Journal
ORGANIC ELECTRONICS
Volume 10, Issue 7, Pages 1275-1281Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.orgel.2009.07.002
Keywords
Polymer; Solar cells; Molecular weight; Dissociation; Polyfluorene
Funding
- SenterNovem [EOS LT 03026]
- Dutch Polymer Institute (DPI) [524]
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The effect of the molecular weight of poly[9,9-didecanefluorene-alt-(bis-thienylene) benzothiadiazole] (PF10TBT) on the photovoltaic performance of fullerene-based bulk heterojunction solar cells is investigated. An increase in molecular weight of two orders of magnitude results in a 30% increase of the short-circuit current and a rise of the fill factor from 0.45 to 0.63. Electron and hole transport are found to be virtually unaffected by changing molecular weight, which means that space-charge effects do not play a role in low molecular weight devices. Using optical modeling and numerical device simulations, we demonstrate that at low molecular weight the efficiency is mainly limited by a short lifetime of bound electron-hole pairs. This short lifetime prohibits efficient dissociation and is attributed to a deficiency in phase separation for low molecular weights. (C) 2009 Elsevier B.V. All rights reserved.
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