In situ study of a single crystal model system for inverted perovskite solar cells
Karen Radetzky a, Alberto Garcia Fernandez b, Birgit Kammlander a, Evelyn Johannesson a, Rahul Varma a, Håkan Rensmo a, Ute Cappel a
a Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
b Division of Applied Physical Chemistry, Department of Chemistry, KTH - Royal Institute of Technology.
Poster, Karen Radetzky, 172
Publication date: 6th February 2024

Lead halide perovskite solar cells are becoming increasingly competitive with commercial silicon-based devices regarding their performance, reaching over 25 % efficiency in recent years. Since perovskite thin film solar cells are based on a stacked layer design, understanding the interfaces of the employed absorber and selective contacting materials in terms of charge generation, charge separation, and energy alignment is key to advance device development and to address remaining stability issues. Herein, single crystals can serve as model systems to study the fundamental properties of perovskites.

Methylammonium lead iodide (MAPI) and cesium formamidinium lead iodide (CsFAPI) are common absorber materials in perovskite solar cells. The combination of the respective perovskite single crystal with a fullerene (C60) electron transporting layer, a bathocuproine (BCP) passivation layer, and silver contacts then represents the back half of a thin film solar cell device with inverted architecture from charge generation to electron extraction. We sequentially assembled these stacked layers via in situ thermal evaporation and studied them by photoelectron spectroscopy. Thereby, the individual materials, interfaces, and degradation were investigated. Herein, differences between the perovskite compositions and how these translate to the electronic structure of the entire device are of major interest. In this poster, I will show how the results from our photoelectron spectroscopy study are used to construct a band alignment diagram visualizing the interface energetics of the solar cell. Within this description, we compare MAPI and CsFAPI based half cells.

This work was partially supported by the Wallenberg Initiative Materials Science for Sustainability (WISE) funded by the Knut and Alice Wallenberg Foundation. Research at the FlexPESbeamline at MAX IV in Lund, Sweden was conducted under Proposal 20230156. The authors kindly thank Alexei Preobrajenski, Stephan Appelfeller, and Alexander Generalov for their assistance and support during the beamtime.

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