p-Doping in Amide-Based Hole-Transport Materials for Perovskite Solar Cells
Benjamin Vella a, Pablo Docampo a, Graeme Cooke a
a School of Chemistry, University of Glasgow, University Pl, G12 8QQ, Glasgow, UK
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, Benjamin Vella, 273
Publication date: 20th April 2022

The hole-transport layer is an indispensable part of perovskite solar cells, used to extract holes from the photoactive perovskite layer and transport them to the electrode. Small molecule organic semiconductors have low hole conductivities and mobilities in their pristine form, and in order to render them feasible for use in solar cells they inevitably require chemical doping to introduce additional holes into the HTM matrix in order to improve their charge carrier densities and thus their conductivity.[1]

Most research involving these dopants has focused on spiro-OMeTAD, as it has become the standard HTM incorporated into perovskite solar cells. Commonly used dopants such as LiTFSI, ZnTFSI, and FK209 form complexes with spiro-OMeTAD, extracting electrons from the HTM thus injecting additional holes into the matrix. While the mechanisms for doping this HTM have now been well understood,[1–3] there has been little research into how these dopants interact with low-cost alternatives such as amide-based HTMs. In these materials, lithium ions can easily coordinate with the amide carbonyl group, leading to defined changes in the C=O signal in UV-visible and infrared spectroscopy, and this has been observed in one such HTM,
EDOT-Amide-TPA, doped with LiTFSI.[4] This behaviour differs from the usual redox mechanism by which LiTFSI dopes spiro-OMeTAD. To date, the mechanisms by which Zn(TFSI)2 or FK209 interact with amide bonds, and the effects of changing the valency on the metal cation (Li+, Zn2+, Co3+) have not been explored. Increasing the charges on the cations may allow further coordination with more carbonyl groups, leading to chelates or dimers/trimers of separate HTM molecules coordinated to a central metal ion. 

This study will focus on the ionic doping of amide bonds in the context of hole-transport materials for perovskite solar cells. A series of HTMs containing amide functionalities has been synthesised, and the interactions with the aforementioned dopants will be explored. Device measurements with the doped HTMs will be taken and consolidated with UV-visible and IR spectroscopy measurements to determine the doping mechanism.


1. T. H. Schloemer, J. A. Christians, J. M. Luther and A. Sellinger, Chem. Sci., 2019, 10, 1904–1935.

2. Y. Saygili, H. S. Kim, B. Yang, J. Suo, A. B. Muñoz-Garcia, M. Pavone and A. Hagfeldt, ACS Energy Lett., 2020, 5, 1271–1277.

3. S. Wang, W. Yuan and Y. S. Meng, ACS Appl. Mater. Interfaces, 2015, 7, 24791–24798.

4. M. L. Petrus, K. Schutt, M. T. Sirtl, E. M. Hutter, A. C. Closs, J. M. Ball, J. C. Bijleveld, A. Petrozza, T. Bein, T. J. Dingemans, T. J. Savenije, H. Snaith and P. Docampo, Adv. Energy Mater., 2018, 8, 1–11.

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