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

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