Spectral dependence of the internal quantum efficiency of organic solar cells: Effect of charge generation pathways

Armin, Ardalan, Kassal, Ivan, Shaw, Paul E., Hambsch, Mike, Stolterfoht, Martin, Lyons, Dani M., Li, Jun, Shi, Zugui, Burn, Paul L. and Meredith, Paul (2014) Spectral dependence of the internal quantum efficiency of organic solar cells: Effect of charge generation pathways. Journal of The American Chemical Society, 136 32: 11465-11472. doi:10.1021/ja505330x

Author Armin, Ardalan
Kassal, Ivan
Shaw, Paul E.
Hambsch, Mike
Stolterfoht, Martin
Lyons, Dani M.
Li, Jun
Shi, Zugui
Burn, Paul L.
Meredith, Paul
Title Spectral dependence of the internal quantum efficiency of organic solar cells: Effect of charge generation pathways
Journal name Journal of The American Chemical Society   Check publisher's open access policy
ISSN 0002-7863
Publication date 2014-08
Year available 2014
Sub-type Article (original research)
DOI 10.1021/ja505330x
Open Access Status
Volume 136
Issue 32
Start page 11465
End page 11472
Total pages 8
Place of publication Washington, DC United States
Publisher American Chemical Society
Collection year 2015
Language eng
Formatted abstract
The conventional picture of photocurrent generation in organic solar cells involves photoexcitation of the electron donor, followed by electron transfer to the acceptor via an interfacial charge-transfer state (Channel I). It has been shown that the mirror-image process of acceptor photoexcitation leading to hole transfer to the donor is also an efficient means to generate photocurrent (Channel II). The donor and acceptor components may have overlapping or distinct absorption characteristics. Hence, different excitation wavelengths may preferentially activate one channel or the other, or indeed both. As such, the internal quantum efficiency (IQE) of the solar cell may likewise depend on the excitation wavelength. We show that several model high-efficiency organic solar cell blends, notably PCDTBT:PC70BM and PCPDTBT:PC60/70BM, exhibit flat IQEs across the visible spectrum, suggesting that charge generation is occurring either via a dominant single channel or via both channels but with comparable efficiencies. In contrast, blends of the narrow optical gap copolymer DPP-DTT with PC70BM show two distinct spectrally flat regions in their IQEs, consistent with the two channels operating at different efficiencies. The observed energy dependence of the IQE can be successfully modeled as two parallel photodiodes, each with its own energetics and exciton dynamics but both having the same extraction efficiency. Hence, an excitation-energy dependence of the IQE in this case can be explained as the interplay between two photocurrent-generating channels, without recourse to hot excitons or other exotic processes.
Keyword Hot exciton discussion
Photovoltaic Devices
High mobility
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mathematics and Physics
Official 2015 Collection
School of Chemistry and Molecular Biosciences
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Citation counts: TR Web of Science Citation Count  Cited 20 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 22 times in Scopus Article | Citations
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Created: Fri, 08 Aug 2014, 12:00:46 EST by Mrs Louise Nimwegen on behalf of School of Chemistry & Molecular Biosciences