Dynamic Photochromic\nSwitching Enables Efficient and\nUV-Resistant Perovskite Solar Cells

Ultraviolet (UV) irradiation is one of the key factors\naffecting\nthe stability of perovskite solar cells (PSCs), yet completely shuttering\nUV light would degrade the current output of the devices. Thus improving\nUV stability without loss of current generation remains challenging\nto date. Herein, we report a simple methodology by incorporating a\nphotochromic diarylethene (6F) molecule into the perovskite film,\nwhich simultaneously improves the efficiency and UV stability of PSCs.\nWe unearth two distinct degradation routes for PSCs under UV irradiation:\nperovskites into precursor components or the α-phase to δ-phase\ntransition, followed by decomposition into precursor components. We\nfurther reveal that the dynamic photochromic effect of 6F under irradiation\ninduces UV protection of the perovskite film by completely shutting\ndown the latter route, which significantly improves the UV stability\nof PSCs. Additionally, hydrogen bonding between 6F and perovskite\nlead to the passivation of defects in the lattice, eventually giving\na power conversion efficiency (PCE) of 24.18% compared with the control\ndevice (22.14%), which is among the highest PCEs for inverted PSCs\nvia a two-step solution method. We believe this methodology can offer\na new avenue toward fabricating efficient and stable PSCs.