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 Dyakonov^1,2 — ¹Experimental 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 140^∘C for several minutes. We discuss our findings with respect to the application in organic solar cells.