Quantum Efficiency Gain in 2D Perovskite Photo and X-Ray Detectors

The perovskite polycrystalline thin film detector fabricated by solution method is a promising low-cost, scalable technology for radiation imaging, but its thin volume limits the sensing efficiency for high-energy X-ray photons. This work reports 2D perovskite thin film photo-diodes with a detection gain when sensing visible and X-ray photons. Detailed power and temperature-dependent device characterizations reveal a charge multiplication effect to be responsible for the observed high gain. This is caused by a disparity in electron and hole transport, where electron transport is retarded by a trap/de-trap process via shallow trap states, whereas the hole transport is fast enough to produce a photoconductive gain in satisfying the charge neutrality. The 2D perovskite made with butylamine spacers is also found to exhibit a larger efficiency gain than those made with phenylethylamines because of the higher likelihood of forming shallow traps in the former. The thin film diodes feature a high temporal response over 1 MHz due to the fast charge collection across a thin volume, and the discovery provides device physics mechanisms in connection to material structure-function relationship for future optoelectronics design that can boost the efficiency of X-ray sensing and dim light detection.