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

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 TiCT 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.