Thermal-evaporated selenium as a hole-transporting material for planar perovskite solar cells

A hole-transporting layer is essential for effective operation of planar perovskite solar cells. Hole-transporting materials (HTMs) used so far are mainly based on organic semiconductors, which are usually expensive and relatively instable compared with inorganic materials. In this article, crystalline selenium (c-Se) prepared by thermal evaporation followed by annealing at low temperature was used as the hole-transporting layer for the planar perovskite solar cells in the device structure of fluorine-doped tin oxide (FTO)/SnO2/perovskite/selenium/Au. The device employing c-Se as HTM displayed enhanced long-term stability, keeping 80% of the original efficiency after 40 days in ambient environment. However, the power conversion efficiency of 8.3% remains low compared with the device based on spiroOMeTAD, which results from higher recombination in the c-Se device as determined by impedance spectroscopy. Thermal-evaporated selenium could be a low-cost and easy-fabrication HTM for efficient and stable perovskite solar cells after reducing the recombination in devices.