Precise Modulation of Reorganization Energy through Methyl Substitution for High Performance Organic Solar Cells

Li Chen; Chaoyue Zhao; Joshua Yuk Lin Lai; Rongkun Zhou; Aleksandr Sergeev; Kam Sing Wong; Huawei Hu; Zilong Zheng; Han Yu; Sai Ho Pun; Guangye Zhang; He Yan

doi:10.1002/advs.202505143

Precise Modulation of Reorganization Energy through Methyl Substitution for High Performance Organic Solar Cells

Adv Sci (Weinh). 2025 Jul 7:e05143. doi: 10.1002/advs.202505143. Online ahead of print.

Authors

Affiliations

¹ Department of Chemistry and Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction, The Hong Kong University of Science and Technology, Hong Kong, 999077, P. R. China.
² College of Materials Science and Engineering, Beijing University of Technology, Beijing, 100124, P. R. China.
³ Department of Physics and William Mong Institute of Nano Science and Technology, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, 999077, China.
⁴ State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai, 201620, China.
⁵ College of New Materials and New Energies, Shenzhen Technology University, Shenzhen, 518118, P. R. China.

PMID: 40621628
DOI: 10.1002/advs.202505143

Abstract

Efficient charge transport and minimized energy loss are critical for advancing the performance of organic solar cells (OSCs). In this study, a series of quinoxaline-based electron acceptors, BQx-MeF, BQx-MeCl, and BQx-MeBr, featuring methyl and halogen substitutions is designed and synthesized to systematically modulate reorganization energy (λ) and film morphology. Quantum chemical calculations confirmed that methylation effectively reduces λ by limiting structural relaxation, leading to suppressed non-radiative recombination energy loss (ΔE_nr) and improved charge transport. Among the synthesized materials, BQx-MeCl exhibited the lowest energy loss and the most balanced electron and hole mobilities, resulting in a superior power conversion efficiency (PCE) of 19.2% in a binary device. In optimized ternary OSCs, BQx-MeCl further reached a remarkable PCE of 19.6%. This enhancement is attributed to optimized molecular stacking, improved film morphology, and reduced trap-assisted recombination. These findings highlight the pivotal role of molecular design in lowering reorganization energy to minimize energy losses and maximize charge collection, offering an effective strategy for the development of high-efficiency OSCs.

Keywords: methyl substitution; organic solar cells; quinoxaline; reorganization energy; small molecule acceptor.

Abstract

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