Tuning conjugated chain ends in small molecular acceptors for enhancing molecular packing in binary blend acceptors and inducing high efficiency in planar junction organic photovoltaics

Lu, Tzu-ChingTzu-ChingLuChang, BinBinChangHuang, Chi-TingChi-TingHuangKao, Jui-ChengJui-ChengKaoChen, Bo-HanBo-HanChenTsai, Ching-EnChing-EnTsaiChen, Chung-HaoChung-HaoChenYang, Shang-DaShang-DaYangJYH PIN CHOULo, Yu-ChiehYu-ChiehLoWei, Kung-HwaKung-HwaWei2026-03-022026-03-02202620507488https://www.scopus.com/record/display.uri?eid=2-s2.0-105030527545&origin=resultslisthttps://scholars.lib.ntu.edu.tw/handle/123456789/736050A series of AD'A'D'A type small-molecule acceptors based on the dithienothiophen-pyrrolo-benzothiadiazole core and dicyanomethylene-3-indanone (Y5-IC) with different types of conjugated chain end units such as thiophene (-T), thieno[3,2-b]thiophene (-TT), and dithieno[3,2-b:2′,3′-d]thiophene (-TTT), namely Y5-IC-Tx (x = 1–3), are designed and synthesized. These Y5-IC-Tx are blended with small molecule acceptor L8-BO, respectively, for forming acceptor layers that are subsequently deposited onto PM6 donor to form PM6/L8-BO : Y5-IC-Tx planar junction active layers. Among all devices, the champion planar junction PM6/L8-BO : Y5-IC-TT (wt ratio 8 : 2) device exhibits a power conversion efficiency (PCE) value of 19.3% and a high fill factor value of 79%, a substantial increase over the PCE value of 17.4% and fill factor value of 74% for the PM6/L8-BO control device. These enhancements result from additional light absorption of Y5-IC-TT with its optimal molecular packing with L8-BO that improves charge transport in the device. The density functional theory calculation results reveal that Y5-IC-TT has the smallest dihedral angle of 14.87° and the largest binding energy value of −1.5 eV with L8-BO in both anti-parallel and parallel configurations among all cases, being consistent with the enhanced crystalline coherence length value of 18.8 Å for L8-BO : Y5-IC-TT as compared to 17.1 Å for the L8-BO film from wide-angle X-ray scattering. These types of binary alloy blend acceptors that involve molecular engineering of conjugated end-groups as the acceptor layer strategy effectively improve the PCE of planar junction organic photovoltaics, providing pathways for the development of high-performance organic photovoltaic devices. This journal is © The Royal Society of Chemistry, 2026falseTuning conjugated chain ends in small molecular acceptors for enhancing molecular packing in binary blend acceptors and inducing high efficiency in planar junction organic photovoltaicsjournal article10.1039/d5ta09626j2-s2.0-105030527545