The synergistic effects of central core size and end group engineering on performance of narrow bandgap nonfullerene acceptors

Journal Article · 04 February 2022 · Chemical Engineering Journal

DOI: https://doi.org/10.1016/j.cej.2022.135020 · OSTI ID:1981559

Liao, Xunfan ^[1]; Pei, Hongqiao ^[2]; Zhao, Heng ^[3]; Cui, Yongjie ^[1]; Li, Lei ^[2]; Shi, Xueliang ^[4]; Zhu, Peipei ^[2]; Ma, Wei ^[3]; Chen, Yiwang  ^[2]; Jen, Alex K.-Y. ^[5]

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1. Jiangxi Normal University, Nanchang (China); Donghua University, Shanghai (China)
2. Jiangxi Normal University, Nanchang (China)
3. Xi'an Jiaotong Univ., Shaanxi (China)
4. Donghua University, Shanghai (China)
5. City Univ. of Hong Kong, Kowloon (Hong Kong)

Understanding the relationship between the molecular structure and photoelectric properties of fused-ring non-fullerene acceptors (NFAs) is of far-reaching significance to the development of organic solar cells (OSCs). Herein, six NFAs based on multiple thiophenes (4 T, 6 T and 8 T) are employed to systematically probe the synergistic effects of extending central core size and terminal fluorination. The absorption results manifest that the molecular absorption is comprehensively affected by molecular crystallinity, planarity, conjugation length and intramolecular electron push–pull effect, simultaneously. The intensity of electron push–pull effect is not only related to the electron-donating ability of central core and the electron-withdrawing ability of end group, but also may be related to the distance between the positive and negative centers. The extension of central core leads to the more planar backbone and stronger crystallinity of NFAs, and less energy loss (E_loss) in its based OSC. Compared with the extension of central core, terminal fluorination has a greater impact on molecular photoelectric properties. The terminal fluorination significantly enhances the push–pull effect, lowers the energy levels, and slightly increases the vibrational relaxation. As a result, the strongest crystallinity and coplanarity of 8TIC-4F lead to a low vibrational relaxation of 0.18 eV, which makes PTB7-Th:8TIC-4F device exhibit a small E_loss of 0.51 eV and a high efficiency of 10.4%. In addition, the fluorinated 6TIC-4F with suitable core size exhibits suitable energy level, absorption, crystallization, and phase separation morphology, making its as-cast device up to 11.61% efficiency. Finally, to the best of the authors’ knowledge, the PCE of 11.61% for PTB7-Th:6TIC-4F based device without any treatment is one of the highest values reported for the NAFs with over 1000 nm absorption.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
• Sponsoring Organization: Donghua University; Jiangxi Provincial Natural Science Foundation; National Natural Science Foundation of China (NSFC); Shanghai Education Development Foundation; Shanghai Municipal Education Commission; Thousand Talents Plan of Jiangxi Province; USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1981559
• Journal Information: Chemical Engineering Journal, Journal Name: Chemical Engineering Journal Journal Issue: P2 Vol. 435; ISSN 1385-8947
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Central core size
End group fluorination
Engineering
Nonfullerene acceptors
Organic solar cells
Push-pull effect