Browsing by Author "Keshtov, M. L."

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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.
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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
Conjugated poly(fluoroalkyl 3-thienylacetate)s synthesized in supercritical carbon dioxide
(2012-04-01)
Keshtov, M. L.
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Lopatin, A. M.
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Marochkin, D. V.
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Chen, Fang-Chung
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Khokhlov, A. R.
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.
New conjugated electroluminescent triphenylamine-containing polymers with side-chain pyridin-2-ylimidazo[1,5-a]pyridine groups for polymer light-emitting diodes
(2013-06-01)
Keshtov, M. L.
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Chen, Fang-Chung
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Maltsev, E. I.
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Marochkin, D. V.
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Kochurov, V. S.
New iridium-containing conjugated polymers for polymer solar cell applications
(2018-11-07)
Keshtov, M. L.
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Kuklin, S. A.
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Konstantinov, I. O.
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Chen, Fang-Chung
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Xie, Zhi-yuan
A series of novel donor-acceptor (D-A) copolymers P1-P5 with iridium-complexed moieties in their side chains have been synthesized on the basis of a new iridium-containing monomer. The results obtained show that P1-P5 have good thermal stability (317-347 degrees C) for photovoltaic applications. These copolymers absorb visible light in a broad spectral range up to 680 nm. The optical bandgaps of P1-P5 are in the range of 1.96-2.08 eV, respectively. The HOMO and LUMO energy levels of the polymers P1-P5 estimated from cyclic voltammetry measurements indicate that these copolymers are suitable as electron donors along with PC71BM as an electron acceptor for bulk heterojunction polymer solar cells. BHJ polymer solar cells were developed based on blend compositions (P1-P5):PC71BM. The values of J(sc), V-oc, and FF are in the range of 0.95-4.44 mA cm(-2), 0.67-0.69 V and 34.6-56.8%, and the power conversion efficiencies (PCE) are in the range of 0.22-1.74%, respectively, the highest value of 1.74% being for P3. Increase of the photovoltaic parameters was achieved with increasing iridium complex percentage in the polymers due to involvement of triplet effects. The improvement in the efficiency of the triplet-forming polymers P2 and P3 in comparison with P1 appears to be due to the formation of triplet excitons in comparison with singlet excitons in the polymer P1 which does not contain heavy metals. With further increase in the content of iridium complex fragments in the polymers, for example, up to 3 mol% for polymer P4, the efficiency falls to 1.23% and further decreased to 0.22% for P5.
New thienofluoroanthenes as building blocks for optoelectronic applications
(2015-03-01)
Keshtov, M. L.
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Godovsky, D. Yu.
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Kuklin, S. A.
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Zou, Y.
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Chen, F. Ch.
Novel regular D-A-conjugated polymers based on 2,6-bis(6-fluoro-2-hexyl-2H-benzotriazol-4-yl)-4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b\']dithiophene derivatives: Synthesis, optoelectronic, and electrochemical properties
(2016-09)
Keshtov, M. L.
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Kuklin, S. A.
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Ostapov, I. E.
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Chen, Fang-Chung
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Khokhlov, A. R.
Regioregular (P1) and random (P2) polymers were prepared by the reaction of equimolar amounts of dibromides M2 or M3 with bis(stannyl) monomer M1. The regioregularity of the conjugated chain in P1 was shown to affect considerably its optical properties. The HOMO/LUMO values and electrochemical band gap for polymers P1 or P2 found by cyclic voltammetry are-5.40/-3.40,-5.31/-3.33, and 2.00/1.96 eV, respectively. The LUMO levels for P1 and P2 are located higher than for PC71BM (-4.3 eV) by 0.84 and 0.97 eV, respectively. The low-lying HOMO levels of P1 and P2 are favorable for the high value of open-circuit voltage and make these polymers attractable candidates for polymer solar cells.
Polymer solar cells based low bandgap A1-D-A2-D terpolymer based on fluorinated thiadiazoloquinoxaline and benzothiadiazole acceptors with energy loss less than 0.5 eV
(2017-07-01)
Keshtov, M. L.
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Kuklin, S. A.
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Khokhlov, A. R.
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Osipov, S. N.
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Radychev, N. A.
