A 0D Additive for Flexible All-Inorganic Perovskite Solar Cells to Go Beyond 60 000 Flexible Cycles

All-inorganic cesium lead halide flexible perovskite solar cells (f-PSCs) exhibit superior thermal stability compared to their organic-inorganic hybrid counterparts. However, their flexibility and efficiency are still below-par for practical viability. Herein, a design using a 0D Cs4Pb(IBr)(6) additive to transform tensile stress into compressive stress in the perovskite film, effectively preventing expansion of cracks for significantly improved mechanical durability, is reported. It is found that not only is improved flexibility obtained, but also the cell efficiency is increased for the all-inorganic flexible 3D CsPbI3-xBrx solar cells. The CsPbI2.81Br0.19 f-PSC retains over 97% of its initial efficiency even after 60 000 flexing cycles at a curvature radius of 5 mm (R = 5 mm). Simultaneously, 0D Cs4Pb(IBr)(6) enhances the crystallinity of the CsPbI2.81Br0.19 film and passivates the defects along the grain boundaries, effectively improving the photovoltaic performance of the all-inorganic f-PSCs. The highest power-conversion efficiency obtained is 14.25% with a short-circuit current density of 18.47 mA cm(-2), open-circuit voltage of 1.09 V, and fill factor of 70.67%. This strategy paves the way for further improvement of the mechanical durability of all-inorganic f-PSCs.