Hydrolysis-Regulated Chemical Bath Deposition of Tin-Oxide-Based Electron Transport Layers for Efficient Perovskite Solar Cells with a Reduced Potential Loss

The high electron mobility, wide band gap, and chemical stability of n-type SnO2 have facilitated its use as an ideal electron transport layer (ETL) for perovskite solar cells (PSCs). However, the tendency of SnO2 to aggregate during film formation leads to poor morphology and low reproducibility. Despite important advances in the application of SnO2 for PSCs, a thorough understanding of material control over aggregation is lacking. Herein, aggregation-regulated SnO2 films are directly deposited on a fluorine-doped tin oxide glass surface via chemical bath deposition using retarding agents with multiple functional OH groups. Density functional theory calculations confirm the increase in stabilized binding energies of the Sn precursors by the retarding agents. Investigation of the morphology and topography of the SnO2 films reveals that manipulating the physicochemical properties of interacting molecules regulates SnO2 particle aggregation. The chemical states and energy-band properties of the fabricated SnO2 films are found to depend on the retarding agent used in the Sn precursors. The aggregation-regulated SnO2 layer prepared using glycerol exhibits an optimal morphology, a few oxygen vacancies, and a high work-function energy level. A device fabricated using the glycerol–SnO2 film as an ETL achieves a high efficiency of 21.8%, negligible hysteresis, and a reduced potential loss.