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ECN publication
Impact of molecular weight on charge carrier dissociation in solar cells from a polyfluorene derivative
Moet, D.J.D.; Lenes, M.; Kotlarski, J.D.; Veenstra, S.C.; Sweelssen, J.; Koetse, M.M.; Boer, B. de; Blom, P.W.M.
Published by: Publication date:
ECN Solar Energy 9-7-2009
ECN report number: Document type:
ECN-W--10-001 Article (scientific)
Number of pages:

Published in: Organic Electronics (Elsevier), , 2009, Vol.10, p.1275-1281.

The effect of the molecular weight of poly[9,9-dicecanefluorene-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 devices. Using optical modeling and numerical device simulations, we demonstrate that a 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.

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