Explaining the drop in open-circuit voltage of co-evaporated FACsPbIBrCl perovskites with increased chloride content using drift-diffusion simulations
Sander Heester a, Federico Ventosinos b, Lidón Gil-Escrig b, Henk Bolink b, Jan Anton Koster a
a Zernike Institute for Advanced Materials, University of Groningen, The Netherlands, Nijenborgh, 7, Groningen, Netherlands
b Instituto de Ciencia Molecular, Universidad de Valencia, Paterna, Valencia, 46980, Spain, Carrer del Catedrátic José Beltrán Martinez, 2, Paterna, Spain
Oral, Sander Heester, presentation 078
Publication date: 6th February 2024

Co-evaporation is an established technique for deposition of thin films and a promising method to create solvent-free perovskite solar cells with high performance. Among these perovskites is FACsPbIBrCl, which is a type of perovskite that is well suited for wide band gap applications such as tandem cells. To further increase their performance, we want to increase the open circuit voltage of these subcells. This is, among other things, affected by the halide composition of the perovskite. In our co-evaporated FACsPbIBrCl perovskite solar cell with organic transport layers, we tried to achieve this by varying the chloride content. However, adding an increasing amount of chloride to the perovskite results in a substantial drop in open-circuit voltage up to 0.2V. Here we show that the drop in open circuit voltage can only be explained by an increased step in band energies between the different layers in the device. We demonstrate this via a comprehensive and thorough JV curve fitting strategy using the drift-diffusion simulation software SIMsalabim[1]. We found that the introduction of an energy step between the valence bands of the perovskite and the electron transport layer is the only scenario that can explain the drop in open-circuit voltage. The energy step must be at least 0.3 eV. Our results provide an explanation for the decrease in performance when increasing the chloride content of the co-evaporated FACsPbIBrCl, in contrast to our initial expectations. We anticipate that, as we have shown numerically, that with an energetic re-optimization of the electron transport layer, the drop in open-circuit voltage can be avoided.

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