Proceedings of nanoGe Fall Meeting 2021 (NFM21)
DOI: https://doi.org/10.29363/nanoge.nfm.2021.162
Publication date: 23rd September 2021
Narrow bandgap Pb-Sn-based perovskite photodiodes offer the possibility of spectral sensitivity from the visible to the near infrared but often suffer from relatively high dark current densities under a reverse bias where they are generally operated. Among the common strategies to reduce dark current density, the inclusion of charge-blocking layers between the electrodes and the perovskite layer has become popular. While these blocking layers are successful in increasing the energy barrier for charge injection, the lower limits of dark current density reached experimentally remain typically orders of magnitude higher than the expected intrinsic bulk thermal-generated dark current density. Hence, another process than bulk thermal generation is responsible for the remaining dark current. To find its origin we carefully analyzed the activation energy of the dark current by studying its temperature dependence in optimized Pb-Sn perovskite photodiodes with different bandgaps, employing a series of electron-blocking layers. The results demonstrate that the dark current activation energy corresponds to the energy offset between the highest occupied molecular orbital of the electron blocking layer and the conduction band minimum of the perovskite. As a conseqeunce, thermal charge generation at that interface is the main cause for the dark current and it is governed by the interfacial energy offset at the that interface. By increasing this energy offset by using an appropriate blocking layer, a perovskite photodiode was fabricated that has a wavelength sensitivity up to 1050 nm, combined with an ultralow dark current density of 5 × 10−8 mA cm−2 and noise current of 2 × 10−14 A Hz−1/2.
We acknowledge funding from the Ministry of Education, Culture, and Science (Gravity program 024.001.035) and from Netherlands Organisation for Scientific Research (NWO Spinoza grant).
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