Non-toxic and rapid chemical bath deposition for SnO2 electron transporting layers in perovskite solar cells

Perovskite solar cells are a promising new 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 non-toxic sodium stannate solutions. Within 6 minutes 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 Sn(II) doping assumption required for n-doping & 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 other thin-film metal oxide coatings (MoOx, SiO2) and beneficial for devices such as solar cells, photodetectors, light emitting diodes, and heterogeneous catalysis.