Comparison of blended versus layered structures for poly(p-phenylene vinylene)-based polymer photovoltaics

被引:32
作者
Chasteen, SV [1 ]
Härter, JO
Rumbles, G
Scott, JC
Nakazawa, Y
Jones, M
Hörhold, HH
Tillman, H
Carter, SA
机构
[1] Univ Calif Santa Cruz, Dept Phys, ISB, Santa Cruz, CA 95064 USA
[2] Ctr Basic Ctr, Natl Renewable Energy Lab, Golden, CO 80401 USA
[3] IBM Corp, Almaden Res Ctr, San Jose, CA 95120 USA
[4] Univ Jena, Inst Organ Chem & Makromol, D-6900 Jena, Germany
关键词
D O I
10.1063/1.2168046
中图分类号
O59 [应用物理学];
学科分类号
摘要
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 (>3 mA/cm(2)) and power efficiencies (similar to 1% 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 (similar to 20%) 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 0.78 ns 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 50 wt % 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. (c) 2006 American Institute of Physics.
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页数:10
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