Discovering layered lead-free perovskite solar absorbers via cation transmutation

For the exploration of stable lead-free perovskites for solar cell applications, we propose a series of Dion-Jacobson (DJ) double perovskites with the formula BDA₂M_IM_IIIX₈ (BDA = 1,4-butanediamine) by substituting two Pb²⁺ in BDAPbI₄ with an M_I⁺ (Na⁺, K⁺, Rb⁺, Cu⁺, Ag⁺, and Au⁺) and M_III³⁺ (Bi³⁺, In³⁺, and Sb³⁺) pair. First-principles calculations demonstrated the thermal stabilities of all the proposed BDA₂M_IM_IIIX₈ perovskites. The electronic properties of BDA₂M_IM_IIIX₈ depend strongly on the choice of M_I⁺ + M_III³⁺ and the structural archetype, and three out of 54 candidates with suitable solar band gaps and superior optoelectronic properties were selected for photovoltaic application. A highest theoretical maximal efficiency of over 31.6% is predicted for BDA₂AuBiI₈. The DJ-structure-induced interlayer interaction of apical I-I atoms is found to play a crucial role in promoting the optoelectronic performance of the selected candidates. This study provides a new concept for designing lead-free perovskites for efficient solar cells.