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Formation of polaron pairs and time-resolved photogeneration of free charge carriers in π-conjugated polymers

Eugene Frankevichand Research Center for Material Science andHisao IshiiDepartment of Chemistry , Graduate School of Science , Nagoya University , Nagoya 464-8602 , JapanYasushi HamanakaCenter for Integrated Research in Science and Engineering , Nagoya University , Nagoya 464-8602 , JapanTakahiro YokoyamaDepartment of Chemistry , Graduate School of Science , Nagoya University , Nagoya 464-8602 , JapanAkihiko FujiiSergey LiDepartment of Electronic Engineering , Graduate School of Engineering , Osaka University Yamada-Oka , Suita , Osaka 565-0871 , Japan andKatsumi YoshinoDepartment of Electronic Engineering , Graduate School of Engineering , Osaka University Yamada-Oka , Suita , Osaka 565-0871 , JapanArao NakamuraNagoya UniversityKazuhiko SekiDepartment of Chemistry , Graduate School of Science , Nagoya University , Nagoya 464-8602 , Japan

2000en

ABI

Annotatsiya

We have performed in the present work time-resolved experiments on poly(3-dodecyl-thiophene) (P3DDT) and poly(2,5-dioctyloxy-p-phenylene vinylene) (OO-PPV) films by directly probing the formation of charge carriers responsible for the cw photoconductivity within the time domain of -10 ps to 1 ns. Laser light pulses of 400 nm wavelength, 150 fs width, induced photoconductivity in a sample with a frequency 1 kHz. Red 800 nm light pulses delayed in respect to blue ones were revealed to affect the photoconductivity. The effect of the second pulses increased with the delay time. Red light induced changes of the photoconductivity were positive in OO-PPV, and negative in P3DDT. These results are rationalized as an evidence of delayed not immediate formation of free charge carriers. The carriers seem to be formed within 10 ps after the pumping pulse. A mechanism of formation of free polarons from polaron pair is suggested, which has permitted to explain main feature of the results including different signs of the effect of the red light in different polymers.

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