Barrierless slow dissociation of photogenerated charge pairs in high-performance polymer–fullerene solar cells

Vithanage, D. A., Matheson, A. B., Pranculis, V., Hedley, G. J. , Pearson, S. J., Gulbinas, V., Samuel, I. D.W. and Ruseckas, A. (2017) Barrierless slow dissociation of photogenerated charge pairs in high-performance polymer–fullerene solar cells. Journal of Physical Chemistry C, 121(26), pp. 14060-14065. (doi: 10.1021/acs.jpcc.7b04868)

Abstract

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 the applied electric field above 12 V/μm and indicates nearly barrierless 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.

• Item Type: Articles
• Additional Information: The 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 MIP85/2015). 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.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Hedley, Dr Gordon
• Authors: Vithanage, D. A., Matheson, A. B., Pranculis, V., Hedley, G. J., Pearson, S. J., Gulbinas, V., Samuel, I. D.W., and Ruseckas, A.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Journal of Physical Chemistry C
• Publisher: American Chemical Society
• ISSN: 1932-7447
• ISSN (Online): 1932-7455