Charge Transfer and Diffusion at the Perovskite/PCBM Interface Probed by Transient Absorption and Reflection

Interfacial charge transfer (CT) and diffusion are crucial processes that largely affect the device performance of perovskite solar cells. Here, we investigated the interfacial charge transfer and diffusion in the CH3NH3PbI3/PCBM film by ultrafast transient absorption (TA) and transient reflection (TR) spectroscopies. A subpicosecond CT coupled with carrier diffusion and hot carrier cooling is observed, which is almost independent of temperature. It is also found that the interfacial CT is slowed down to 11 ps in a thinner perovskite film. A diffusion-based model is further built to fit the TR dynamics, and we find that the more significant surface recombination in thinner films can compete with interfacial CT, which lowers CT efficiency.