Tsai, C.-H.C.-H.TsaiSu, Y.-A.Y.-A.SuLin, P.-C.P.-C.LinShih, C.-C.C.-C.ShihWu, H.-C.H.-C.WuWEN-CHANG CHENCHU-CHEN CHUEH2019-11-212019-11-21201820507534https://www.scopus.com/inward/record.uri?eid=2-s2.0-85049168970&doi=10.1039%2fc8tc01542b&partnerID=40&md5=1e230f1276a74d1fe73fc1596720303dhttps://scholars.lib.ntu.edu.tw/handle/123456789/431903Ternary organic photovoltaics (OPVs) have recently attracted intense research attention since they have been proven as an effective approach to enhance device performance. We herein describe a new strategy to realize high-performance ternary OPVs by using biaxially extended octithiophene (8T)-based wide-bandgap (Eg) conjugated polymers as the third photoactive component. Owing to the π-π transition of the biaxially extended conjugated side-chains, such polymers exhibit intense absorption in the near-ultraviolet region, in addition to the original intra-charge transfer (ICT) feature arising from the main backbone, revealing a new molecular design for wide-Eg polymers. By further tailoring the polymer backbone with p-type moieties such as thiophene (T) or thienothiphene (TT), two wide-Eg (∼2.0 eV) polymers, P8TT and P8TTT, with absorption wavelengths below 650 nm, were prepared, showing high complementary absorption to the spectra of both the state-of-the-art fullerene-(PTB7-Th:PC71BM) and non-fullerene-based (PBDB-T:ITIC) bulk-heterojunction (BHJ) systems. By providing suitable energy levels, P8TTT was demonstrated to enhance the power conversion efficiency (PCE) of its derived fullerene- and non-fullerene-based ternary blends by 7.58% and 6.60%, respectively, with only a small loading amount (10 wt%). This study manifests a new perspective in wide-Eg material design for realizing efficient ternary BHJ systems. © The Royal Society of Chemistry.[SDGs]SDG7Charge transfer; Energy gap; Fullerenes; Heterojunctions; Polymer solar cells; Solar cells; Absorption wavelengths; Based conjugated polymers; Bulk heterojunction (BHJ); Device performance; Effective approaches; Near-ultraviolet regions; Organic photovoltaics; Power conversion efficiencies; Conjugated polymersjournal article10.1039/c8tc01542b2-s2.0-85049168970