Understanding and Reducing Dark Currents in Perovskite Photodetectors

Perovskite semiconductors offer the possibility of spectral sensitivity from the visible to the near infrared and can be used in future photodetection applications like image sensing,^[1] optical communication, environmental and health monitoring, or chemical and biological detection. Perovskite photodiodes, however, often suffer from relatively high dark current densities under reverse bias. 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. By determining the activation energy of the dark current in optimized perovskite photodiodes with different bandgaps and employing a series of electron-blocking layers, we find that the 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.^[2] 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.^[2]<br/>To further increase performance we employ low-dimensional perovskites. Perovskite thin films with a vertical gradient in dimensionality result in graded electronic bandgap structures that are ideal for photodiode applications. Positioning low-dimensional, vertically-oriented perovskite phases at the interface with the electron blocking layer further increases the activation energy for thermal charge generation and thereby effectively lowers the dark current density to a record-low value of 5 × 10⁻⁹mA cm⁻² without compromising responsivity, resulting in a noise-current-based specific detectivity exceeding 7 × 10¹² Jones at 600 nm.^[3] These multidimensional perovskite photodiodes show promising air stability and a dynamic range over ten orders of magnitude, and thus represent a new generation of high-performance low-cost photodiodes.^[3]<br/><b>References</b><br/>[1] A. J. J. M. van Breemen, R. Ollearo, S. Shanmugam, B. Peeters, L. C. J. M. Peters, R. van de Ketterij, H. B. Akkerman, C. H. Frijters, F. Di Giacomo, S. Veenstra, R. Andriessen, R. A. J. Janssen, E. Meulenkamp, and G. H. Gelinck<b>, </b><i>Nat. Electron.</i> <b>4</b>, 818 (2021).<br/>[2[ R. Ollearo, J. Wang, M. J. Dyson, C. H. L. Weijtens, M. Fattori, B. T. van Gorkom, A. J. J. M. van Breemen, S. C. J. Meskers, R. A. J. Janssen, G. H. Gelinck, <i>Nat. Commun</i>. <b>12</b>, 7277 (2021).<br/>[3] R. Ollearo, A. Caiazzo, J. Li, M. Fattori, A. J. J. M. van Breemen, M. M. Wienk, G. H. Gelinck, and R. A. J. Janssen, <i>Adv. Mater.</i><b> 34</b>, 2022, 202205261 (2022).