Photoelectron spectroscopy of new hole conductors for dye-sensitized solar cells

Bertrand Philippe^a, Stefan Book^a, Rebecka Lindblad^a, Håkan Rensmo^a, Ute Cappel^a

^aUppsala University, Sweden, Uppsala, Sweden

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Ute Cappel, 268
Publication date: 5th February 2015

Small molecular hole conductors have played an important part in OLEDs as well as in solid state dye-sensitized and organic solar cells. 2,2'7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (spiro-OMeTAD) has remained the best performing hole conductor for dye-sensitized solar cells since its initial application in 1998. Especially, since the recent emergence of organic-inorganic perovskite solar cells, there is a large interest in the development of new and cheaper hole conductors which can outperform spiro-OMeTAD. Recently, some simple molecular hole conductors (called X3 and MeO-TPD) were developed which showed great potential in combination with organic dyes in dye-sensitized solar cells [1,2]. For these hole conductors as well as for spiro-MeOTAD the use of chemical doping is required for efficient solar cell operation. We have used X-ray photoelectron spectroscopy (XPS) to learn more about the properties of these new hole conductors in comparison to spiro-MeOTAD. XPS allows for the determination of the energy levels of the hole conductors in relation to the TiO₂ substrate. Furthermore, the effect of doping on the Fermi level can be determined [3]. In this presentation, we will show the energy alignment of the different hole conductors and the effect of doping using LiTFSI or Co complexes. Our findings can be used to draw conclusions for the future development of hole conductors for solar cell applications.

[1] B. Xu, H. Tian, D. Bi, E. Gabrielsson, E. M. J. Johansson, G. Boschloo, A. Hagfeldt, L. Sun, J. Mater. Chem. A 1, 14467-14470 (2013) [2] L. Yang, B. Xu, D. Bi, H. Tian, G. Boschloo, L. Sun, A. Hagfeldt, E. M. J. Johansson J. Am. Chem. Soc. 135, 7378-7385 (2013) [3] R. Schölin, M. H. Karlsson, S. K. Eriksson, H. Siegbahn, E. M. J Johansson, H. Rensmo, J. Phys. Chem. C 116, 26300-26305 (2012)

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