Mesoporous SnO₂ single crystals as an effective electron collector for perovskite solar cells.

Mesoporous single crystals are prized for their fast electron transport and high surface area. Here we report the first synthesis of mesoporous SnO2 single crystals (SnO2 MSCs) by a simple silica-templated hydrothermal method, and its application in solution-processed perovskite solar cells (PSCs). A relatively low efficiency (3.76%) was obtained due to the strong charge recombination at the SnO2/perovskite interface. However, by coating a thin TiO2 barrier layer on SnO2via TiCl4 treatment, we were able to achieve an 8.54% power conversion efficiency (PCE). A dynamics study using impedance spectroscopy revealed a much lower transport resistance for the SnO2 MSC-based solar cells than for the TiO2 nanocrystal PSCs, but a stronger recombination. Significantly, the thin TiO2 coating layer on SnO2 considerably reduced the recombination while largely maintaining the superior electron-transport properties.