Electron Transport Layer Optimization for All-Inorganic, Vacuum-Deposited Perovskite-Based Photodiodes with Improved Reverse Bias Stability and High Speed

Having proven their potential as visible and near-infrared light detectors, metal halide perovskites are now being integrated with thin-film transistor- or silicon-based read-out circuits for high-resolution imaging applications. Vacuum-deposited, all-inorganic perovskite photodiodes (PePDs) offer a superior alternative to solution-processed hybrid organic–inorganic perovskites, addressing their specific limitations in semiconductor fabrication process compatibility. Specifically, vacuum processing overcomes challenges related to limited scalability and reproducibility, while the development of photodiodes made entirely of inorganic compounds improves their resilience at high-temperature environments. At the same time, the performance of vacuum-deposited, all-inorganic PePDs has proven competitive with that of their solution-processed hybrid organic–inorganic counterparts. Building on this progress, this study demonstrates that the careful tuning of the electron transport layer (ETL) can achieve a 3-fold optimization in the performance of all-inorganic, vacuum-deposited PePDs, through improvements in device performance repeatability, operational stability under reverse bias, and carrier extraction speed. Specifically, we identify that the combination of a fullerene and a metal oxide transport layer, as well as the careful tuning of their respective thicknesses, can simultaneously prevent metallic shorts, reduce the amount of interface defect states, and extend the depletion width of the photodiode. Eventually, the optimized photodiodes exhibit minimal variability in device performance, maintaining a stable dark current density below 0.1 μA/cm 2 even after biasing at −2 V for 1 h. They also demonstrate a rise time below 2 μs, with results confirming the potential for sub-μs response times for further scaled-down pixel sizes.