Improved evaluation of deep-level transient spectroscopy on perovskite\n solar cells reveals ionic defect distribution

Abstract

One of the key challenges for future development of efficient and stable\nmetal halide perovskite solar cells is related to the migration of ions in\nthese materials. Mobile ions have been linked to the observation of hysteresis\nin the current--voltage characteristics, shown to reduce device stability\nagainst degradation and act as recombination centers within the band gap of the\nactive layer. In the literature one finds a broad spread of reported ionic\ndefect parameters (e.g. activation energies) for seemingly similar perovskite\nmaterials, rendering the identification of the nature of these species\ndifficult. In this work, we performed temperature dependent deep-level\ntransient spectroscopy (DLTS) measurements on methylammonium lead iodide\nperovskite solar cells and developed a extended regularization algorithm for\ninverting the Laplace transform. Our results indicate that mobile ions form a\ndistribution of emission rates (i.e. a distribution of diffusion constants) for\neach observed ionic species, which may be responsible for the differences in\nthe previously reported defect parameters. Importantly, different DLTS modes\nsuch as optical and current DLTS yield the same defect distributions. Finally\nthe comparison of our results with conventional boxcar DLTS and impedance\nspectroscopy (IS) verifies our evaluation algorithm.\n