Effect of chloride substitution on interfacial charge transfer processes in MAPbI ₃ perovskite thin film solar cells: planar versus mesoporous†

Abstract

For photovoltaic devices based on hybrid organic–inorganic perovskite thin films, the cell architecture is a vital parameter in defining the macroscopic performance. However, the understanding of the correlation between architecture and carrier dynamics in perovskite thin films has remained elusive. In this work, we utilize concerted materials characterization and optical measurements to investigate the role of chloride addition in PSC devices with two different architectures. Perovskite thin films, prepared with varying ratios of methylammonium halide MACl : MAI (0 : 1, 0.5 : 1, 1 : 1, and 2 : 1), were coated on either planar or mesoporous TiO ₂/FTO substrates. X-ray diffraction analysis reveals that with increasing the ratio of the Cl ⁻ precursor, there is an increasing preferential directional growth of the perovskite film in both configurations. Time-resolved photoluminescence spectroscopy was applied to investigate the electron injection dynamics from the photoexcited perovskites to the TiO ₂. It is found that the interfacial electron injection rate from perovskite to planar TiO ₂ is accelerated with increasing Cl ⁻ content, which explains the increased power conversion efficiencies using Cl ⁻-modified perovskites as photoactive materials. In contrast, Cl ⁻ addition demonstrate no discernable influence on electron injection to mesoporous TiO ₂, suggesting the interfacial charge recombination rather than electron injection give rise to the improved performance observed in the mesoporous configuration. The results presented here, provide a deeper understanding of the mechanism of chloride addition to MAPbI ₃ solar cells with different architectures.

Abstract

Electron injection from perovskite to planar TiO ₂ accelerates with chloride addition, in mesoporous TiO ₂ carrier recombination is slowed.