Precise synthesis and characterization of lead-free organic bismuth halide MA₃Bi₂I_xCl_9-x (x = 3) and FA₃Bi₂I_xCl_9-x (x = 3) perovskite towards photovoltaic applications

Bismuth halide perovskites shows excellent replacement of Lead due to safer with high chemical stability and exhibits similar optoelectronic properties. Experimental examinations have been done only for MA₃Bi₂I₉ and FA₃Bi₂I₉ compounds which had only one halide. Herein, we investigated MA₃Bi₂I_xCl_9-x (x = 3) (labelled as MBI_xCl_9-x) and FA₃Bi₂I_xCl_9-x (x = 3) (labelled as FBI_xCl_9-x) lead free perovskites with mixed halides for photovoltaic applications. By incorporating the Cl^- halide anion into the MBI_xCl_9-x (x = 3) and FBI_xCl_9-x (x = 3) led to remains unchanged crystal structure and enhancement of the surface morphology of the thin films. Increasing the absorption in visible region of MBI_xCl_9-x (x = 3) and FBI_xCl_9-x (x = 3) are 628 nm and 650 nm with lowering the band gap of 1.85 V and 1.56 eV respectively. The prominent photo emission spectra are obtained at 654 nm and 658 nm for MBI_xCl_9-x (x = 3) and FBI_xCl_9-x (x = 3) respectively which reducing the rate of recombination. The thermal stability of both perovskites is investigated, up to 230^ᵒ C and 232^ᵒ C could sustained without weight loss occurs. Nyquist plot confirmed that MBI_xCl_9-x (x = 3) perovskite have higher recombination resistance R_rec value than FBI_xCl_9-x (x = 3) which led to the reduction of rate of recombination of charge carriers at interface layers. MBI_xCl_9-x (x = 3) and FBI_xCl_9-x (x = 3) perovskites solar cells has produced Power Conversion Efficiency (PCE) of 0.078 % and 0.016 % with open circuit voltage (V_oc) of 0.410 V and 0.239 V, short circuit current density (J_sc) of 0.623 mA/cm² and 0.234μA/cm² respectively.