title: New D-A1-D-A2-Type Regular Terpolymers Containing Benzothiadiazole and Benzotrithiophene Acceptor Units for Photovoltaic Application.
abstract: Two novel regular terpolymers that are of D-A1-D-A2 type and contain benzothiadiazole and 2,5-dibromo-8-dodecanoylbenzo[1,2-b:3,4-b':5,6-d″]trithiophene (P1) or 2,8-dibromo-5-dodecanoylbenzene[1,2-b:3,4-b':5,6-d″]trithiophene (P2) acceptor units with the same thiophene donor were synthesized through Stille coupling, and their optical and electrochemical properties were investigated. The highest occupied molecular orbital (HOMO) and lowest unoccupied (LUMO) molecular orbital energy levels of these terpolymers indicate that there is sufficient LUMO offset with PCBM for efficient exciton dissociation, and their deeper HOMO levels ensure the high open-circuit voltage for the resultant bulk heterojunction solar cells. Measurements on the solar cell devices also confirm that compared to those based on P2 the devices based on P1 possess a higher short-circuit photocurrent (Jsc) as well as a higher fill factor (FF), which is attributed to the lower bandgap and higher hole mobility for P1, whereas the Vocis higher for the devices that are based on P2, which may be a result of P2 having a lower HOMO energy level than P1. The optimized polymer solar cells fabricated using P1:PC71BM (DIO/CF) and P2:PC71BM (CF/DIO) for the active layers showed a PCE of 7.19% and 6.34%, respectively. Atomic force microscopy (AFM) images of P1:PC71BM blend films show that they exhibit more suitable morphology with favorable interpenetrating networks, which favors high Jscand FF. Moreover, P1 exhibits a more crystalline nature than P2 that also favors the charge transport. This may be a result of better molecular packing, more distinct phase separation of the blended films, as well as a reduction of charge recombination.
authors.affiliation: Institute of Organoelement Compounds of the Russian Academy of Sciences , Vavilova St., 28, 119991 Moscow, Russian Federation.
authors.forename: Mukhamed L
authors.initials: ML
authors.lastname: Keshtov
authors.affiliation: Institute of Organoelement Compounds of the Russian Academy of Sciences , Vavilova St., 28, 119991 Moscow, Russian Federation.
authors.forename: Alexei R
authors.initials: AR
authors.lastname: Khokhlov
authors.affiliation: Institute of Organoelement Compounds of the Russian Academy of Sciences , Vavilova St., 28, 119991 Moscow, Russian Federation.
authors.forename: Serge A
authors.initials: SA
authors.lastname: Kuklin
authors.affiliation: Department of Photonics, National Chiao Tung University , Hsinchu, Taiwan 300, Taiwan, ROC.
authors.forename: Fang-Chung
authors.initials: FC
authors.lastname: Chen
authors.affiliation: Nanotechnology and Advanced Materials Laboratory, Department of Chemical Engineering, University of Patras , Patras 26500 GR, Greece.|Molecular Engineering Laboratory, Department of Physics, University of Patras , Patras 26500 GR, Greece.
authors.forename: Emmanuel N
authors.initials: EN
authors.lastname: Koukaras
authors.affiliation: Department of Physics, The LNM Institute for Information Technology , Jamdoli, Jaipur, India.
authors.forename: Ganesh D
authors.initials: GD
authors.lastname: Sharma
keywords: D-A1−D-A2 terpolymer; bulk heterojunction; polymer solar cells; power conversion efficiency; solvent additive