Browsing by Author "Sharma, G. D."

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A New D-A conjugated polymer P(PTQD-BDT) with PTQD acceptor and BDT donor units for BHJ polymer solar cells application
(2015-10-15)
Keshtov, M. L.
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Kuklin, S. A.
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Chen, F. C.
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Khokhlov, A. R.
;
Kurchania, Rajnish
A novel donor-acceptor (D-A) copolymer comprising of weak electron donating BDT moiety and strong 9-(2-octyldodecyl)-8H-pyrrolo[3,4-b] bisthieno[2,3-f:3\',2\'-h] quinoxaline-8,10(9H)-dione (PTQD) unit denoted as P(PTQD-BDT) was synthesized as donor material for polymer solar cells. P(PTQD-BDT) shows a broad visible-near-infrared absorption band with an optical bandgap of 1.74 eV and possesses a relatively low-lying HOMO level at -5.28 eV. Bulk-heterojunction polymer solar cell with the optimized blend of 1:2 (weight ratio) P(PTQD-BDT):PC71BM (processed with chloroform) shows an open circuit voltage of 0.92 V, a short circuit current density of 7.84 mA/cm(2), and a fill factor of 0.50, achieving a power conversion efficiency (PCE) of 3.61%. The PCE has been further improved to 5.55% (J(sc) = 10.34 mA/cm(2), V-oc = 0.88V and FF = 0.61), when 3% vol 1,8-diio-dooctane (DIO) was used as solvent additive for the processing of P(PTQD-BDT):PC71BM blended film. The enhancement in J(sc) is as a result of the appropriate morphology and efficient exciton dissociation into free charge carrier. The increase in PCE has been attributed to the favorable nanoscale morphology for efficient exciton dissociation and charge transport (reduction in the electron to hole mobility ratio). (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2390-2398
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.
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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.
Synthesis and characterization of pi-conjugated copolymers with thieno-imidazole units in the main chain: application for bulk heterojunction polymer solar cells
(2015-01-01)
Keshtov, M. L.
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Godovsky, D. Yu
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Chen, F. C.
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Khokhlov, A. R.
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Siddiqui, S. A.
In this paper the three new narrow bandgap D-A conjugated copolymers P1, P2 and P3 based on different weak donor fused thiophene-imidazole containing derivatives and the same benzothiadiazole acceptor unit were synthesized by Stille cross-coupling polymerization and characterized by H-1 NMR, elemental analysis, GPC, TGA, DSC. These copolymers exhibit intensive absorbance in the range 350-900 nm and the optical bandgap lies in the range of 1.50-1.61 eV, which corresponds to the maximum photon flux of the solar spectrum. The electrochemical bandgap derived from cyclic voltammetry varies within the limits 1.47-1.65 eV and is approximately very close to the optical bandgap. The highest occupied molecular orbital (HOMO) energy level of all copolymers is deep lying (-5.24 eV and -5.37 eV and -5.25 eV for P1, P2 and P2, respectively) which shows that copolymers have good stability in the air and assured a higher open circuit voltage (V-oc) for polymer BHJ solar cells. These copolymers were used as donors along with PC71BM and the BHJ polymer solar cells based on P1:PC71BM, P2:PC71BM and P3:PC71BM processed from chloroform (CF) solvent with 3 v% DIO as an additive showed an overall PCE of 4.55%, 6.76% and 5.16%, respectively.
Synthesis and characterization of two new benzothiadiazole- and fused bithiophene based low band-gap D-A copolymers: Application as donor bulk heterojunction polymer solar cells
(2015-05-18)
Keshtov, M. L.
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Sharma, G. D.
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Kuklin, S. A.
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Ostapov, I. E.
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Godovsky, D. Yu.
Two new narrow bandgap D-A conjugated copolymers P1 and P2 containing different fused thiophene donor unit and same benzothiadiazole acceptor unit were synthesized by Stille cross-coupling polymerization, and characterized by H-1 NMR, elemental analysis and GPC, TGA, DSC. Cyclic voltammetry measurement showed that the HOMO energy level both copolymers is deep lying (-5.10 and -5.35 eV for P1 and P2, respectively) which show that copolymers has good stability in the air and assured a higher open circuit voltage when it photovoltaic application. These copolymer were used as donor along with PC71BM and the BHJ polymer solar cells based on P1:PC71BM and P2:PC71BM processed with chloroform (CF) solvent showed over all PCE of 4.54% and 4.36%, respectively. Additionally, the PCE was improved up to 5.62% and 5.24% for P1:PC71BM and P2:PC71BM active layer processed with DIO (4 v%)/CF solvent. The enhancement in the PCE has been attributed to improved nanoscale morphology and crystalline nature of active layer as well as charge transport in the device with the addition of DIO, due to the higher boiling point of DIO causing slow evaporation rate during the film formation. (C) 2015 Elsevier Ltd. All rights reserved.
