High‐Performance Ideal Bandgap Sn‐Pb Mixed Perovskite Solar Cells Achieved by MXene Passivation

Abstract Ideal bandgap (1.3–1.4 eV) Sn‐Pb mixed perovskite solar cells (PSC) hold the maximum theoretical efficiency given by the Shockley–Queisser limit. However, achieving high efficiency and stable Sn‐Pb mixed PSCs remains challenging. Here, piperazine‐1,4‐diium tetrafluoroborate (PDT) is introduced as spacer for bottom interface modification of ideal bandgap Sn‐Pb mixed perovskite. This spacer enhances the quality of the upper perovskite layer and forms better energy band alignment, leading to enhanced charge extraction at the hole transport layer (HTL)/perovskite interface. Then, 2D Ti ₃ C ₂ T _x MXene is incorporated for surface treatment of perovskite, resulting in reduced surface trap density and enhanced interfacial electron transfer. The combinations of double‐sided treatment afford the ideal bandgap PSC with a high efficiency of 20.45% along with improved environment stability. This work provides a feasible guideline to prepare high‐performance and stable ideal‐bandgap PSCs.