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

Abstract

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 0.83 Cs 0.17 Pb(I 0.83 Br 0.17 ) 3 and TiO 2 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. TiO 2 (100) showed the fastest overall and hot electron transfer, owing to the largest conduction band and Fermi level offset compared to FA 0.83 Cs 0.17 Pb(I 0.83 Br 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 TiO 2 /perovskite interface was also revealed by performing excitation fluence-dependent measurements.

Charge Transfer Kinetics in Halide Perovskites: On the Constraints of Time-Resolved Spectroscopy Measurements

“…Furthermore, if an electric barrier exists for charge transfer at the CTL/perovskite interface, often the excitation wavelength or the fluence should be varied to overcome it. The latter case is shown in Figure where at lower fluences no electron transfer can be observed in a TiO 2 /perovskite assembly (Figure A,B) . As the excitation fluence increases further, electrons accumulate at the conduction band due to the band-filling effect.…”

“…As the excitation fluence increases further, electrons accumulate at the conduction band due to the band-filling effect. This electron accumulation can overcome the electric barrier at the CTL/perovskite interface and initiate electron transfer (Figure C) …”

“…The excitation of the samples was at 467 nm, and the decay traces were monitored at 750 nm. Extended data from ref ( 95 ).…”

“…The latter case is shown in Figure 9 where at lower fluences no electron transfer can be observed in a TiO 2 /perovskite assembly ( Figure 9 A,B). 95 As the excitation fluence increases further, electrons accumulate at the conduction band due to the band-filling effect. This electron accumulation can overcome the electric barrier at the CTL/perovskite interface and initiate electron transfer ( Figure 9 C).…”

“…This electron accumulation can overcome the electric barrier at the CTL/perovskite interface and initiate electron transfer ( Figure 9 C). 95 …”