Synergistic Modification of 2D Perovskite with Alternating Cations in the Interlayer Space and Multisite Ligand toward High‐Performance Inverted Solar Cells

The preparation of high-quality perovskite films is key to realize efficient and stable inverted perovskite solar cells. The trap-assisted nonradiative recombination at grain boundary (GB) and surface poses a serious challenge for fabricating high-quality perovskite films. Here, a synergistic modulation strategy of two-dimensional (2D) perovskite with alternating cations in the interlayer space (ACI) and multisite ligand 2-mercapto-1,3,4-thiadiazole (MTD) for fabricating high-quality methylammonium-free perovskite films is reported. The formation of ACI 2D perovskite promotes the nucleation of three-dimensional (3D) perovskites, suppresses the generation of yellow phase, and promotes the formation of black phase, leading to increased grain size and crystallinity. Due to the synergistic effect of ACI 2D perovskite and MTD, the defects at GBs and surface are healed simultaneously. The significantly inhibited nonradiative recombination enables realization of high-efficiency inverted devices with a fascinating power conversion efficiency (PCE) of 24.58%, which is one of the highest PCEs reported for inverted devices. The synergistically modified unsealed device demonstrates an excellent long-term ambient stability, retaining 90.5% of its initial PCE after 3000 h under a relative humidity of 30-40%. This work provides deep insights into minimizing nonradiative recombination losses through the rational synergistic engineering of GB and surface toward efficient and stable inverted devices.