Symmetry-Induced Ordered Assembly of a Naphthobisthiadiazole-Based Nonfused-Ring Electron Acceptor Enables Efficient Organic Solar Cells

Kyu Chan Song; Woong Sung; Dong Chan Lee; Sein Chung; Hansol Lee; Jaewon Lee; Shinuk Cho; Kilwon Cho

doi:10.1021/acsami.2c13304

Symmetry-Induced Ordered Assembly of a Naphthobisthiadiazole-Based Nonfused-Ring Electron Acceptor Enables Efficient Organic Solar Cells

ACS Appl Mater Interfaces. 2022 Nov 23;14(46):52233-52243. doi: 10.1021/acsami.2c13304. Epub 2022 Nov 10.

Authors

Kyu Chan Song¹, Woong Sung¹, Dong Chan Lee², Sein Chung¹, Hansol Lee³, Jaewon Lee⁴, Shinuk Cho², Kilwon Cho¹

Affiliations

¹ Department of Chemical Engineering, Pohang University of Science and Technology, Pohang37673, Korea.
² Department of Physics and EHSRC, University of Ulsan, Ulsan44610, Korea.
³ Department of Chemical and Biological Engineering, Gachon University, Seongnam13120, Korea.
⁴ Department of Chemical Engineering and Applied Chemistry, Chungnam National University, Daejeon34134, Korea.

PMID: 36355863
DOI: 10.1021/acsami.2c13304

Abstract

Nonfused-ring electron acceptors (NFREAs) have received increasing attention for use in organic solar cells (OSCs) because of their synthetic simplicity and tunable optical spectra. However, their fundamental molecular interactions and the mechanism by which they govern the property-function relations of OSCs remain elusive. Here, to investigate the effects of the structural symmetry of NFREAs, two acceptor-donor-acceptor'-donor-acceptor (A-D-A'-D-A)-type NFREAs, 2,2'-(((naphtho[1,2-c:5,6-c']bis[1,2,5]thiadiazole-5,10-diylbis(4,4-bis(2-butyloctyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-6,2-diyl))bis(methaneylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (NTz-4F) and 2,2'-(((benzo[c][1,2,5]thiadiazole-4,7-diylbis(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-6,2-diyl))bis(methaneylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (BT-4F), are designed and synthesized. They have different A' cores: NTz-4F has a modified centrosymmetric NTz core, whereas BT-4F has a modified axisymmetric BT core. In pristine films, the NTz-4F, which has a centrosymmetric core, shows substantially enhanced intermolecular interaction and microstructural crystalline ordering compared with BT-4F, which has an axisymmetric core. Even in blends with poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8,-dione))] (PBDB-T), NTz-4F retains its highly crystalline structure, whereas BT-4F loses crystalline packing. These changes in NTz-4F result in increased electron transport and suppressed nonradiative voltage loss, resulting in a power conversion efficiency of 9.14% for PBDB-T:NTz-4F vs 7.18% for PBDB-T:BT-4F. This work demonstrates that centrosymmetric-structured cores are promising building blocks for high-performance NFREA-based OSCs.

Keywords: centrosymmetric core; naphthobisthiadiazole; nonfullerene acceptors; nonfused-ring electron acceptors; organic solar cells.