Trapped Charges: A Fundamental Cause for Light-Induced Instability in Perovskites

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