Probing into Reverse Bias Dark Current in Perovskite Photodiodes: Critical Role of Surface Defects

摘要

Minimizing reverse bias dark current density (J_(dark)) while retaining highexternal quantum efficiency is crucial for promising applications of perovskitephotodiodes, and it remains challenging to elucidate the ultimate originof J_(dark). It is demonstrated in this study that the surface defects inducedby iodine vacancies are the main cause of J_(dark) in perovskite photodiodes.In a targeted way, the surface defects are thoroughly passivated througha simple treatment with butylamine hydroiodide to form ultrathin 2Dperovskite on its 3D bulk. In the passivated perovskite photodiodes, J_(dark) aslow as 3.78 × 10~(-10) A cm~(-2) at -0.1 V is achieved, and the photoresponse isalso enhanced, especially at low light intensities. A combination of the twoimprovements realizes high specific detectivity up to 1.46 × 10~(12) Jones inthe devices. It is clarified that the trap states induced by the surface defectscan not only raise the generation-recombination current density associatedwith the Shockley–Read–Hall mechanisms in the dark (increasing J_(dark)), butalso provide additional carrier recombination paths under light illumination(decreasing photocurrent). The critical role of surface defects on J_(dark) ofperovskite photodiodes suggests that making trap-free perovskite thin films,for example, by fine preparation and/or surface engineering, is a top priorityfor high-performance perovskite photodiodes.