Synthesis of alternating D-A1-D-A2 terpolymers comprising two electron-deficient moieties, quinoxaline and benzothiadiazole units for photovoltaic applications
(2016)
Keshtov, M. L.
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Khokhlov, A. R.
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Kuklin, S. A.
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Chen, F. C.
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Nikolaev, A. Y.
Two new regular (D A1 D A2) terpolymers P1 and P2 containing two electron-deficient moieties, quinoxaline and benzothiadiazole, were designed and synthesized. The resulting copolymers exhibit high thermal stability, broad absorption in the range of 300 to 950 nm, low E-g of both 1.36 and 1.57 eV, as well as deep HOMO energy levels of -5.24 and -5.62 eV. Such properties are useful in improving photovoltaic properties. Polymer solar cells (PSCs) based on optimized P1: PC71BM and P2: PC71BM (1 : 2 by weight) active layers with a 3 v% DIO/CF additive displayed a power conversion efficiency (PCE) of 5.28% (Voc of 0.93 V, J(sc) of 10.28 mA cm(-2) and FF of 0.55) and 5.54% (Voc of 0.80 V, J(sc) of 12.18 mA cm(-2) and FF of 0.57), respectively, under illumination of AM1.5G (100 mW cm(-2)). In order to increase the PCE further, the DIO/CF processed active layer was subjected to methanol treatment that resulted in a PCE increase up to 7.13% and 7.59% for the P1: PC71BM and P2: PC71BM based devices, respectively. The methanol treatment increases all of the photovoltaic parameters, which is attributed to the lowering of series resistance, an increase of hole mobility, and reduction of charge recombination due to enlarged built-in potential.
Two new D-A conjugated polymers P(PTQD-Th) and P(PTQD-2Th) with same 9-(2-octyldodecyl)-8H-pyrrolo[3,4-b]bisthieno[2,3-f:3 ',2 '-h]quinoxaline-8,10(9H)-dione acceptor and different donor units for BHJ polymer solar cells application
(2015-09-01)
Keshtov, M. L.
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Kuklin, S. A.
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Chen, F. C.
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Khokhlov, A. R.
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Peregudov, A. S.
We report the synthesis, characterization and photovoltaic properties of bulk heterojunction polymer solar cells of new donor-acceptor conjugated copolymers P(PTQD-Th) and P(PTQD-2Th) that incorporate same strong 9-(2-octyldodecyl)-8H-pyrrolo[3,4-b]bisthieno[2,3-f:3\',2\'-h]quinoxaline-8,10(9H)-dione as strong acceptor and different weak thiophene (Th) and bi-thiophene (2Th) as donors, respectively. Both the copolymers showed suitable unoccupied lowest molecular orbital (LUMO) energy levels, compatible with the LUMO of PC71BM for efficient electron transfer from copolymer to PC71BM in the blended copolymer: PC71BM thin films. Moreover the deeper highest occupied molecular orbital (HOMO) energy levels of both copolymers ensures the high open circuit voltage (V-oc) of the BHJ polymer solar cells. The optimized P(PTQD-Th):PC71BM and P(PTQD-2Th):PC71BM with weight ratio of 1: 2 processed with chloroform solvent showed PCE of 3.65% and 3.96%, respectively. The higher value of J(sc) for the device processed with P(PTQD-2Th):PC71BM as compared to that for P(PTQD-Th):PC71BM, attributed to narrower optical bandgap and broader absorption profile for P(PTQD-2Th) as compared to P(PTQD-Th). The PCE values of polymer solar cells were further improved (5.54% and 5.67% for P(PTQD-Th):PC71BM and P(PTQD-2Th):PC71BM, respectively) when small amounts of solvent additive, i.e. 1,8-diiodoctane (DIO) were used for the processing of active layers. The improved PCE has been attributed to both the enhanced values of short circuit current (J(sc)) and fill factor (FF) due to the better nanomorphology and charge transport, induced by the high boiling point of solvent additive. (C) 2015 Elsevier B.V. All rights reserved.