Light-Harvesting Lead-Free Mixed Cation Hybrid Halide Perovskites: A Density Functional Theory-Based Computational Screening Study

The popularity of hybrid organic-inorganic perovskite (HOIP) solar cells with a general formula of ABX₃ is on the rise thanks to their remarkable increase in power conversion efficiencies. While the lead-based perovskites have the highest PCEs, environmental concerns about lead and lattice instability of these perovskites under the environmental conditions forced us to find alternative less toxic lead-free perovskites with enhanced environmental stability. In this context, substantial experimental and theoretical efforts have been directed toward the mixing of these three sites (A, B, and X). In this study, a comprehensive computational screening based on density functional theory has been carried out for the mixed cation halide perovskites with a general formula of AA′BX₃ aiming to find promising lead-free candidates. In particular, 23 A/A′-cations, 29 divalent B-ions, and 4 X-anions were employed in the screening, leading to approximately a combination of 29,000 dual-cation perovskites. With the help of empirical tolerance and octahedral factors, this number has been reduced to 2710 perovskites and for each formation energy and band gap computations were completed in three common cubic, orthorhombic, and tetragonal phases. Our computational screening yielded that Sn, In, Hg, Cd, and Ge can be possible candidates for the replacement of Pb, and Cs is the most preferred A/A′ cation, which is followed by HA, NH₄, MA, HA, HY, and FA. Nearly 200 novel perovskites, the majority of which have been proposed in this screening, with suitable formation energies and band gaps could be interesting for further validation through experimental studies.