Browsing by Author "Koukaras, Emmanuel N."

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New Alternating D-A(1)-D-A(2) Copolymer Containing Two Electron-Deficient Moieties Based on Benzothiadiazole and 9-(2-Octyldodecyl)-8H-pyrrolo[3,4-b]bisthieno[2,3-f:3 \',2 \'-h]quinoxaline-8,10(9H)-dione for Efficient Polymer Solar Cells
(2016-01-01)
Keshtov, M. L.
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Kuklin, S. A.
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Godovsky, D. Y.
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Khokhlov, A. R.
;
Kurchania, R.
A novel D-A(1)-D-A(2) copolymer denoted as P1 containing two electron withdrawing units based on benzothiadiazole (BT) and 9-(2-octyldodecyl)-8H-pyrrolo[3,4-b] bisthieno[2,3f:3\',2\'-h] quinoxaline-8,10(9H)-dione (PTQD) units was synthesized and characterized. The resulting copolymer exhibits a broad-absorption spectrum, relatively deep lying HOMO energy level (-5.44 eV) and narrow optical bandgap (1.50 eV). Bulk heterojunction (BHJ) polymer solar cells (PSCs) based on P1 as donor and PC71BM as acceptor with optimized donor to acceptor weight ratio of 1: 2 and processed with DIO/CB solvent showed good photovoltaic performance with power conversion efficiency of 6.21% which is higher than that of the device processed without solvent additive (4.40%). The absorption and morphology investigations of the active layers indicated that structural and morphological changes were induced by the solvent additive. This higher power conversion efficiency could bemainly attributed to the absorption enhancement and improved charge transported in the active layer induced by the better nanoscale morphology of the active layer. This study demonstrated that a copolymer with two different acceptor moieties in the backbone may be promising candidate as donor copolymer for solution processed BHJ PSCs. (C) 2015 Wiley Periodicals, Inc.
New D-A1-D-A2-Type Regular Terpolymers Containing Benzothiadiazole and Benzotrithiophene Acceptor Units for Photovoltaic Application
(2016-12-07)
Keshtov, Mukhamed L.
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Khokhlov, Alexei R.
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Kuklin, Serge A.
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Chen, Fang-Chung
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Koukaras, Emmanuel N.
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-d6-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 (J(sc)) as well as a higher fill factor (FF), which is attributed to the lower bandgap and higher hole mobility for P1, whereas the V-oc is 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 PEPC71BM blend films show that they exhibit more suitable morphology with favorable interpenetrating networks, which favors high J(sc) and 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.