Near‐Infrared Photoresponse of One‐Sided Abrupt MAPbI3/TiO2 Heterojunction through a Tunneling Process

Trap states in semiconductors usually degrade charge separation and collection in photovoltaics due to trap‐mediated nonradiative recombination. Here, it is found that perovskite can be heavily doped in low concentration with non‐ignorable broadband infrared absorption in thick films and their trap states accumulate electrons through infrared excitation and hot carrier cooling. A hybrid one‐sided abrupt perovskite/TiO2 p‐N heterojunction is demonstrated that enables partial collection of these trap‐filled charges through a tunneling process instead of detrimental recombination. The tunneling is from broadband trap states in the wide depleted p‐type perovskite, across the barrier of the narrow depleted TiO2 region (<5 nm), to the N‐type TiO2 electrode. The trap states inject carriers into TiO2 through tunneling and produce around‐unity peak external quantum efficiency, giving rise to near‐infrared photovoltaics. The near‐infrared response allows photodetecting devices to work in both diode and conductor modes. This work opens a new avenue to explore the near‐infrared application of hybrid perovskites.