Ultrafast Dynamics Group
Frédéric Laquai's Group

Page 12/06/2018 09:51:38

Impact of Structural Polymorphs on Charge Collection and Non-Geminate Recombination in Organic Photovoltaic Devices

Impact of Structural Polymorphs on Charge Collection and Non-Geminate Recombination in Organic Photovoltaic Devices

P. E. Keivanidis, J. I. Khan, L. Katzenmeier, Z. Kan, S. Limbu, M. K. Constantinou, E. Lariou, G. Constantinides, S. C. Hayes, J.–S. Kim, and F. Laquai

J. Phys. Chem. C,

DOI: 10.1021/acs.jpcc.8b09825

P. E. Keivanidis, J. I. Khan, L. Katzenmeier, Z. Kan, S. Limbu, M. K. Constantinou, E. Lariou, G. Constantinides, S. C. Hayes, J.–S. Kim, and F. Laquai
organic photovoltaic, poly(3-hexyl-thiophene), (P3HT)
2018
The formation of different types of structural polymorphs of poly(3-hexyl-thiophene) (P3HT) affects the performance of organic photovoltaic (OPV) devices that use thermally-annealed P3HT:PCBM[60] blend films as photoactive layer. Here it is demonstrated that, when densely-packed and non-densely packed P3HT polymorphs co-exist in the P3HT:PCBM[60] layer, non-geminate charge recombination is fast; however, in a device non-geminate recombination is effectively overruled by efficient and fast charge carrier extraction. In stark contrast, when only a less-densely packed P3HT polymorph is present in the blend, non-geminate charge recombination losses are less pronounced, and the charge carrier extraction efficiency is lower. The antagonistic non-geminate charge recombination and charge carrier extraction processes in these systems are monitored by time-delayed-collection field (TDCF) and ultrafast transient absorption (TA) experiments. Furthermore, resonance Raman spectroscopy reveals that in the absence of the densely-packed P3HT polymorph, the energetic disorder present in the P3HT:PCBM[60] blend is higher. High-resolution atomic force microscopy imaging further identifies pronounced differences in the layer morphology when the polymorph distribution varies between unimodal and bimodal. These results indicate that less-densely packed P3HT polymorphs increase disorder and impede charge collection, leading to a reduction of the device fill factor.