We synthesized an ultra low bandgap terpolymer denoted as P containing fluorinated-fluorene attached thiadiazoloquinoxaline and benzothiadiazole acceptors and thiophene as donor in its backbone and investigated its optical and electrochemical properties. This terpolymer is used for as donor along with PC71BM as electron acceptor in solution processed polymer solar cells (PSCs). The P showed a shows strong absorption band from 650 nm to 1100 nm with an optical bandgap of 1.12 eV and highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of -5.25 eV and -3.87 eV, respectively. After the optimization of P to PC71BM weight ratio, the optimized weight ratio 1: 2 in chlorobenzene (CB) solution, the PSC showed overall power conversion efficiency of 4.10% (J(sc) of 10.96 mA/cm(2), V-oc of 0.68 V and FF of 0.55). After the solvent additive (3 v% DIO) followed by subsequent thermal annealing (SA-TA) the PCE has been increased up to 7.54% with Jsc of 16.12 mA/cm(2), Voc of 0.65 V and FF of 0.72. The increase in the PCE is related with the enhancement in the both Jsc and FF, attributed optimized nanoscale morphology of the active layer for both efficient exciton dissociation and charge transport towards the electrodes and balanced charge transport in the device, induced by the TSA treatment of the active layer. This is the highest PCE of PSCs with an energy loss about 0.47 eV with the low bandgap of 1.12 eV. (C) 2017 Elsevier B.V. All rights reserved.
Symmetrical and unsymmetrical triphenylamine based diketopyrrolopyrroles and their use as donors for solution processed bulk heterojunction organic solar cells
(2016-01-01)
Patil, Yuvraj
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Misra, Rajneesh
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Chen, F. C.
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Keshtov, M. L.
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Sharma, Ganesh D.
Two small molecules DPP3 (D-pi-A) and DPP4 (D-pi-A-pi-D) with triphenylamine (TPA) donors and diketopyrrolopyrrole (DPP) acceptors linked with ethyne linkers were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. Their photonic, electronic, thermal and computational properties were investigated. The red shift in the electronic absorption spectra of DPP4 as compared to DPP3 is related to extended conjugation and increased donor-acceptor interaction. We have used DPP3 and DPP4 as electron donors along with PC71BM as an electron acceptor for solution processed bulk heterojunction organic solar cells. The solar cells prepared from DPP3: PC71BM and DPP4: PC71BM (1 : 2) processed from chloroform (CF) exhibit a power conversion efficiency (PCE) of 2.23% (J(sc) = 6.74 mA cm(-2), V-oc = 0.92 V and FF = 0.36) and 3.05% (J(sc) = 8.26 mA cm(-2), V-oc = 0.88 V and FF = 0.42), respectively. The higher PCE of the device with DPP4 compared to DPP3 was demonstrated as to the higher hole mobility and broader IPCE spectra. The devices based on DPP3: PC71BM and DPP4: PC71BM processed with solvent additive (1 v% DIO, 1,8-diiodooctane) showed PCE values of 4.06% and 5.31%, respectively. The device optimization results from the improvement of the balanced charge transport and better nanoscale morphology induced by the solvent additive.
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.
Synthesis, characterization and photovoltaic properties of new iridium-containing conjugated polymers
(2018-01-01)
Keshtov, M. L.
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Kuklin, S. A.
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Nikolaev, A. Yu.
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Chen, Fang-Chung
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Xie, Zhi-yuan
Novel donor-acceptor (D-A) copolymers P1-P5 with iridium-complexed moieties in their side chains have been synthesized on the base of new iridium-containing monomer. These copolymers absorb visible light in broad spectral range up to 680 nm. Optical bandgaps of P1-P5 are in the range of 1.96 - 2.08 eV, respectively. HOMO and LUMO energy levels of the polymers P1-P5 were estimated from cyclic voltanunetry measurement indicates that these copolymers are suitable for electron donor along PC71BM as electron acceptor for the hulk heterojunction polymer solar cells. BHJ polymer solar cells were developed based on blend compositions (Pl-P5):PC7IBM. The values of Jsc, Voc, and FP are in the ranges of 0.95-4.44 mAfcm2; 0.67-0.69 V and 34.6-56.8%, power conversion efficiencies (PCE) are in the range of 0.22-1.74%, respectively, highest 1.74 for P3. Increasing of the photovoltaic parameters was achieved with increasing of iridium complexes percentage in the polymers due to involvement of triplet effects. The improvement in the efficiency of the triplet-forming polymers P2 and P3 in comparison with P1 appears to be due to the formation of triplet excitons in comparison with singlet excitons in the polymer P1 that does not contain heavy metals. With further increase in the content of iridium complex fragments in polymers, for example up to 3 mol% for polymer P4, the efficiency falls to 1.23% and further decreased up to 0.22 % for P5.
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.