Browsing by Author "Koukaras, E. N."

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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.
;
Kuklin, S. A.
;
Khokhlov, A. R.
;
Osipov, S. N.
;
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.
Synthesis of alternating D-A1-D-A2 terpolymers comprising two electron-deficient moieties, quinoxaline and benzothiadiazole units for photovoltaic applications
(2016)
Keshtov, M. L.
;
Khokhlov, A. R.
;
Kuklin, S. A.
;
Chen, F. C.
;
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.