Review of Inorganic Hole Transport Materials for Perovskite Solar Cells

In the last decade, perovskite solar cells have witnessed great progress with a certified photoelectric conversion efficiency of 25.7%, which is comparable to single-crystal silicon solar cells, but the stability issue still restricts commercialization. As a solution to stability improvement, inorganic hole transport materials (HTMs) are widely studied due to their excellent stability compared to traditional organic HTMs, as well as low fabrication cost and high conductivity. Herein, the intrinsic properties of widely studied inorganic p-type materials for HTMs, their fabrication methods, and the progress that has been made with them are summarized. In addition, the cost of various inorganic HTMs is also discussed.