Light Soaking Induced Halide Doping of Evaporated Spiro‐OMeTAD in Perovskite Solar Cells

Abstract Identification and investigation of light soaking effect (LSE) as well as the associated physical mechanisms are crucial for achieving reliable power output and high stability of solar cells. Here, a profound LSE dependence on doping status of organic hole transport materials (HTMs) in perovskite solar cells is demonstrated. A tenfold efficiency enhancement is realized in the devices based on evaporated undoped HTMs caused by LSE. This light‐soaking behavior is attributed to the increased film conductivity, enhanced built‐in potential at perovskite/HTM interface, reduced interfacial charge accumulation, and suppressed nonradiative recombination in devices. Besides, chemical and structural analysis reveal that halide ions migration and subsequent photodoping of organic HTMs enables significant improvement of the film conductivity and hole mobility. Moreover, the HTM mobilities are proven to determine the LSE strength and kinetics, causing significant variation in photostability of devices.