Molecular Packing and Arrangement Govern the Photo-Oxidative Stability of Organic Photovoltaic Materials

William R. Mateker, Thomas Heumueller, Rongrong Cheacharoen, I. T. Sachs-Quintana, Julien Warnan, Xiaofeng Liu, Guillermo C. Bazan, Pierre Beaujuge, Michael D. McGehee

Research output: Contribution to journalArticlepeer-review

66 Scopus citations

Abstract

For long-term performance chemically robust materials are desired for organic solar cells (OSCs). Illuminating neat films of OSC materials in air and tracking the rate of absorption loss, or photobleaching, can quickly screen a material’s photo-chemical stability. In this report, we photobleach neat films of OSC materials including polymers, solution-processed oligomers, solution-processed small molecules, and vacuum-deposited small molecules. Across the materials we test, we observe photobleaching rates that span seven orders of magnitude. Furthermore, we find that the film morphology of any particular material impacts the observed photobleaching rate, and that amorphous films photobleach faster than crystalline ones. In an extreme case, films of amorphous rubrene photobleach at a rate 2500 times faster than polycrystalline films. When we compare density to photobleaching rate, we find that stability increases with density. We also investigate the relationship between backbone planarity and chemical reactivity. The polymer PBDTTPD is more photostable than it’s more twisted and less ordered furan derivitative, PBDFTPD. Finally, we relate our work to what is known about the chemical stability of structural polymers, organic pigments, and organic light emitting diode materials. For the highest chemical stability, planar materials that form dense, crystalline film morphologies should be designed for OSCs.
Original languageEnglish (US)
Pages (from-to)6345-6353
Number of pages9
JournalChemistry of Materials
Volume27
Issue number18
DOIs
StatePublished - Sep 2 2015

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