Organic Photovoltaics: The Impact of Non-fullerene Acceptors

Jean-Luc Bredas, University of Arizona

With the emergence of non-fullerene acceptors five years ago, the power conversion efficiency of organic solar cells (OSCs) has increased remarkably, from some 12% to over 18%. In OSCs, the active layers consist of bulk-heterojunctions, that is blends of an electron acceptor and an electron donor component. The inter-molecular charge transfer electronic states that appear at the donor-acceptor interfaces play a crucial role in the exciton-dissociation, charge-separation, and charge-recombination processes [1].

In this presentation, we will discuss how the combination of state-of-the-art electronic structure calculations and molecular dynamics simulations allows a reliable description of (i) the molecular packing at the donoracceptor interfaces; (ii) the nature and energetic distribution of the charge-transfer electronic states; and (iii) the rates of radiative and nonradiative charge recombinations. In all, the results provide a molecular understanding of the factors that contribute to high efficiency [2-4] and pave the way towards reaching the Shockley-Queisser limit.

This work is funded by the Office of Naval Research.

[1]    “Charge-Transfer Electronic States in Organic Solar Cells”, V. Coropceanu, X.K. Chen, T.H. Wang, Z.L. Zheng, and J.L. Brédas, Nature Reviews Materials, 4, 689-707 (2019). 
[2]    “Organic Photovoltaics: Relating Chemical Structure, Local Morphology, and Electronic Properties”, T. Wang, G. Kupgan, and J.L. Brédas, Trends in Chemistry, 2, 535-554 (2020). 
[3]    “Organic Solar Cells Based on Non-fullerene Small-Molecule Acceptors: Impact of Substituent Position”, T. Wang and J.L. Brédas, Matter, 2, 119-135 (2020). 
[4]    “Delocalization of Exciton and Electron Wavefunction in Non-fullerene Acceptor Molecules Enables Efficient Organic Solar Cells”, G. Zhang, X.K. Chen, J. Xia, P.C.Y. Chow, M. Ren, G. Kupgan, X. Jiao, C.C.S. Chan, X. Du, R. Xia, Z. Chen, J. Yuan, Y. Zhang, S. Zhang, Y. Liu, Y. Zou, H. Yan, K.S. Wong, V. Coropceanu, N. Li, C.J. Brabec, J.L. Brédas, H.L. Yip, and Y. Cao, Nature Communications, 11, 3943 (2020); DOI: 10.1038/s41467-020-17867-1.