Efficient Ideal‐Bandgap Tin–Lead Alloyed Inorganic Perovskite Solar Cells Enabled by Structural Dimension Engineering

Abstract Inorganic tin–lead alloyed perovskite solar cells with optimal bandgap have gained increasing attention because of their higher theoretical efficiency limit, inherently robust stability, and potentials in all‐inorganic perovskite tandems. However, their efficiency has far lagged from their Pb‐based counterparts owing to some intractable problems such as poor crystallization and facile Sn 2+ oxidation. Here, a small amount of 2D perovskite PEAPb 0.7 Sn 0.3 I 4 is utilized to regulate the crystallization process of 3D CsPb 0.7 Sn 0.3 I 3 based on the temperature‐gradient annealing method. The X‐ray diffraction results show that a stable intermediate phase composed of 3D perovskite seeds and 2D phases is formed under a lower annealing temperature of 50 °C, and the pre‐crystallized 3D perovskites can promote the subsequent crystallization upon 80 °C annealing to attain high quality film. It is interesting that the 2D perovskite phase is ultimately mainly located between the 3D perovskite phase and hole transport layer as revealed by the time of flight‐secondary ion mass spectrometry. The resulting perovskite exhibits a lower extent of non‐radiative recombination and better stability. Consequently, the device achieves a champion efficiency of 14.6% setting a new record for inorganic tin‐lead perovskite solar cells (PSCs). This work sheds more light on the future progress of inorganic tin‐lead PSC.