Regulating TiO₂ Deposition Using a Single-Anchored Ligand for High-Efficiency Perovskite Solar Cells

Planar perovskite solar cells (PSCs), as a promising photovoltaic technology, have been extensively studied, with strong expectations for commercialization. Improving the power conversion efficiency (PCE) of PSCs is necessary to accelerate their practical application, in which the electron transport layer (ETL) plays a key part. Herein, a single-anchored ligand of phenylphosphonic acid (PPA) is utilized to regulate the chemical bath deposition of a TiO₂ ETL, further improving the PCE of planar PSCs. The PPA possesses a steric benzene ring and a phosphoric acid group, which can inhibit the particle aggregation of the TiO₂ film through steric hindrance, leading to optimized interface (ETL/perovskite) contact. In addition, the incorporated PPA can induce the upshift of the Fermi-level of the TiO₂ film, which is beneficial for interfacial electron transport. As a consequence, the PSCs with PPA-TiO₂ achieve a PCE of 24.83%, which is higher than that (24.21%) of PSCs with TiO₂. In addition, the unencapsulated PSCs with PPA-TiO₂ also exhibit enhanced stability when stored in ambient conditions.