High-Performance CsPbBr₃ Quantum Dot/ZTO Heterojunction Phototransistor with Enhanced Stability and Responsivity

Although all inorganic metal halide perovskite quantum dots (QDs) have shown great potential in photodetectors, many reported devices still suffer from low responsivity due to poor mobility and high defect densities. To overcome these challenges, heterojunction structures that separate electron and hole pathways have emerged as a promising approach to improve the responsivity by reducing radiative recombination. Two-dimensional materials such as graphene and MoS₂ have been integrated with perovskites to enhance performance; however, these materials often lead to high dark-state currents, which hinder the on/off ratios in photodetectors. Hence, identifying alternative functional materials that can complement perovskite QDs while minimizing these drawbacks is critical. Amorphous metal oxide semiconductors, such as zinc tin oxide (ZTO), have attracted attention as high-performance channel materials in thin-film transistors (TFTs) due to their high field-effect mobility, thermal stability, and ability to be processed at low temperatures over large areas. However, ZTO suffers from persistent photoconductivity (PPC) caused by oxygen vacancies, which leads to slow response times and prolonged conductivity after light exposure, thereby limiting its effectiveness in optoelectronic devices. In this work, we demonstrate a high-performance phototransistor using a planar heterojunction structure composed of CsPbBr₃ quantum dots and ZTO via a simple solution-processing method. This device exhibits a responsivity of over 10³ A/W, a specific detectivity of 7.0 × 10¹⁴ Jones, and an on/off ratio of 5 × 10⁴ under 390 nm light illumination with an intensity of 0.03 mW/cm². The combination of ZTO and CsPbBr₃ QDs offers significant improvements over devices that lack either layer, showcasing superior performance compared to that of most perovskite photodetectors.