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Dresden 2009 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 44: Organic semiconductors I

HL 44.7: Talk

Thursday, March 26, 2009, 12:30–12:45, POT 51

Oxygen-Influence on P3HT studied by Photoluminescence and Electron Spin Resonance — •Andreas Sperlich1, Hannes Kraus1, Carsten Deibel1, and Vladimir Dyakonov1,21Experimental Physics VI, Physical Institute, Julius-Maximilians-University of Würzburg, Am Hubland, D-97074 Würzburg — 2ZAE Bayern, Div. Functional Materials for Energy Technology, Am Hubland, D-97074 Würzburg

The influence of oxygen on polymers is crucial to understand and prevent aging effects of organic polymer:fullerene solar cells. We simultaneously performed photoluminescence (PL) and light-induced electron spin resonance (L)ESR studies of the influence of oxygen on thin films of poly(3-hexylthiophene) (P3HT). The samples were illuminated by a 532nm green laser at 100K. In vacuum, P3HT shows a strong PL, as the optically excited singlet excitons (spin=0) recombine completely radiatively, whereas no ESR-signal is observed. When introducing oxygen, the PL is quenched within seconds and a growing ESR-signal from polarons on the P3HT can be observed. This is due to oxygen absorbing an electron by the polymer, leaving an ESR-active hole behind. The influence of oxygen on the polymer is slow in dark and very rapid under illumination. When turning off the illumination, the ESR-signal remains almost constant, which indicates that the signal is corresponding to deep traps. The process is mostly reversible by applying vacuum and 140C for several minutes. We discuss our findings with respect to the application in organic solar cells.

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