Relating Recombination, Density of States, and Device Performance in an Efficient Polymer:Fullerene Organic Solar Cell Blend
Article first published online: 12 JUN 2013
Copyright © 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Advanced Energy Materials
Volume 3, Issue 9, pages 1201–1209, September, 2013
How to Cite
Hawks, S. A., Deledalle, F., Yao, J., Rebois, D. G., Li, G., Nelson, J., Yang, Y., Kirchartz, T. and Durrant, J. R. (2013), Relating Recombination, Density of States, and Device Performance in an Efficient Polymer:Fullerene Organic Solar Cell Blend. Adv. Energy Mater., 3: 1201–1209. doi: 10.1002/aenm.201300194
- Issue published online: 10 SEP 2013
- Article first published online: 12 JUN 2013
- Manuscript Revised: 19 MAR 2013
- Manuscript Received: 21 FEB 2013
- Funded Access
- bulk heterojunction;
- organic solar cell
We explore the interrelation between density of states, recombination kinetics, and device performance in efficient poly[4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-4-(2-ethylhexyloxy-1-one)thieno[3,4-b]thiophene-2,6-diyl]:[6,6]-phenyl-C71-butyric acid methyl ester (PBDTTT-C:PC71BM) bulk-heterojunction organic solar cells. We modulate the active-layer density of states by varying the polymer:fullerene composition over a small range around the ratio that leads to the maximum solar cell efficiency (50–67 wt% PC71BM). Using transient and steady-state techniques, we find that nongeminate recombination limits the device efficiency and, moreover, that increasing the PC71BM content simultaneously increases the carrier lifetime and drift mobility in contrast to the behavior expected for Langevin recombination. Changes in electronic properties with fullerene content are accompanied by a significant change in the magnitude or energetic separation of the density of localized states. Our comprehensive approach to understanding device performance represents significant progress in understanding what limits these high-efficiency polymer:fullerene systems.