors for thin‐film solar cells is considerably lower than the Shockley–Queisser limit, and one of the main reasons for this is the presence of various deleterious defects. A partial or complete substitution of the cations presents a viable strategy to alter the characteristics of the detrimental defects and defect clusters. Particularly, it is hypothesized that double cation substitution could be a feasible strategy to mitigate the negative effects of different types of defects. In this study, the effects of double cation substitution on pure‐sulfide Cu2ZnSnS4 (CZTS) by partially substituting Cu with Ag, and Zn with Cd are explored. A 10.1% total‐area power conversion efficiency (10.8% active‐area efficiency) is achieved. The role of Cd, Ag, and Cd + Ag substitution is probed using temperature‐dependent photoluminescence, time‐resolved photoluminescence, current–voltage (IV), and external quantum efficiency (EQE) measurements. It is found that Cd improves the photovoltaic performance by altering the defect characteristics of acceptor states near the valence band, and Ag reduces nonradiative bulk recombination. It is believed that the double cation substitution approach can also be extended to other emerging photovoltaic materials, where defects are the main culprits for low performance. Double cation substitution in Cu2ZnSnS4 (CZTS) by partially substituting Cu with Ag and Zn with Cd is shown to alter the characteristics of acceptor defects and deep defects responsible for non‐radiative recombination. This synergistic effect of Cd and Ag reflects in power conversion efficiency of 10.1% (10.8% active area) obtained in the (Cu,Ag)2(Zn,Cd)SnS4 system. [ABSTRACT FROM AUTHOR]

Abstract: Kesterite thin film solar cell has been fabricated by chemical spray pyrolysis (CSP) of an aqueous solution followed by high temperature selenization. The pyrolysis formation of Cu2ZnSnS4 was conducted in atmospheric condition with substrate temperature of 280°C. X-ray diffraction and Raman spectroscopy study confirmed the formation of the single phase Cu2ZnSn(S,Se)4 kesterite structure after selenization without traceable secondary phases. FESEM image shows a uniform absorber layer without carbon layer formed between CZTSSe and Mo. Power conversion efficiency of 5.1% was obtained with different amounts of selenium incorporation. Power dependent and temperature dependent photoluminescence (PL) study revealed donor-to-acceptor pairs (DAP) transition at low temperature. Severe PL quenching at temperatures above 41K is attributed to the opening of non-radiative recombination channels from the defects associated with non-stoichiometric elemental ratio. Therefore, further enhancement of power conversion efficiency can be achieved by better control of stoichiometry. [Copyright &y& Elsevier]