Lead-free layered Aurivillius-type Sn-based halide perovskite Ba2X2[Csn−1SnnX3n+1] (X = I/Br/Cl) with an optimal band gap of ∼1.26 eV and theoretical efficiency beyond 27% for photovoltaics

Abstract

Sn-based perovskite solar cells (PSCs) have shown great advantages as capable alternatives to poisonous Pb-based PSCs, with impressive certified power conversion efficiencies (PCE) beyond 14%. However, their poor stability induced by oxidation has hindered the further development of Sn-based PSCs. Herein, through first-principles calculations, inorganic layered Aurivillius-type Sn-based halide perovskites Ba₂X₂[Cs_n−1Sn_nX_3n+1] (X = I/Br/Cl) have been designed, in which the [Ba₂X₂] layer blocks the oxygen in air, enhancing the inoxidizability of the crystals. Ba₂X₂[Cs_n−1Sn_nX_3n+1] exhibit direct band gaps (0.84–2.20 eV), satisfying the requirements for single- and multi-junction PSCs. As the best candidate, Ba₂Br₂[Cs₂Sn₃Br₁₀] has an optimal band gap (1.26 eV), high carrier mobility (135–173 cm² V⁻¹ s⁻¹) and desirable absorption coefficient (∼10⁵ cm⁻¹). Consequently, the optimized single-junction SnO₂/Ba₂Br₂[Cs₂Sn₃Br₁₀]/CuSbS₂ shows a record PCE of 27.7% among Sn-based PSCs, beyond the champion PCE of Pb-based PSCs (25.5%). These energetic results provide a new perspective to improve the performance of Sn-based single-junction PSCs and give a potential alternative to bottom/top PSCs in tandem devices.