Can Pb-Free Halide Perovskites be Realized by Incorporating the Neutral or Anionic Molecule?

Exploring Pb-free perovskite alternatives is a major challenge in the current photovoltaic field. Direct substitution of Pb with a non-toxic cation usually lowers the structural or electronic dimension, thereby impacting the excellent photovoltaic properties of halide perovskites. In this work, Pb-free halide perovskites by incorporating the anionic or neutral molecules on the A-site of the perovskite lattice and assess the photovoltaic potential by first-principles calculations is constructed. The Pb-free perovskite CH₄BiCl₃ is predicted to have a direct bandgap within the optimal range for photovoltaic application. Due to the same electronic configuration of B-site Bi³⁺ and Pb²⁺ cations, the CH₄BiCl₃ exhibits a similar electronic band structure with Pb-based halide perovskites. The calculated effective masses and exciton binding energy of electron and hole indicate the high mobility of photogenerated carriers of CH₄BiCl₃. The excellent photovoltaic performance is demonstrated by calculating the spectroscopic limited maximum efficiency, which shows an efficiency of 30.9% for a typical thickness of 0.5 µm. The structural stability of cubic perovskite CH₄BiCl₃ is further evaluated by computing the decomposition energy and ab initio molecular dynamics simulation, demonstrating the thermodynamic stability of CH₄BiCl₃ at room temperature. These results can be a useful guide for exploring novel Pb-free perovskite materials.