Nontoxic and Rapid Chemical Bath Deposition for SnO₂ Electron Transporting Layers in Perovskite Solar Cells

Perovskite solar cells are a promising solar technology with efficiencies surpassing polycrystalline silicon solar cell technology. For the n-i-p perovskite solar cells, tin oxide is typically used as the electron transport layer. One typical deposition method is chemical bath deposition. However, the drawbacks are toxic precursors and the slow reaction driven by dissolved oxygen forming SnO2–x. Here, we present a tin oxide chemical bath deposition starting from nontoxic sodium stannate solutions. Within 6 min of reaction time, a 9 nm thick amorphous Sn(IV) oxide film is grown, yielding solar cells with power conversion efficiencies of at least 23.2%. Surprisingly, the sole use of Sn(IV) precursors contradicts the previous assumption on Sn(II) required for n-doping and high electric conductivity, and, unexpectedly, amorphous tin oxide films are as suitable for charge transport layers as their crystalline counterparts. The synthesis method is transferrable to other substrates (ITO, glass) and beneficial for devices such as solar cells, photodetectors, light-emitting diodes, and heterogeneous catalysis.