New ultra low bandgap thiadiazolequinoxaline-based D-A copolymers for photovoltaic applications |
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| Affiliation: | 1. Institute of Organoelement Compounds of the Russian Academy of Sciences, Vavilova St., 28, Moscow 119991, Russian Federation;2. Nanotechnology and Advanced Materials Laboratory, Department of Chemical Engineering, University of Patras, Patras 26500 GR, Greece;3. Molecular Engineering Laboratory, Department of Physics, University of Patras, Patras 26500 GR, Greece;4. Department of Physics, The LNM Institute of Information Technology, Jamdoli, Jaipur 302031, Rajasthan, India;1. Henan Key Laboratory of Polyoxometalate Chemistry, College of Chemistry and Chemical Engineering, Henan University, China;2. Institute of Metal Research, Chinese Academy of Sciences, Division of Materials for Special Environments, China;3. Renewable Bioproduct Institute, Georgia Institute of Technology, United States;1. State Key Laboratory for Powder Metallurgy, Central South University, Changsha 410083, China;2. College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China;3. Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China;1. Paul Scherrer Institute (PSI), CH-5232, Villigen, Switzerland;2. Department of Applied Physics, Eindhoven University of Technology, P. O. Box 513, 5600 MB, Eindhoven, The Netherlands;3. Holst Centre, TNO-The Dutch Organization for Applied Scientific Research, High Tech Campus 31, 5656 AE, Eindhoven, The Netherlands;4. Max Planck Institute for Polymer Research, Ackermannweg 10, 55128, Mainz, Germany;5. Department of Physics, Chemistry and Biology (IFM), Linkping University, P. O. Box SE-581 83, Linkping, Sweden;6. Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-8600, Dübendorf, Switzerland |
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| Abstract: | 
In this communication, we designed two low bandgap D-A copolymers with same fluorinated thiadiazoloquinoxaline (TDQ) as acceptor and different donor units benzo[2,1-b;3,4-b′]dithiophene (P1) and benzo[1,2-b:4,5-b′]dithiophene (P2). P1 and P2 exhibit broad absorption profiles covering from 350 nm to 1150 nm and 350–950 nm, respectively with optical bandgaps of 1.06 eV and 1.18 eV, respectively. Both copolymers showed deep highest occupied molecular orbitals (HOMO), i.e. −5.38 eV and −5.26 eV, for P1 and P2. Their photovoltaic properties were evaluated using conventional devices with a structure of ITO/PEDOT:PSS/copolymer:PC71BM/Al. After the optimizations of the copolymer to PC71BM weight ratios, and concentration of the solvent additive (DIO), the devices showed overall power conversion efficiencies of 4.03% and 5.42% for the P1 and P2 based devices, respectively. The higher value of PCE of the P2 based device is attributed to the higher values of Jsc and FF, that is related to the higher hole mobility and better exciton dissociation efficiency. Although the PCEs of these devices are moderate, these ultra low band gap copolymers can be used for their potential application in tandem polymers solar cells. Finally, methanol treatment of the active layer was adopted to increase the PCE of the P2:PC71BM based polymer solar cells that resulted in an improved PCE up to 6.93%. |
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| Keywords: | Ultra low bandgap copolymers Bulk heterojunction polymer solar cells Power conversion efficiency Solvent additives |
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