Barrierless slow dissociation of photogenerated charge pairs in high-performance polymer-fullerene solar cells
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Broadband transient absorption spectroscopy is combined with ultrafast carrier drift measurements to study dissociation of photogenerated charge pairs in efficient photovoltaic blends of the electron donating polymer PTB7 with the acceptor PC71BM. A high ensemble-average mobility sum of electrons and holes is observed which is independent of applied electric field above 12 V/μm and indicates nearly barrier-less pair dissociation at room temperature on a picosecond time scale. High efficiency of pair dissociation in this material is achieved by a combination of high electron mobility in fullerene clusters and hole delocalization along the polymer chain which increases by 30% during dissociation. Our results suggest a predominantly diffusive charge pair dissociation mechanism which requires persistent mobility of both carriers and preferably some delocalization of at least one of them.
Vithanage , D A , Matheson , A B , Pranculis , V , Hedley , G J , Pearson , S J , Gulbinas , V , Samuel , I D W & Ruseckas , A 2017 , ' Barrierless slow dissociation of photogenerated charge pairs in high-performance polymer-fullerene solar cells ' , Journal of Physical Chemistry C , vol. 121 , no. 26 , pp. 14060-14065 . https://doi.org/10.1021/acs.jpcc.7b04868
Journal of Physical Chemistry C
© 2017, American Chemical Society. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at pubs.acs.org / https://doi.org/10.1021/acs.jpcc.7b04868
DescriptionThe work in St Andrews was supported by the Engineering and Physical Sciences Research Council (grants EP/L017008/1, EP/J009016/1 and EP/G03673X/1) and the European Research Council (grant 321305). The work in Vilnius was supported by the Research Council of Lithuania (project MIP-85/2015). I.D.W.S. acknowledges support from a Royal Society Wolfson Research Merit Award. D.A.V. is grateful to Supergen SuperSolar Hub for the travel grant. The research data supporting this publication can be accessed at http://dx.doi.org/10.17630/7ec84b4b-d2ab-493c-aaf6-5503a44c0eb5
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