Removal of Residual Diiodooctane Improves Photostability of High-Performance Organic Solar Cell Polymers

Bertrand Tremolet de Villers, Dana Olson, Nikos Kopidakis, Kathryn O'Hara, Dave Ostrowski, Perry Biddle, Michael Chabinyc, Sean Shaheen

Research output: Contribution to journalArticlepeer-review

237 Scopus Citations


Solvent additives such as diiodooctane (DIO) are becoming ubiquitous in processing high performance organic photovoltaic (OPV) active layers. Here, we investigate the effects of DIO on the long-term stability of the active layer by studying the photodegradation under ambient white light illumination of the polymer PTB7-Th in pure polymer thin films and in blend films with PC71BM. Using X-ray fluorescence, we directly detect iodine in the active layer films, indicating the presence of residual DIO after casting from solution. Additionally, we show that this residual DIO dramatically decreases the photostability of the active layer. Structural changes in the films upon illumination are probed with grazing-incidence wide-angle X-ray scattering (GIWAXS). FTIR spectroscopy is used to monitor chemical changes in the polymer structure during irradiation in the presence of DIO. Furthermore, we demonstrate that film treatment either with high vacuum (10-8 Torr) for 60 min or with a high-temperature thermal anneal at 175 °C for 30 min removes residual DIO from the film and delays photodegradation. Therefore, when processing polymer solar cells with DIO-containing solutions, it is imperative to remove any trace amounts of DIO from deposited films.

Original languageAmerican English
Pages (from-to)876-884
Number of pages9
JournalChemistry of Materials
Issue number3
StatePublished - 9 Feb 2016

Bibliographical note

Publisher Copyright:
© 2016 American Chemical Society.

NREL Publication Number

  • NREL/JA-5900-64579


  • organic photovoltaic
  • polymers
  • stability and degradation


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