Trapped Charges:\nA Fundamental Cause for Light-Induced\nInstability in Perovskites

One of the weakest points in organic–inorganic\nhybrid perovskites\nis their instability against light, which has puzzled the research\nand industry communities despite a lot of efforts conducted so far.\nAlthough how perovskites break down under light illumination has been\nmuch investigated and verified, where chemical degradation occurs\nin the presence of oxygen and moisture, the fundamental cause for\nlight instability in inert conditions remains unclear. A big question\nwith respect to device lifetime is whether a perfect encapsulation\nmethod (ideally, no penetration of moisture and oxygen) will lead\nto long-term stability during an actual energy-harvesting operation.\nIf not, the fundamental cause for light-induced instability needs\nto be thoroughly investigated and prevented technically during device\noperation for their commercialization. In this Perspective, we propose\nthe trapped charges as a fundamental cause of both intrinsic and extrinsic\ndegradation induced by light soaking and even the ion migration observed\nduring the degradation process based on experiments and theoretical\ncalculations as well as revisiting previous studies on degradation.\nAdditionally, practical techniques to suppress charge trapping in\na device will be discussed for the community.