Triple Cross-Linking Engineering Strategies for Efficient and Stable Inverted Flexible Perovskite Solar Cells

Inverted flexible perovskite solar cells (fPSCs) are promising for commercialization due to their low cost, lightweight, and excellent stability. However, enhancing fPSCs' power conversion efficiency and stability remains challenging. Here, an unprecedented triple cross-linking engineering strategy is innovatively exhibit for efficient and stable inverted fPSCs. First, a carefully designed cross-linker, 4-fluorophenyl 5-(1,2-dithiolan-3-yl) pentanoate (FB-TA), is added to the perovskite precursor solution. During the perovskite film's crystallization at a low temperature, the cross-linking product of FB-TA can passivate the grain boundaries and reduce the film's residual strain and Young's module. Then, FB-TA is also introduced for the bottom- and top-interface modification of the perovskite film. The interfacial treating strategy protects the perovskite from water invasion and strengthens the interfaces. The combination of triple strategies affords highly efficient inverted fPSCs with a champion efficiency of 21.42% among the state-of-the-art inverted fPSCs based on nickel oxides. More importantly, the flexible devices also exhibit superior stabilities with T₉₀ >4000 bending cycles, photostability with T₉₀ >568 h, and ambient stability with T₉₀ >2000 h, especially the stability with T₈₀ >1120 h under harsh damp-heat conditions (i.e., 85 °C and 85% RH). The strategy provides new insights into the industrialization of high-performance and stable fPSCs.