Hybridization of local exciton and charge-transfer states reduces non-radiative voltage losses in organic solar cells
File(s)Non-Radiative_Hybridization_Updated_Pub_2.docx (379.5 KB)
Accepted version
Author(s)
Type
Journal Article
Abstract
A number of recent studies have shown that the nonradiative voltage losses in organic solar cells can be suppressed in systems with low energetic offsets between donor and acceptor molecular states, but the physical reasons underpinning this remain unclear. Here, we present a systematic study of 18 different donor/acceptor blends to determine the effect that energetic offset has on both radiative and nonradiative recombination of the charge-transfer (CT) state. We find that, for certain blends, low offsets result in hybridization between charge-transfer and lowest donor or acceptor exciton states, which leads to a strong suppression in the nonradiative voltage loss to values as low as 0.23 V associated with an increase in the luminescence of the CT state. Further, we extend a two-state CT-state recombination model to include the interaction between CT and first excited states, which allows us to explain the low nonradiative voltage losses as an increase in the effective CT to ground state oscillator strength due to the intensity borrowing mechanism. We show that low nonradiative voltage losses can be achieved in material combinations with a strong electronic coupling between CT and first excited states and where the lower band gap material has a high oscillator strength for transitions from the excited state to the ground state. Finally, from our model we propose that achieving very low nonradiative voltage losses may come at a cost of higher overall recombination rates, which may help to explain the generally lower FF and EQE of highly hybridized systems.
Date Issued
2019-04-17
Date Acceptance
2019-03-18
Citation
Journal of the American Chemical Society, 2019, 141 (15), pp.6362-6374
ISSN
1520-5126
Publisher
American Chemical Society
Start Page
6362
End Page
6374
Journal / Book Title
Journal of the American Chemical Society
Volume
141
Issue
15
Copyright Statement
© 2019 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of the American Chemical Society, after peer review and technical editing by the publisher. To access the final edited and published work see https://dx.doi.org/10.1021/jacs.9b01465
Sponsor
Engineering and Physical Sciences Research Council
British Council (Turkey)
Engineering & Physical Science Research Council (EPSRC)
Engineering & Physical Science Research Council (EPSRC)
Identifier
https://www.ncbi.nlm.nih.gov/pubmed/30882218
Grant Number
IL4 337323
EP/M025020/1
EP/P005543/1
Subjects
Science & Technology
Physical Sciences
Chemistry, Multidisciplinary
Chemistry
DONOR-ACCEPTOR INTERFACES
EFFICIENT NON-FULLERENE
ELECTRON-TRANSFER
POLYMER
SEPARATION
RECOMBINATION
ENERGY
FLUORINATION
ABSORPTION
DELOCALIZATION
General Chemistry
03 Chemical Sciences
Publication Status
Published
Coverage Spatial
United States
Date Publish Online
2019-03-18