Low‐Temperature‐Processed CdS as the Electron Selective Layer in an Organometal Halide Perovskite Photovoltaic Device

Organic–inorganic halide perovskites have recently been crowned as the leading next‐generation photovoltaic material due to their high efficiency and simple fabrication process. Herein, a low‐temperature‐processed CdS thin film (commonly used as a buffer layer in commercial CdTe or CIGSe solar cells) is reported as an electron selective layer in perovskite devices based on the following reasons: First, the photoelectric property of CdS thin film is investigated, illustrating the possibility of CdS as the electron selective layer in the application of methylammonium lead (II) iodide perovskite devices. More specifically, CdS semiconductor film presents a higher mobility compared with traditional TiO 2 thin film, which benefits the electron extraction and transmission; second, it is found that the perovskite thin film spun‐coating on the CdS substrates grows with an obvious tendency along the direction toward the thickness of thin film, which reduces the chance of recombination of electrons and hole, beneficial to their separation. It is also revealed that the perovskite‐device‐based CdS electron selective layer has a higher stability compared with that of TiO 2 due to the difference of substrates wetting.