Tuning Perovskite Composition for Low Dark Current and High Specific Detectivity Photodetectors

Organo-metal halide perovskites have gained attention for their remarkable optoelectronic properties, which made them an ideal material for photodetectors (PDs). In particular, modern PDs require to be cost-effective, self-powered, highly sensitive and flexible, all conditions that can be fulfilled by using a perovskite-based active layer.<br/>The route to obtain highly sensitive sensors requires minimizing dark current (J_d) values, which limits the noise (i_n) in devices and maximizes light conversion. To date, few methods exist to reduce the dark current in perovskite PDs. They are based on the use of charge-blocking layers to minimize charge injection¹. Other strategies are related to inclusion of additives or controlling film crystallization² to minimize backward charge injection at the electrodes. However, there is a deficit of efforts focused on understanding the role of perovskite composition and its correlation to device J_d.<br/>In recent years, compositional engineering has played a fundamental role in developing perovskite solar cells, enabling higher device efficiencies, an adjustment of film defect densities and longer stabilities³. In this work⁴, we study the effect of tuning the perovskite composition and report the performance of PDs fabricated with these active layers. We obtained ultra-low J_d values of 1.3 x 10^-9 A cm^-2 at –0.5 V with specific detectivity approaching 10¹³ Jones. Moreover, we observe for the first time a linear relationship between the J_d of devices and their V_oc over the 0-15 % Br range.<br/>With a combination of optoelectronic measurements, transient analyses, impedance spectroscopy and morphological investigations, we attributed the low J_d of the of the 15% Br containing devices to the reduction of trap states, a better charge extraction of photogenerated carriers and an improvement in photoactive layer morphology and crystallinity.<br/>Therefore, we demonstrate how compositional engineering of the active layer can be an alternative approach to conventional transport layer optimization to improve photodetector performances.<br/><br/>References<br/><br/>1 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 and G. H. Gelinck, <i>Nat. Commun.</i>, 2021, <b>12</b>, 7277.<br/>2 T. Du, F. Richheimer, K. Frohna, N. Gasparini, L. Mohan, G. Min, W. Xu, T. J. Macdonald, H. Yuan, S. R. Ratnasingham, S. Haque, F. A. Castro, J. R. Durrant, S. D. Stranks, S. Wood, M. A. McLachlan and J. Briscoe, <i>Nano Lett.</i>, 2022, <b>22</b>, 979–988.<br/>3 M. Saliba, S. Orlandi, T. Matsui, S. Aghazada, M. Cavazzini, J.-P. Correa-Baena, P. Gao, R. Scopelliti, E. Mosconi, K.-H. Dahmen, F. De Angelis, A. Abate, A. Hagfeldt, G. Pozzi, M. Graetzel and M. K. Nazeeruddin, <i>Nat. Energy</i>, 2016, <b>1</b>, 15017.<br/>4 F. Furlan, D. Nodari, E. Palladino, E. Angela, L. Mohan, J. Briscoe, M. J. Fuchter, T. J. Macdonald, G. Grancini, M. A. McLachlan and N. Gasparini, <i>Adv. Opt. Mater.</i>, 2022, 2201816.