Selenium-substituted non-fullerene acceptors: a route to superior Operational stability for organic bulk heterojunction solar cells.
File(s)
Accepted version
Author(s)
Type
Journal Article
Abstract
Non-fullerene acceptors (NFAs) for organic solar cells (OSCs) have significantly developed over the past five years with continuous improvements in efficiency now over 18%. However, a key challenge still remains in order to fully realize their commercialization potential: the need to extend device lifetime and to control degradation mechanisms. Herein, we investigate the effect of two different molecular engineering routes on the widely utilized ITIC NFA, to tune its optoelectronic properties and interactions with the donor polymer in photoactive blends. Heavier selenium (Se) atoms substitute sulfur (S) atoms in the NFA core in either outer or inner positions, and methyl chains are attached to the end groups. By investigating the effects of these structural modifications on the long-term operational stability of bulk-heterojunction OSC devices, we identify outer selenation as a powerful strategy to significantly increase device lifetime compared to ITIC. Combining outer selenation and methylation results in an impressive 95% of the initial OSC efficiency being retained after 450 h under operating conditions, with an exceptionally long projected half-lifetime of 5600 h compared to 400 h for ITIC. We find that the heavier and larger Se atoms at outer-core positions rigidify the molecular structure to form highly crystalline films with low conformational energetic disorder. It further enhances charge delocalization over the molecule, promoting strong intermolecular interactions among acceptor molecules. Upon methylation, this strong intermolecular interaction stabilizes acceptor domains in blends to be resilient to light-induced morphological changes, thereby leading to superior device stability. Our results highlight the crucial role of NFA molecular structure for OSC operational stability and provide important NFA design rules via heteroatom position and end-group control.
Date Issued
2021-03-26
Date Acceptance
2021-03-23
Citation
ACS Nano, 2021, 15 (4), pp.7700-7712
ISSN
1936-0851
Publisher
American Chemical Society
Start Page
7700
End Page
7712
Journal / Book Title
ACS Nano
Volume
15
Issue
4
Copyright Statement
© 2021 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Nano, after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acsnano.1c01345
Sponsor
Engineering and Physical Sciences Research Council
National Research Foundation of Korea (NRF)
Engineering and Physical Sciences Research Council
Identifier
https://www.ncbi.nlm.nih.gov/pubmed/33769786
Grant Number
EP/L016702/1
NRF-2017K1A1A2013153
EP/T028513/1
Subjects
bulk-heterojunction organic solar cells
crystallinity
heteroatoms
non-fullerene acceptors
photostability
Publication Status
Published
Coverage Spatial
United States
Date Publish Online
2021-03-26