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.