Effect of Single-Crystal TiO₂/Perovskite Band Alignment on the Kinetics of Electron Extraction

The kinetics of electron extraction at the electron transfer layer/perovskite interface strongly affects the efficiency of a perovskite solar cell. By combining transient absorption and time-resolved photoluminescence spectroscopy, the electron extraction process between FA_0.83Cs_0.17Pb(I_0.83Br_0.17)₃ and TiO₂ single crystals with different orientations of (100), (110), and (111) were probed from subpicosecond to several hundred nanoseconds. It was revealed that the band alignment between the constituents influenced the relative electron extraction process. TiO₂(100) showed the fastest overall and hot electron transfer, owing to the largest conduction band and Fermi level offset compared to FA_0.83Cs_0.17Pb(I_0.83Br_0.17)₃. It was found that an early electron accumulation in these systems can have an influence on the following electron extraction on the several nanosecond time scale. Furthermore, the existence of a potential barrier at the TiO₂/perovskite interface was also revealed by performing excitation fluence-dependent measurements.