Towards Efficiency Improvements for Non-toxic Perovskite Solar Cells

Organic-inorganic metal-halide perovskites are promising materials for solar cells due to their high optical absorption, ambipolar charge transport, tunable band gap, earth-abundant materials, and low-cost processing. While perovskite solar cells (PSCs) are expected to dramatically reduce solar module costs, commercialization requires improved device lifetimes and the replacement of environmentally-toxic Pb cations. Sn cations offer a similar bandgap to Pb, and preliminary data suggest that Sn-based cells have higher theoretical power conversion efficiency (PCE). However, Sn cations have received little research attention and the PCE of Sn-based cells remains less than a third of Pb-based cells. Here, we report synthesis, processing, and characterization of Sn-based PSCs by spin coating titania (TiO ₂ ), methylammonium tin iodide perovskite (CH ₃ NH ₃ SnI ₃ ), and an organic hole transporting material (Spiro-OMeTAD) onto transparent conducting oxide substrates. A greater understanding of structure-processing relationships is expected to improve solar cell performance.