Su J.-MLi Y.-ZChang Y.-HLi M.-ZQiu W.-ZLiu S.-WKEN-TSUNG WONG2021-08-032021-08-03202124686069https://www.scopus.com/inward/record.uri?eid=2-s2.0-85100373556&doi=10.1016%2fj.mtener.2020.100633&partnerID=40&md5=ae9b60c56056aea3eec2e9f2ad8957c8https://scholars.lib.ntu.edu.tw/handle/123456789/575785Four thieno[3,2-b]thiophene (TT)-based donor-π-acceptor–type small-molecule donors DTCPTT, DTCPTT-2CN, DTDCPTT, and DTDCPTT-2CN were synthesized and characterized. A clear structure-property relationship correlating the effects of introducing cyano groups onto the TT and the end-capping groups has been successfully established. DTDCPTT and DTDCPTT-2CN were adopted as electron donors for organic photovoltaics (OPVs) mainly due to the strong intramolecular charge transfer absorption in the visible light region, sufficiently high thermal stability, and appropriate energy level alignment with C70. Moreover, the analyses of crystal structures reveal that DTDCPTT and DTDCPTT-2CN form antiparallel dimer pairs through strong dipolar and non-covalent intermolecular interactions. X-ray structures also indicate that introducing cyano groups onto the TT moiety does not affect the backbone planarity significantly. Compared with DTDCPTT-2CN, the more compact and uniform crystal packing renders DTDCPTT advantageous for exciton dissociation and charge carrier transport. DTDCPTT-based device achieves power conversion efficiency as high as 7.81% and 16.89%, respectively, under simulated AM 1.5G illumination and 500 lux TLD-840 fluorescent lamp illumination, which could be attributed to stronger absorption and better photocurrent extraction. In addition, both devices exhibit high stability under continuous simulated 1 sun illumination for more than 300 h. As far as we know, this is the best performance for vacuum-processed small-molecule indoor OPVs to date. ? 2021 Elsevier LtdCarrier transport; Charge transfer; Conversion efficiency; Crystals; Molecules; Photocurrents; Synthesis (chemical); Thiophene; Energy level alignment; Exciton dissociation; High thermal stability; Intermolecular interactions; Intra-molecular charge transfer; Organic photovoltaics; Power conversion efficiencies; Structure property relationships; Dimers[SDGs]SDG7Carrier transport; Charge transfer; Conversion efficiency; Crystals; Molecules; Photocurrents; Synthesis (chemical); Thiophene; Energy level alignment; Exciton dissociation; High thermal stability; Intermolecular interactions; Intra-molecular charge transfer; Organic photovoltaics; Power conversion efficiencies; Structure property relationships; Dimersjournal article10.1016/j.mtener.2020.1006332-s2.0-85100373556