Light and Thermally Induced Evolutional Charge Transport in CH₃NH₃PbI₃ Perovskite Solar Cells

Pre-exposure of perovskite solar cells to light or heat can greatly improve their performance, yet the underlying physical mechanisms are still obscure. Herein we systematically investigate the influences of light soaking and thermal phase transition on charge transport dynamics in two-step fabricated CH 3 NH 3 PbI 3 perovskite solar cells. By applying the time-of-flight (TOF) measurement under various light illumination times, we not only confirm the existence of nondispersive charge transport in perovskite solar cells but also directly observe a shallow trap filling process and thus increased charge mobility upon light soaking. We further employ the delay-time-dependent charge extraction by linearly increasing voltage (CELIV) technique to reveal that dispersive bimolecular recombination is also largely inhibited. On the other hand, we conduct temperature-dependent TOF and electrical conductivity studies and surprisingly find a rapid change of both hole and electron mobilities during phase transition from tetragonal to cubic crystalline structures at around 310–330 K until reaching a balance of charge transport.