Electron Transport Layer-Free Ruddlesden–Popper Two-Dimensional Perovskite Solar Cells Enabled by Tuning the Work Function of Fluorine-Doped Tin Oxide Electrodes

Abstract

Organic–inorganic halide two-dimensional (2D) layered perovskites have been demonstrated to have better environmental stability than conventional three-dimensional perovskites. In this study, we investigate the fabrication of electron transport layer (ETL)-free Ruddlesden–Popper 2D perovskite solar cells (PSCs) by tuning the work function of a fluorine-doped tin oxide (FTO) electrode. With the deposition of polyethylenimine (PEIE) onto its surface, the work function of the FTO electrode could be raised from −4.72 to −4.08 eV, which is more suitable for electron extraction from the perovskite absorber. Using this technique, the ETL-free 2D PSCs exhibited an excellent power conversion efficiency (PCE) of 12.7% (on average), which is substantially higher than that of PSCs fabricated on a pristine FTO electrode (9.6%). Compared with the PSCs using TiO2, the ETL-free PSCs could be fabricated under a low processing temperature of 100 °C with excellent long-term stability. After 15 days, the FTO/PEIE-based ETL-free PSCs showed a PCE degradation of 16%, which is significantly lower than that of the TiO2-based case (29%). The best-performing PSC using a FTO/PEIE cathode showed a high PCE of 13.0%, with a small hysteresis degree of 2.3%.