Ambipolar Photoresponse of CsPbX₃-ZnO (X = Cl, Br, and I) Heterojunctions

All-inorganic perovskite CsPbX3 (X = Cl, Br, and I) quantum dots (QDs) are emerging as attractive materials for photodetectors due to their prominent positive photoresponse. In this work, ambipolar photodetectors were constructed based on heterojunctions of CsPbX3 QDs and ZnO nanocrystals (NCs). The transition between the positive photoconductivity (PPC) and negative photoconductivity (NPC) was successfully controlled not only by the drain-source voltage (VDS) but also by the excitation wavelength and CsPbX3 crystal size. A high responsivity (R), on–off ratio (η), and detectivity (D*) were achieved for NPC (R = 1046 mA/W, η = 281, and D* = 1.65 × 1011 Jones), with PPC (R = 146 mA/W, η = 64, and D* = 1.54 × 1011 Jones) simultaneously revealed in the same device. A general mechanism combining the type-II heterojunction, the component and size-related band structure, and most critically the in-band trap states of the perovskites was established for understanding the unique ambipolar property. It exhibits application potential in developing functional photodetectors, memristors, and optical logic devices.