Mechanism of carrier photoexcitation in semiconducting polymers: the role of electron photoemission in photoconductivity measurements

Daniel Moses; Paulo B. Miranda; Cesare Soci; Alan J. Heeger

doi:10.1117/12.456939

21 February 2002 Mechanism of carrier photoexcitation in semiconducting polymers: the role of electron photoemission in photoconductivity measurements

Daniel Moses, Paulo B. Miranda, Cesare Soci, Alan J. Heeger

Author Affiliations +

Proceedings Volume 4465, Organic Photovoltaics II; (2002) https://doi.org/10.1117/12.456939
Event: International Symposium on Optical Science and Technology, 2001, San Diego, CA, United States

Abstract

Ultrafast photoinduced absorption by infrared-active vibrational modes (IRAV) is used to detect charged photo- excitations (polarons) in solid films of conjugated luminescent polymers. Experiments, carried out in zero applied electric field, show that polarons are generated within 100 fs with quantum efficiencies of approximately 10%. The ultrafast photoinduced IRAV Absorption, the weak pump-wavelength dependence, and the linear dependence of charge density on pump intensity indicate that both charged polarons and neutral excitons are independently generated even at the earliest times. Measurements of the excitation profile of the transient and steady-state photoconductivity of poly(phenylene vinylene) and its soluble derivatives over a wide spectral range up to h(upsilon) = 6.2 eV indicate an apparent increase in the photoconductivity at h(upsilon) > 3- 4 eV that arises from external currents generated by electron photoemission (PE). After quenching the PE by addition of CO₂+SF₆ (90%:10%) into the sample chamber, the bulk photoconductivity is nearly independent of photon energy in all polymers studied, in a good agreement with the IRAV spectra. The single threshold for photoconductivity is spectrally close to the onset of (pi) - (pi) ^* absorption, behavior that is inconsistent with a large exciton binding energy.

Citation Download Citation

Daniel Moses, Paulo B. Miranda, Cesare Soci, and Alan J. Heeger "Mechanism of carrier photoexcitation in semiconducting polymers: the role of electron photoemission in photoconductivity measurements", Proc. SPIE 4465, Organic Photovoltaics II, (21 February 2002); https://doi.org/10.1117/12.456939

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