We characterize and compare blended and bilayered heterojunctions of polymer photovoltaic devices using poly[oxa-1,4-phenylene-1,2-(1-cyano)-ethenylene-2,5-dioctyloxy-1,4-phenylene-1,2-(2-cyano)-ethenylene-1,4-phenylene] (CN-ether-PPV) and poly[2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-1,2-ethenylene] (M3EH-PPV) as electron- and hole-transporting polymers, respectively. We find that both blended and bilayered structures have substantially improved current densities and power efficiencies ( under white light) over neat films. Improved exciton dissociation at multiple interfaces and reduced recombination due to energy and charge transfers increases the charge-carrier collection in both types of heterojunction devices, but low electron mobilities in the polymers lead to low fill factors and reduced quantum efficiency that limit the power efficiency. Time-resolved photoluminescence reveals that for blended structures both the hole and electron-transporting polymers undergo efficient quenching with the exciton decay being dominated by the existence of two fast decay channels of 0.12 and that are assigned to interspecies charge transfer and account for the increased short-circuit current observed. For layers, these components are not as prevalent. This result indicates that greater exciton generation at the dissociating interface and more efficient charge collection in the thin layers is primarily responsible for the improved short-circuit current, a conclusion that is further supported by numerical simulations of the exciton generation rate and charge collection. We also report evidence for an intermediate exciplex state in both types of structures with the greatest yield for blends with of CN-ether-PPV. Overall, the improved performance is due to different processes in the two structures; efficient bulk exciton quenching and charge transfer in blends and enhanced exciton generation and charge collection in layers. The optimization of each photovoltaic heterostructured device relies on this understanding of the mechanisms by which each material architecture achieves high power efficiencies.
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1 February 2006
Research Article|
February 14 2006
Comparison of blended versus layered structures for poly(-phenylene vinylene)-based polymer photovoltaics
S. V. Chasteen;
S. V. Chasteen
Physics Department, ISB,
University of California-Santa Cruz
, Santa Cruz, California 95064
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J. O. Härter;
J. O. Härter
Physics Department, ISB,
University of California-Santa Cruz
, Santa Cruz, California 95064
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G. Rumbles;
G. Rumbles
National Renewable Energy Laboratory
, Center for Basic Science, MS 3216, 1617 Cole Boulevard, Golden, Colorado 80401
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J. C. Scott;
J. C. Scott
IBM Almaden Research Center
, 650 Harry Road, San Jose, California 95120
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Y. Nakazawa;
Y. Nakazawa
Physics Department, ISB,
University of California-Santa Cruz
, Santa Cruz, California 95064
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M. Jones;
M. Jones
National Renewable Energy Laboratory
, Center for Basic Science, MS 3216, 1617 Cole Boulevard, Golden, Colorado 80401
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H.-H Hörhold;
H.-H Hörhold
Institut Für Organische Chemie und Makromolekulare,
University of Jena
, Humboltstrasse 10, Germany
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H. Tillman;
H. Tillman
Institut Für Organische Chemie und Makromolekulare,
University of Jena
, Humboltstrasse 10, Germany
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S. A. Carter
S. A. Carter
Physics Department, ISB,
University of California-Santa Cruz
, Santa Cruz, California 95064
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Electronic mail: [email protected]
J. Appl. Phys. 99, 033709 (2006)
Article history
Received:
August 05 2005
Accepted:
December 14 2005
Citation
S. V. Chasteen, J. O. Härter, G. Rumbles, J. C. Scott, Y. Nakazawa, M. Jones, H.-H Hörhold, H. Tillman, S. A. Carter; Comparison of blended versus layered structures for poly(-phenylene vinylene)-based polymer photovoltaics. J. Appl. Phys. 1 February 2006; 99 (3): 033709. https://doi.org/10.1063/1.2168046
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