Improved interfacial adhesion for stable flexible inverted perovskite solar cells

Flexible perovskite solar cells have attracted widespread attention due to their unique advantages in lightweight, high flexibility, and easy deformation, which are suitable for portable electronics. However, the inverted (p-i-n) structured devices suffer from poor stability largely due to the low adhesion at the brittle interface (the hole transport layer/perovskite). Herein, zeolitic imidazolate framework-67 (ZIF-67) is applied to inverted structured cells to optimize the interface and prolong the device lifetime. As a result, the flexible devices based on ZIF-67 obtain the champion power conversion efficiency of 20.16%. Over 1000 h under continuous light irradiation, the device retains 96% and 80% of its original efficiency without and with bias, respectively. Notably, devices show mechanical endurance with over 78% efficiency retention after 10,000 cycles of consecutive bending cycles (R = 6 mm). The introduction of ZIF-67 suppresses the cracking in device bending, which results in improved environmental stability and bending durability.