Characterization of lead halide perovskite solar cells and materials by Electron Paramagnetic Resonance Spectroscopy
Shipra Prakash a, Byeong Jo Kim b, Anuja Vijayan b, Malin Johansson b, Gerrit Boschloo b, Fikret Mamedov a
a Molecular Biomimetics, Department of Chemistry – Ångström Laboratory, Uppsala University, 75120 Uppsala, Sweden
b Physical Chemistry, Department of Chemistry – Ångström Laboratory, 752 36 Uppsala, Suecia, Sweden
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Poster, Shipra Prakash, 280
Publication date: 20th April 2022

Lead halide perovskites, solar cell materials with drastically improved solar conversion efficiency are emerging as a feasible alternative for traditional solar cells in the recent decade. However, lead halide perovskites are unstable and degrade when exposed to moisture, high temperatures, oxygen and UV light. In addition, impurities and defects centers produced during fabrication can also reduce the conversion efficiency in these materials. It is therefore essential to characterize impurities, formation of defect centers, degradation pathways and degradation products. Knowledge about the genesis and structure of defect states and degradation mechanisms can optimize and further improve the efficiency and stability of the solar cells. Defect states n perovskitebased solar cells are often paramagnetic through electrically-, optically-, or structurally-induced processes, e.g. charge separation or photo-induced charge transfer. Electron Paramagnetic Resonance (EPR) spectroscopy is thus the method of choice to investigate the electronic structure and location of defect sates in perovskite solar cells. In the present work, EPR spectroscopy has been performed on MAPbI3 based solar cell materials. A series of MAPbI3 thin films on a polymer (PEN/ITO) substrate were prepared. The build-up and decay of the light induced EPR signal in these films was measured over a few hours. EPR signals were also measured in MAPbI3 films that were made with and without spiro-OMeTAD as the hole transport material. EPR signals have been assigned to the holes (SPIRO•+, Pb3+) formed in the films and the amount of hole carriers were estimated in all the samples. A comparison of EPR measurements on MAPbI3 crystals to MAPbI3 thin films is also presented. The results show that EPR spectroscopy is a powerful tool in characterizing perovskite solar cells at the electronic level.

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