Two new small molecules, C3T-BDTP and C3T-BDTP-F with alkoxyphenyl-substituted benzo[1,2-b:4,5-b']dithiophene (BDT) and meta-fluorinated-alkoxyphenyl-substituted BDT as the central donor blocks, respectively, have been synthesized and used as donor materials in organic solar cells (OSCs). With the addition of 0.4% v/v 1,8-diiodooctane (DIO), the blend of C3T-BDTP-F/PC71BM showed a higher hole mobility of 8.67 × 10(-4) cm(2) V(-1) s(-1) compared to that of the blend of C3T-BDTP/PC71BM. Two types of interlayers, zirconium acetylacetonate (ZrAcac) and perylene diimide (PDI) derivatives (PDINO and PDIN), were used to further optimize the performance of OSCs. With a device structure of ITO/PEDOT:PSS/donor:PC71BM/PDIN/Al, the OSCs based on C3T-BDTP delivered a satisfying power conversion efficiency (PCE) of 5.27% with an open circuit voltage (V(oc)) of 0.91 V, whereas the devices based on C3T-BDTP-F showed an enhanced PCE of 5.42% with a higher V(oc) of 0.97 V.

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Two new copolymers named TBFPF-BT and TBFPF-BO, composing of a fluorine substituted thieno[2,3-f]benzofuran donor unit and benzothiadiazole/benzooxadiazole acceptor unit, have been synthesized as the donor materials for polymer solar cell (PSC) application. Both polymers presented wide absorptions (300~800 nm) in the UV-Vis region. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels were -5.28/-3.60 eV and -5.38/-3.69 eV for TBFPF-BT and TBFPF-BO, respectively. PSCs with the blends of TBFPF-BT/TBFPF-BO and PC 71 BM (1:2, w/w) as photoactive layers exhibited relatively low photovoltaic performances. After optimizing with 1% 1,8-diiodooctane (DIO) as additive, dramatic changes in short-circuit current density (J sc ) and fill factor (FF) were occurred with PCE up to 6.80% and 5.98% under AM 1.5, 100 mW cm −2 for TBFPF-BT and TBFPF-BO, respectively.Compared to TBFPF-BO, the higher PCE mainly benefits from the higher hole mobility and better morphology for TBFPF-BT and PC 71 BM blend film.

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