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1,8-diiodooctane acts as a photo-acid in organic solar cells

Doumon, N. Y., Wang, G., Qiu, X., Minnaard, A., Chiechi, R. & Koster, L., 13-Mar-2019, In : Scientific Reports. 9, 14 p., 4350.

Research output: Contribution to journalArticleAcademicpeer-review

The last decade saw myriad new donor polymers, among which benzodithiophene-co-thienothiophene polymers are attractive due to their relatively high power conversion efficiency in bulk heterojunction solar cells. We examine the effect of UV-light on the stability of these polymers. The relationship between the polymer chemical structure and the UV-stability of the cells is explored on the one hand, and on the other hand, the effect of additives on their UV-stability: 1,8-diiodooctane against 1-chloronaphthalene in the cells and 1,8-octanedithiol in solution. For example, PBDTTT-E with 18% efficiency loss is more stable than PBDTTT-ET with 36% loss throughout the exposure. While 1,8-diiodooctane acts as photo-acid and leads to accelerated degradation of the solar cells, 1-chloronaphthalene does not. Acidity is known to be detrimental to the efficiency and stability of organic solar cells. The degradation is initiated upon UV-irradiation by the cleavage of the side chains, resulting in more electron traps and by the formation of iodine, dissolved HI and carbon-centered radicals from 1,8-diiodooctane as revealed by 1H NMR spectrum. The 1,8-octanedithiol spectra do not show such species. Finally, the mechanisms behind the effect of 1,8-diiodooctane are explained, paving the way for the design of new, efficient as well as stable materials and additives.
Original languageEnglish
Article number4350
Number of pages14
JournalScientific Reports
Volume9
Publication statusPublished - 13-Mar-2019

    Keywords

  • optoelectronic devices, Organic photovoltaics, Photodegradation, photo-acid, diiodooctane, CONJUGATED POLYMERS, EFFICIENCY, PERFORMANCE, MORPHOLOGY, STABILITY, ADDITIVES, PHOTOSTABILITY, DEGRADATION, FULLERENES, ACCEPTOR

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