Direct Visualization of Interfacial Charge Transfer in CsPbBr3 Perovskite Solar Cells Using Pattern-Illumination Time-Resolved Phase Microscopy

Abstract

This study follows our previous investigation of charge carrier dynamics at the hole transport layer (HTL)/perovskite (CsPbBr₃) interface, where pattern-illumination time-resolved phase microscopy (PI–PM) revealed that HTLs significantly influence hole extraction and charge recombination processes. In the absence of an HTL, CsPbBr₃ exhibited dominant hole dynamics, which were mitigated by the introduction of Spiro-OMeTAD and P3HT, with the latter showing superior hole extraction efficiency. In this follow-up study, we extend our analysis to electron transport layers (ETLs) and the full ETL/perovskite/HTL structure, and investigate modulation of charge separation at interfaces. Our results show that TiO₂, a widely used ETL, enhances electron extraction but still exhibits recombination due to interfacial states. Li and Pt doping further improve charge separation, with Pt-doped TiO₂ demonstrating the most significant reduction in recombination and the longest charge carrier lifetimes. When combined with HTLs, the choice of HTL significantly impacts charge extraction: P3HT facilitates more efficient hole removal than Spiro-OMeTAD. The most effective configuration for charge separation and suppression of residual charge carriers was achieved with Pt-doped TiO₂ as the ETL and P3HT as the HTL. These findings provide a comprehensive understanding of charge carrier transport in inorganic perovskite solar cells, demonstrating the importance of both ETL and HTL selection for optimizing photovoltaic performance.