Improved photovoltaic performance of a nonfullerene acceptor based on a benzo[]thiophene fused end group with extended π-conjugation

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2019-04, Vol.7 (16), p.9822-983
• Main Authors: Yang, Kun, Liao, Qiaogan, Koh, Chang Woo, Chen, Jianhua, Su, Mengyao, Zhou, Xin, Tang, Yumin, Wang, Yang, Zhang, Youming, Woo, Han Young, Guo, Xugang
• Format: Article
• Language: English
• Subjects: Absorption; Absorption spectra; Acceptor materials; Benzothiophene; Circuits; Conjugation; Construction standards; Electron mobility; Electrons; Energy conversion efficiency; Energy levels; Malononitrile; Molecular orbitals; Morphology; Open circuit voltage; Photoelectric effect; Photoelectric emission; Photovoltaic cells; Photovoltaics; Short circuit currents; Short-circuit current; Solar cells; Solar power
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c9ta01111k

A new indacenodithiophene-based acceptor-donor-acceptor (A-D-A) type nonfullerene acceptor material ITBTC , featuring a conjugation-extended benzo[ b ]thiophene-fused end group, was designed and synthesized. Compared to the well known phenyl-fused ITIC acceptor containing a 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC) end group, incorporation of an additional electron-rich thiophene into the IC moiety decreased the electron-accepting strength of the end group and increased the intermolecular interactions of ITBTC molecules. As a result, ITBTC exhibited an elevated lowest unoccupied molecular orbital, an improved electron mobility, and a more favorable blend film morphology. Despite its slightly blue-shifted absorption, the photocurrent of ITBTC -based devices was well-maintained due to the extra absorption band in the short wavelength range, which is induced by its conjugation-extended end group. Benefitting from these characteristics, the ITBTC -based solar cells achieved an enhanced power conversion efficiency (PCE) of 10.99% with a simultaneously improved open-circuit voltage ( V oc , 0.94 V) and fill factor (FF, 71.3%) and well-maintained short-circuit current density ( J sc , 16.37 mA cm −2 ), compared to those of the ITIC -based devices (PCE of 9.53%). These results suggest that extending the π-conjugation of end group through thiophene incorporation is an efficient approach for optimizing both the energy level alignment and intermolecular interaction of the acceptor materials while maintaining their efficient light-harvesting ability. Our study also demonstrates the great potential of the new benzo[ b ]thiophene-fused end group for constructing high-performance nonfullerene acceptors and provided insight into overcoming the trade-off between J sc and V oc to realize simultaneously enhanced photovoltaic parameters. By utilizing a conjugation extended benzo[ b ]thiophene-fused end group, a nonfullerene acceptor was developed with simultaneously improved photovoltaic parameters.