High-Efficiency Organic Photovoltaics with Two-Dimensional Conjugated Benzodithiophene-Based Regioregular Polymers

We synthesized and characterized two kinds of regioregular polymers that were based on thieno[3,4- b ]thiophene as an electron-accepting unit and benzo[1,2- b:4,5- b ′]dithiophene as the electron-donating unit with different side chain, alkylthio and alkyl thiophenes, named rr-PTBS and rr-PTB7-Th, respectively. Because of the partial introduction of the alkylthio thiophene side chain, rr-PTBS showed red-shifted absorption and a deeper HOMO level compared to those of rr-PTB7-Th. In addition, both rr-PTBS:PC 71 BM and rr-PTB7-Th:PC 71 BM blended films showed face-on orientations stronger than those of regiorandom PTB7-Th. However, the rr-PTB7-Th:PC 71 BM blended film showed a peak in the out-of-plane direction much weaker than those of rr-PTBS:PC 71 BM and PTB7-Th:PC 71 BM blended films. Moreover, the rr-PTBS:PC 71 BM blended film exhibited charge carrier mobility (μ e /μ h ∼ 1.01) much more balanced than that of the rr-PTB7-Th:PC 71 BM blended film (μ e /μ h ∼ 1.23). The bulk-heterojunction organic photovoltaic (OPV) device based on rr-PTBS and the 1,8-diiodooctane additive showed a high power conversion efficiency (PCE) of 8.68%, while the OPV device based on rr-PTB7-Th and the 1,8-diiodooctane additive showed a PCE of 7.04%. Finally, an OPV device using rr-PTBS, the diphenyl ether additive, and Micro Lens Film exhibited a short-circuit current ( J sc ) of 19.72 mA/cm 2, an open-circuit voltage ( V oc ) of 0.82 V, and a fill factor (FF) of 63.82%, thus resulting in a PCE of 10.31%.