Publication date: 25th September 2020
Mobile ions in metal halide perovskites are causing current-voltage hysteresis in solar cells, and promote degradation and non-radiative recombination. We want to contribute to the understanding of the fundamental properties of ionic transport and its relationship to processing parameters. Therefore, we characterised the ionic defect landscape of methylammonium lead triiodide (MAPbI3) perovskites with fractionally changed precursor stoichiometry [1] by impedance spectroscopy and deep-level transient spectroscopy (DLTS). I will briefly introduce these experimental methods, and how the latter allows to distinguish between electronic traps and ionic defects. With IS, we observed three different ionic defects in MAPbI3 and their migration rates and activation energies. To gain more insight, we applied a newly developed algorithm for performing inverse Laplace transform to evaluate the DLTS capacitance transients. The result reveals a broad distribution of migration rates for each of the observed ionic defect [2]. Our findings show a major impact of the precursor stoichiometry on the defect landscape, with direct consequences for the electronic properties such as the measured built-in potential and the open-circuit voltage. I will also show how we applied the Meyer-Neldel rule to categorise the migration rates of the different ionic defects and discuss where it comes from [3].
[1] P. Fassl, V. Lami, A. Bausch, Z. Wang, M.T. Klug, H.J. Snaith, and Y. Vaynzof, Fractional deviations in precursor stoichiometry dictate the properties, performance and stability of perovskite photovoltaic devices. Energy & Environmental Science 11, 3380 (2018).
[2] S. Reichert, J. Flemming, Q. An, Y. Vaynzof, J.-F. Pietschmann, and C. Deibel, Ionic-Defect Distribution Revealed by Improved Evaluation of Deep-Level Transient Spectroscopy on Perovskite Solar Cells. Phys. Rev. Applied 13, 034018 (2020).
[3] S. Reichert, Q. An, Y.-W. Woo, A. Walsh, Y. Vaynzof, and C. Deibel, Probing the ionic defect landscape in halide perovskite solar cells. arXiv 2005.06942v1 (2020).
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