Inorganic p-type contact materials for perovskite-based solar cells

Organic-inorganic hybrid perovskite solar cells are promising low-cost emerging photovoltaic devices due to their rapid progresses in conversion efficiencies. In this perspective, we review recent published works of perovskite-based solar cells incorporated with an inorganic p-type hole transport layer. The current state-of-the-art devices of nickel oxide-based perovskite solar cells display a remarkable power of efficiency over 15%. In addition, solar cells using perovskite as light absorber and hole transporter without p-type contact material are also reviewed.