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The difference in electronic structure of MAPI and MASI perovskites and its effect on the interface alignment to the HTMs spiro-MeOTAD and CuI

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Abstract

We have studied the electronic structure of CH3NH3PbI3 (MAPI) and CH3NH3SnI3 (MASI) perovskite films by performing X-ray photoelectron spectroscopy (XPS) measurements on in situ grown perovskite films. For the MASI perovskite we observed a 0.7 eV lower ionization potential (IP) as compared to MAPI. Thus, the band edges of MASI are positioned energetically higher with respect to MAPI. In addition, we found MASI to form p-type and MAPI n-type doping. To investigate the impact of different electronic structures on the line up to hole transport materials (HTMs) we performed detailed interface experiments using two commonly used HTMs: spiro-MeOTAD and CuI. The HTMs were step-by-step deposited onto in situ prepared MAPI and MASI layers and characterized via XPS and ultraviolet photoelectron spectroscopy (UPS) after each deposition step. Our results show that the lower IP of MASI results in blocking barriers at the spiro-MeOTAD interface as well as at the CuI contact. We also propose an estimated band alignment of the two perovskites to the TiO2 front contact by using the vacuum level as the reference energy. The higher lying conduction band maximum (CBM) of MASI as compared to MAPI would limit the open-circuit voltage (VOC) of a solar cell. Furthermore, for a doped spiro-MeOTAD layer, a VOC value of up to 750 mV is expected at the MAPI|doped spiro-MeOTAD interface, while it is limited to 210 mV in the case of MASI. Our results show that MASI specific HTMs and ETMs have to be found in order to improve the efficiency of MASI based solar cells.

Graphical abstract: The difference in electronic structure of MAPI and MASI perovskites and its effect on the interface alignment to the HTMs spiro-MeOTAD and CuI

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Publication details

The article was received on 14 Dec 2018, accepted on 20 Mar 2019 and first published on 26 Mar 2019


Article type: Paper
DOI: 10.1039/C8TC06332J
Citation: J. Mater. Chem. C, 2019, Advance Article

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    The difference in electronic structure of MAPI and MASI perovskites and its effect on the interface alignment to the HTMs spiro-MeOTAD and CuI

    T. Hellmann, M. Wussler, C. Das, R. Dachauer, I. El-Helaly, C. Mortan, T. Mayer and W. Jaegermann, J. Mater. Chem. C, 2019, Advance Article , DOI: 10.1039/C8TC06332J

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