Pyridination of Hole Transporting Materials in Perovskite Solar Cells

Artiom Magomedov^a, Ernestas Kasparavičius^a, Kasparas Rakstys^b, Sanghyun Paek^b, Natalia Gasilova^b, Kristijonas Genevičius^c, Gytis Juška^c, Tadas Malinauskas^a, Mohammad Khaja Nazeeruddin^b, Vytautas Getautis^a

^aDepartment of Organic Chemistry, Kaunas University of Technology, Radvilenu 19, 50254, Kaunas, Lithuania

^bGroup for Molecular Engineering of Functional Materials, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), CH-1951 Sion, Switzerland

^cDepartment of Solid State Electronics, Vilnius University, Saulėtekio 9, Vilnius, 10222, Lithuania

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV18)

Benidorm, Spain, 2018 May 28th - 31st

Organizers: Emilio Palomares and Rene Janssen

Poster, Artiom Magomedov, 111
Publication date: 21st February 2018

In the highest efficiency perovskite solar cells (PSCs) molecules containing methoxydiphenylamine-substituted fluorene^[1,2] and carbazole^[3] derivatives are routinely used as a hole transporting materials (HTMs), with spiro-OMeTAD being the most popular HTM. However, these HTMs in their pristine form generally show low performance due to the low conductivity. Thus several dopants, such as FK209, lithium bis(trifluoromethane)sulfonamide (LiTFSI), and tert-butylpyridine (tBP), are usually added to the HTM solution before layer formation. Unfortunately, use of the dopants typically result in reduced long-term performance, and dopant-free HTM based devices generally have higher stability.

In this work, for the first time, reactive radical-cation species present in HTM layer were shown to react with tBP additive. New pyridinated products were isolated and characterized by means of NMR and MS analysis. In addition, their optical and photophysical properties (i.e., solid-state ionization potentials (I_p), cyclic voltammetry (CV), UV/vis characteristics, and conductivities) were determined. Furthermore, pyridinated products were detected in the aged PSCs by means of mass spectrometry, and shown to have negative influence on the overall device performance. We believe that these findings will help to improve the long-term stability of PSCs by either molecular engineering of HTMs or utilization of less-reactive or sterically hindered pyridine derivatives.

[1] M. Saliba, S. Orlandi, T. Matsui, S. Aghazada, M. Cavazzini, J.-P. Correa-Baena, P. Gao, R. Scopelliti, E. Mosconi, K.-H. Dahmen, et al., Nat. Energy 2016, 1, 15017.

[2] T. Malinauskas, M. Saliba, T. Matsui, M. Daskeviciene, S. Urnikaite, P. Gratia, R. Send, H. Wonneberger, I. Bruder, M. Graetzel, et al., Energy Environ. Sci. 2016, 9, 1681–1686.

[3] P. Gratia, A. Magomedov, T. Malinauskas, M. Daskeviciene, A. Abate, S. Ahmad, M. Grätzel, V. Getautis, M. K. Nazeeruddin, Angew. Chemie Int. Ed. 2015, 54, 11409–11413.

[4] H. Lund, Acta Chem. Scand. 1957, 11, 1323–1330.

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