Exploring wide bandgap metal oxides for perovskite solar cells

The heterojunction formed when wide bandgap oxides come into contact with perovskite solar cells is essential for high efficiency as it minimizes charge leakage along with charge separation and charge transfer. Therefore, the electrical and optical properties of wide bandgap oxides, including the bandgap, charge mobility, and energy level, directly determine the efficiency of perovskite solar cells. In addition, the surface properties of the wide bandgap oxide act as an important factor that determines the efficiency through the wettability and penetration of the precursor solution during perovskite layer deposition and long-term stability through the intimate interfacial bonding with the perovskite. Although a great variety of wide bandgap oxides are known, the number that can be used for perovskite solar cells is considerably reduced in view of the limitations that the light absorber (here, perovskite) for solar cells is fixed, and the oxides must be uniformly coated at low temperature onto the substrate. Herein, a review of the results from several broad bandgap oxides used in perovskite solar cells is presented, and a direction for discovering new photoelectrodes is proposed.