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Sharma G.D.,R and nter for Engineering and Science | Singh S.P.,Indian Institute of Chemical Technology | Roy M.S.,Defence Laboratory | Mikroyannidis J.A.,University of Patras
Organic Electronics: physics, materials, applications | Year: 2012

The improvement of near infrared wavelength sensitivity in the bulk heterojunction organic polymer solar cell based on poly (3-hexylthiophene) (P3HT) and PC 70BM, by the addition of soluble DPP-CN small molecule is reported. By incorporating DPP-CN, the photosensitivity in the longer wavelength region was improved and the power conversion efficiency (PCE) has been reached to 4.37% as compared to 3.23% for the device based on P3HT:PC 70BM blend. The increase in the PCE is attributed to the increase in light harvesting property of the blend and efficient dissociation of excitons into free charge carriers due to the increased number of D-A sites. The PCE has been further enhanced to 4.70%, when mixed solvent cast P3HT:DPP-CN:PC 70BM blend is used as photoactive layer. The optical absorption spectra of the blend showed that the blend film cast from mixed solvent broadened the absorption wavelength range. This occurred as result of a large red shift of P3HT absorption peak and same time a widening and small red shift of DPP-CN absorption peak in the blend film. The improved light harvesting property of thermally annealed film is considered to the factor responsible for the improvement in the PCE. © 2012 Elsevier B.V. All rights reserved. Source


Singh S.P.,Indian Institute of Chemical Technology | Kumar C.P.,Indian Institute of Chemical Technology | Sharma G.D.,R and nter for Engineering and Science | Kurchania R.,Maulana Azad National Institute of Technology | Roy M.S.,Defence Laboratory
Advanced Functional Materials | Year: 2012

A simple and effective modification of phenyl-C 70-butyric acid methyl ester (PC 70BM) is carried out in a single step after which the material is used as electron acceptor for bulk heterojunction polymer solar cells (PSCs). The modified PC 70BM, namely CN-PC 70BM, showed broader and stronger absorption in the visible region (350-550 nm) of the solar spectrum than PC 70BM because of the presence of a cyanovinylene 4-nitrophenyl segment. The lowest unoccupied molecular energy level (LUMO) of CN-PC 70BM is higher than that of PC 70BM by 0.15 eV. The PSC based on the blend (cast from tetrahydrofuran (THF) solution) consists of P3HT as the electron donor and CN-PC 70BM as the electron acceptor and shows a power conversion efficiency (PCE) of 4.88%, which is higher than that of devices based on PC 70BM as the electron acceptor (3.23%). The higher PCE of the solar cell based on P3HT:CN-PC 70BM is related to the increase in both the short circuit current (J sc) and the open circuit voltage (V oc). The increase in J sc is related to the stronger light absorption of CN-PC 70BM in the visible region of the solar spectrum as compared to that of PC 70BM. In other words, more excitons are generated in the bulk heterojunction (BHJ) active layer. On the other hand, the higher difference between the LUMO of CN-PC 70BM and the HOMO of P3HT causes an enhancement in the V oc. The addition of 2% (v/v) 1-chloronapthalene (CN) to the THF solvent during film deposition results in an overall improvement of the PCE up to 5.83%. This improvement in PCE can be attributed to the enhanced crystallinity of the blend (particularly of P3HT) and more balanced charge transport in the device. The photovoltaic properties of a bulk heterojunction based on poly(3- hexylthiophene) (P3HT):modified phenyl-C 70-butyric acid methyl ester (PC 70BM), a CN-PC 70BM blend, are studied. Polymer solar cells based on this blend demonstrate power conversion efficiencies of 5.8% with high open circuit voltages of 0.80 and short circuit current densities of 11.75 mA cm -2. These devices benefit from the high lowest unoccupied molecular orbital (LUMO) energy level of CN-PC 70BM and a more balanced charge transport. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Sharma G.D.,R and nter for Engineering and Science | Roy M.S.,Defence Laboratory | Singh S.P.,Indian Institute of Chemical Technology
Journal of Materials Chemistry | Year: 2012

We have used a stepwise approach for cosensitization of a thiocyanate-free Ru(ii) sensitizer with an organic dye (TDPP) for dye sensitized solar cells. The cosensitized SPS-01 + TDPP device showed enhanced V oc and J sc relative to the individual dye sensitized solar cells. Upon the optimization, the device made of SPS-01 + TDPP dye yielded J sc = 13.7 mA cm -2, V oc = 0.70 V, FF = 0.72 and power conversion efficiency (PCE) = 6.90%. This performance is superior to that of either individual DSSC made from SPS-01 (PCE = 5.47%) and TDPP (PCE = 4.82%), fabricated under the same conditions. This journal is © The Royal Society of Chemistry. Source


Sharma G.D.,Randnter for Science and Engineering | Roy M.S.,Defence Laboratory | Mikroyannidis J.A.,University of Patras | Justin Thomas K.R.,Indian Institute of Technology Roorkee
Organic Electronics: physics, materials, applications | Year: 2012

A symmetrical perylene bisimide derivative (PBI) with 2-(4-nitrophenyl) acrylonitrile groups at the 1,7 bay positions of perylene and solubilizing cyclohexyl units was synthesized and characterized. The absorption spectrum of PBI was broad with the most prominent peak at 655 nm and optical band gap of 1.72 eV. The electrochemical investigation indicates that PBI has a LUMO energy level of -3.9 eV which is similar to that of PCBM or PC70BM. Bulk heterojunction solar cell fabricated using a blend of poly(3-hexylthiophene) (P3HT) and PBI (1:1 w/w) as active layer cast from THF exhibited power conversion efficiency (PCE) at 1.56%. However, the device with P3HT:PBI blend deposited from mixed solvent (DIO/THF) improved the PCE to 2.78% which further increased to 3.17% on using the thermal annealed active layer. The improvement in the PCE is attributed to the enhanced crystallinity of the blend (particularly P3HT) and increase in hole mobility leading to balanced charge transport. © 2012 Elsevier B.V. All rights reserved. Source


Sharma G.D.,Randnter for Science and Engineering | Patel K.R.,Jai Narain Vyas University | Roy M.S.,Defence Laboratory | Misra R.,Indian Institute of Technology Indore
Organic Electronics: physics, materials, applications | Year: 2014

We report the photophysical, electrochemical and theoretical properties of two dyes with same acceptor, π-linker and anchoring acceptor unit and different TPA (D1) and pyran (D2) donor central unit. The change in the central unit resulted in corresponding different photophysical and electrochemical properties. The dye sensitized solar cell fabricated using dye D1 showed the higher incident photon to current efficiency of 54%, a short circuit current (Jsc) of 11.86 mA/cm2, an open circuit voltage of 0.64 V, and fill factor (FF) of 0.68, corresponding an overall power conversion efficiency of 5.16% which is higher than that for D2 based DSSCs (4.42%). The difference in the PCE of DSSCs based on D1 and D2 is partly, due to the smaller amount of dye loading, higher dark current and charge recombination rate of D1 based DSSC. The electrochemical spectra of DSSCs demonstrated longer electron life time and charge recombination resistance and small charge transport resistance for D1 sensitized DSSC, results the higher PCE. © 2014 Elsevier B.V. All rights reserved. Source

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