Improved Photogenerated Charge Carriers in CsPbBr₃ Perovskite Device

CsPbBr₃ perovskites have attracted attention in photovoltaic applications due to their long-term stability and broad absorption band. However, solar cell devices fabricated using this material have produced low power conversion efficiency (PCE) due to the large bandgap (2.3 eV) limiting its electrical conductivity. In this work, partial substitution of cations is done to alter the optical, structural, and electrical characteristics of CsPbBr₃ perovskite using a two-step solution-based deposition method. At low annealing temperatures, crystallization is observed as the Cs⁺ cation is substituted with methylammonium iodide (MAI). Small grains and poor surface coverage are observed for the CsPbBr₃ perovskite. The partial substitution of Cs⁺ to produce a double-cation perovskite facilitated an increase in grain size and pinhole-free morphology. Optical characteristics were improved as observed by the decrease in bandgap from 2.31 eV (CsPbBr₃) to 1.70 eV in the MA_0.6Cs_0.4PbBr₃ material. The small radius of Cs⁺ in MACsPbBr₃ maintains a low effective radius in the perovskite material. It thus maintains the orthorhombic crystal structure of CsPbBr₃ as confirmed by X-ray diffraction. Space-charge-limited current measurements revealed an increase in electron mobility and low trap density in FTO/TiO₂/MA_0.6Cs_0.4PbBr₃/Pd electron-only device as a result of pinhole-free morphology minimizing trap-assisted recombination, and improved surface coverage as compared to the pristine device. The double-cation electron-only device achieved a PCE of 5.2% while the pristine device achieved a PCE of 3.4%, maintaining 80% of their PCE for 48 and 58 hours, respectively. These findings offer a pathway to improve the electrical conductivity of CsPbBr₃-based perovskite material.