Bifunctional Surface Engineering on SnO2 Reduces Energy Loss in Perovskite Solar Cells

Tin oxide (SnO2) has recently emerged as a promising electron transport layer for perovskite solar cells (PSCs) in light of the material's optical and electronic properties and its low-temperature processing. However, SnO2 films are prone to surface defect formation, which results in energy loss in PSCs. We report that surface treatment using ammonium fluoride (NH4F) leads to reduced surface defects and that it also induces chemical doping of the SnO2 substrate simultaneously. The effects of NH4F treatment on SnO2 properties are revealed by surface chemical analysis, computational studies, and energy level investigations, and PSCs with the treatment achieve photovoltaic performance of 23.2% in light of higher voltage than in relevant controls.