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Proceedings Paper

Exciton dynamics and device performance in polythiophene heterojunctions for photovoltaics
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Paper Abstract

We present time-resolved photoluminescence studies in conjunction with device characterization of a variety of heterojunctions with poly-(3-hexylthiophene), or P3HT, as a means to understand how exciton dynamics affect device performance. We find that blends of P3HT with the electron-transporting polymer CN-ether-PPV and with the fullerene derivative PCBM result in ~4-fold and ~15-fold improvements in short-circuit currents, respectively, over neat-film P3HT on TiO2 solgel. Despite efficient charge-transfer in P3HT:PCBM films, as evidenced by enhanced device performance and quenched steady-state luminescence, we observe only moderate reduction of the excited state lifetime, due to the already efficient non-radiative pathways in P3HT. We observe evidence for a new state that we assign to an exciplex in blends of P3HT with the electron-transporting polymer CN-ether-PPV. The exciplex state, which confirms the existence of charge-transfer between the two polymers, may account for the enhanced device performance of these blends by acting as a scavenger for excitons that would otherwise decay rapidly via non-radiative pathways. The long-range order of P3HT is disrupted when spin-cast on rough TiO2 nanoparticles, and this results in a blueshift of the PL spectrum and a new long-lived decay component that we attribute to long-lived intrachain polarons. P3HT on smooth TiO2 solgel films shows little or no quenching of the excited state, despite known charge transfer from P3HT to TiO2.

Paper Details

Date Published: 3 October 2005
PDF: 11 pages
Proc. SPIE 5938, Organic Photovoltaics VI, 59380J (3 October 2005); doi: 10.1117/12.614243
Show Author Affiliations
Stephanie V. Chasteen, Univ. of California, Santa Cruz (United States)
Sue A. Carter, Univ. of California, Santa Cruz (United States)
Garry Rumbles, National Renewable Energy Lab. (United States)

Published in SPIE Proceedings Vol. 5938:
Organic Photovoltaics VI
Zakya H. Kafafi; Paul A. Lane, Editor(s)

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