Low Temperature Producing Copper‐Doped Gallium Oxide as Hole Transport Layers of Perovskite Solar Cells Enhanced by Impurity Levels

In inverted perovskite solar cells (PSCs), metal oxides become kind of promising hole transport layers for their facile synthesis and low cost. For conventional hole transport materials, the valence band match between metal oxides and perovskite layers is usually necessary for the hole extraction process. Ga 2 O 3 is an emerging semiconductor material with ultrawide bandgap, but a significant energy level mismatch exists at Ga 2 O 3 /perovskite interfaces. In this work, Cu‐doped Ga 2 O 3 (Ga 2 O 3 :Cu) nanocrystals are synthesized by the hydrothermal method and used as the hole transport material of inverted PSCs for the first time. It is found that Cu dopants can substantially improve the performance of Ga 2 O 3 layers, and the efficiency of PSCs is increased from 7.6% to 19.5%. This improvement can be attributed to the additional hole transport channels from impurity levels of Cu dopants, which exactly match with the valence band of perovskite layers. As a consequence, Ga 2 O 3 :Cu layers can effectively extract holes and inhibit the recombination in perovskite layers. This work also provides an alternative route for the design of hole transport materials.