Ternary‐Metal Sn‐Pb‐Zn Perovskite to Reconstruct Top Surface for Efficient and Stable Less‐Pb Perovskite Solar Cells

Abstract Though Sn‐Pb alloyed perovskite solar cells (PSCs) achieved great progress, there is a dilemma to further increase Sn for less‐Pb requirement. High Sn ratio (>70%) perovskite exhibits nonstoichiometric Sn:Pb:I at film surface to aggravate Sn²⁺ oxidation and interface energy mismatch. Here, ternary metal alloyed (FASnI₃)_0.7(MAPb_1−xZn_xI₃)_0.3 (x = 0–3%) is constructed for Pb% < 30% perovskite. Zn with smaller ionic size and stronger ionic interaction than Sn/Pb assists forming high‐quality perovskite film with ZnI₆⁴⁻ enriched at surface to balance Sn:Pb:I ratio. Differing from uniform bulk doping, surface‐rich Zn with lower lying orbits pushes down the energy band of perovskite and adjusts the interface energy for efficient charge transfer. The alloyed PSC realizes efficiency of 19.4% at AM1.5 (one of the highest values reported for Pb% < 30% PSCs). Moreover, stronger bonding of Zn─I and Sn─I contributes to better durability of ternary perovskite than binary perovskite. This work highlights a novel alloy method for efficient and stable less‐Pb PSCs.