Localized effect of PbI2 excess in perovskite solar cells probed by high-resolution chemical–optoelectronic mapping

Abstract

We report the laser irradiation of CH₃NH₃PbI₃ solar cells to generate and control localized PbI₂ degradation product. We show that by tuning the laser power and illumination time, we can controllably form a local excess of PbI₂. High-resolution advanced multi-mapping techniques are used to highlight the effect of PbI₂ on the photophysical and photoelectrical properties in a complete perovskite device. Whereas a thick PbI₂ film at the perovskite/hole transport layer interface has a detrimental effect on the photocurrent and photoluminescence, a thin PbI₂ film (<20 nm) leads to a significant photocurrent increase, which is ascribed to the passivation of non-radiative defects and reduced charge recombination at the interface. Our findings reveal that laser irradiation is a new approach to understand the effect of PbI₂ surface layers and potentially offers a means to passivate trap states and improve PV properties of perovskite devices.