Kavan Ladislav

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University of Szeged

Engineering of Semiconductor Interfaces in Perovskite Photovoltaics Ladislav Kavan  J. Heyrovsky Institute of Physical Chemistry, Dolejskova 3, CZ-18223 Prague 8, Czech Republic E-mail: kavan@jh-inst.cas.cz  Perovskite solar cell (PSC) is called ‘young sister’ of the dye-sensitized solar cell [1]. The key component of the negative electrode (photoanode) is a compact thin film of oxide semiconductor (TiO2 or SnO2). It transport electrons from the photoexcited perovskite (or sensitizing dye) to the collecting terminal (FTO) and prevents recombination of these electrons with a hole-transport medium and/or the photoabsorber. The film should be pinhole-free, allowing fast electron injection and transport, and its conduction band minimum (CBM) must be properly aligned with the CBM of perovskite [2] or LUMO of the dye. Amorphous ALD-made SnO2 or TiO2 films block holes for thicknesses down to several nm, but amorphous and crystalline SnO2 films differ in their CBM positions. They are usually measured by photoelectron spectra (XPS, UPS). An electrochemical alternative is the determination of the flatband potential. Electrochemical studies of single crystal TiO2 (anatase, rutile, brookite) together with vacuum/near-ambient pressure XPS studies and theoretical (DFT) modelling point at the effect of interface, influencing the CBM positions [3]. This knowledge provides relevant inputs not only for PSC development, but also for solar-driven water splitting [4]. Even 1-2 monolayers of water cause significant CBM shifts. TiO2 rutile thin films and or rutile/anatase double-layers turned out to be useful for PSC, too, outperforming even the anatase layers. They can be most simply prepared by thermal oxidation of Ti at FTO [5]. The hole-collecting terminal (e.g. Au) is interfaced to hole-transporting medium. A promising hole-conductor to replace spiro-OMeTAD is CuSCN, particularly if it is separated from Au by a film of reduced graphene oxide (rGO). The natural p-doping of CuSCN is demonstrated by both Hall-effect and by Mott-Schottky plots [6]. Along with small improvement of the performance metrics (efficieny, fill factor, open-circuit votlage) the long term stability of CuSCN/rGO/Au is the main benefit of this PSC architecture. Acknowledgement: This work was supported by the Czech National Science Foundation (contract No. 18-08959S).     [1] Kavan, L., Curr. Opinion Electrochem, 2 (2017) 88-96. [2] Kavan, L., Curr. Opinion Electrochem, 11 (2018) 122-129. [3] Mansfeldova, V., Zlamalova, M., Tarabkova, H., Janda, P., Vorokhta, M., Piliai, L., Kavan, L., J. Phys. Chem. C, 125 (2021) 1902-1912. [4] Nebel, R., Macounova, K.M., Tarabkova, H., Kavan, L., Krtil, P., J. Phys. Chem. C, 123 (2019) 10857-10867. [5] Krysova, H., Zlamalova, M., Tarabkova, H., Jirkovsky, J., Frank, O., Kohout, M., Kavan, L., Electrochim. Acta, 321 (2019) 134685. [6] Kavan, L., Vlckova-Zivcova, Z., Hubik, P., Arora, N., Dar, M.I., Zakeeruddin, S.M., Grätzel, M., ACS Appl. Energy Mater, 2 (2019) 4264-4273.  67

Engineering of semiconductor interfaces in perovskite photovoltaics

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Engineering of semiconductor interfaces in perovskite photovoltaics

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