ZnO-Based Photomultiplication-Type Infrared Photodetectors for Ultrasensitive Upconverters

High-sensitivity infrared photodetectors have attracted attention due to their broad applications. Photomultiplication is an ideal choice for high-sensitivity photodetectors since it can generate large photogenerated current under incident faint illumination, making them more user-friendly and cost-effective without any extra amplifier circuits. In this work, 2 wt.% acetic acid in methanol is optimized to treat the electron-accumulated ZnO layer in photodetector ITO/ZnO/PbS/Ag by increasing its interfacial oxygen vacancies, thus the interfacial band bends at the ZnO/PbS interface due to the accumulated charges under illumination. In this way, a high-gain photomultiplication-type photodetector ITO/ZnO/PbS/Ag, in which PbS colloidal quantum dots (CQDs) act as the active layer, is presented. As a result, a high responsivity of 524 A/W with a high external quantum efficiency of 66516% is achieved from the photodetector ITO/ZnO/PbS/Ag under 0.2 µW cm⁻² 980 nm illumination at -1 V. Further, a low turn-on voltage of 2 V is obtained from the upconverters ITO/ZnO/PbS(240 nm)/TAPC(50 nm)/CBP:Ir(ppy)₃(60 nm)/BCP(20 nm)/LiF(1nm)/Al under 1.637 mW cm⁻² 980 nm illumination, exhibiting a photon-to-photon conversion efficiency of 11.08%. In addition, upconversion imaging through a single-pixel device and a 16 × 16 display array is demonstrated, implying its potential scalable applications. Therefore, it provides a promising and applicable pathway for high-performance upconverters.