Effect of halide-mixing on tolerance factor and charge-carrier dynamics in (CH₃NH₃PbBr_3-xCl_x) perovskites powders

This work demonstrates a route to making mixed halide perovskite powders at room temperature by the anti-solvent-assisted crystallization method. Although, mixed halide CH₃NH₃PbBr_3−xCl_x perovskites have been prepared by different methods, however, to the best of our knowledge the anti-solvent-assisted crystallization method is employed here for the first time to prepare mixed halide CH₃NH₃PbBr_3−xCl_x perovskite powders. Solution-processed methyl ammonium lead tribromide CH₃NH₃PbBr₃ (x = 0) and different amounts of chloride (Cl) containing mixed halide perovskites (CH₃NH₃PbBr_3−xCl_x) were prepared for compositions of x = 0.5, 1, 1.25, 1.75. It reveals that bulk CH₃NH₃PbBr_3−xCl_x samples are highly crystalline and exists in pure single cubic phase with an increased tolerance factor as compared to pure CH₃NH₃PbBr₃. The CH₃NH₃PbBr₃ perovskite has space-group Pm-3 m and a cell parameter of 5.930 Å (volume = 206 Å). The synthesis route adopted here gives access to hybrid perovskites powders with high Cl content and hence enables the band gap to be precisely tuned over a range from 2.26 to 2.49 eV. The powder samples display the subtle shifts in the emission spectra and the photoluminescence kinetics exhibits a decrease in average lifetime by increasing the Cl contents due to the presence of trap states in the structures that encourage non-radiative recombination of charge carrier. Conventionally, the CH₃NH₃PbBr₃-based inverted solar cell architecture is prepared via mixing of the CH₃NH₃Br and PbBr₂ precursors. In contrast, herein, the precursor solutions are directly prepared from the CH₃NH₃PbBr₃ powder and the active layer of the inverted perovskite solar cells are then spin coated using this solution. The high V_oc value of the fabricated solar cells potentially makes it a promising candidate for tandem photovoltaic, photocatalytic water splitting, and semi-transparent photovoltaic applications.