Interfacial Charge Dynamics in Perovskite Solar Cells Governed by Size of Spherical TiO2 Nanoparticles

초록

Solid-state perovskite solar cells based on methylammonium lead halide have attracted much interest due to their high power conversion efficiency and low fabrication cost. As a means of optimizing the efficiency of the perovskite solar cells, it is desirable to have mesoscopic TiO2 layer with large surface area so that the interfacial area between perovskite and TiO2 increases. In this work, we investigate the charge dynamics at TiO2/perovskite interface in perovskite solar cells where the size of spherical TiO2 nanoparticles (NPs) was controlled in the range of 30 - 65 nm. The NPs of spherical shape make the pores of uniform sizes and greatly improve the contacts and connectivity among the NPs. To examine the effect of NP size on the efficiency of charge transfer from perovskite to TiO2, we measured time-resolved photoluminescence (TR-PL) for FTO/TiO2/CH3NH3PbI3 solar cell devices that employ TiO2 NPs of various sizes. In bare perovskite, the decay of TR-PL intensity arises from radiative relaxation of excited electrons back to the ground state of perovskite. In contrast, at the TiO2/perovskite interface, the TR-PL decay is accelerated by electron transfer from perovskite to TiO2, thereby reflecting the charge transfer dynamics.