Dual electron donor/electron acceptor character of a conjugated polymer in efficient photovoltaic diodes (original) (raw)
2007, Applied Physics Letters
https://doi.org/10.1063/1.2738197
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Abstract
Poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3benzothiadiazole]-2 ,2 -diyl) (F8TBT) was developed by Cambridge Display Technology Ltd. The molecular weight of the sample used was M p = 432,000 g/mol. Poly(3hexylthiophene) (P3HT) was supplied by Merck KGaA with molecular weight M w~ 25,000 g/mol and regioregularity of ~ 94 %. (6,6)-phenyl C 61 -butyric acid methyl ester (PCBM) was supplied by Nano C, Inc.
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Journal of Polymer Science Part A: Polymer Chemistry, 2011
Three novel low-bandgap copolymers containing alkylated 4,7-dithien-2-yl-2,1,3-benzothiadiazole (HBT) and different electron-rich functional groups (dialkylfluorene (PFV-HBT), dialkyloxyphenylene (PPV-HBT) and dialkylthiophene (PTV-HBT)) were prepared by Horner polycondensation reactions and characterized by 1 H NMR, gel permeation chromatography, and elemental analysis. The alkyl side chain brings these polymeric materials good solubility in common organic solvents, which is critical for the manufacture of solar cells in a cost-effective manner. The copolymers exhibit low optical bandgap from 1.48 to 1.83 eV. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the copolymers were measured by cyclic voltammetry. Theoreti-cal calculations revealed that the variation laws of HOMO and the LUMO energy levels are well consistent with cyclic voltammetry measurement. The bulk heterojunction photovoltaic devices with the structure of ITO/PEDOT-PSS/polymer:PCBM/LiF/Al were fabricated by using the three copolymers as the donor and (6,6)-phenyl-C 61 -butyric acid methyl ester (PCBM) as the acceptor in the active layer. The device based on PTV-HBT:PCBM (1:4 w/w) achieved a power conversion efficiency of 1.05% under the illumination of AM 1.5, 100 mW/cm 2 . V
Organic Electronics, 2017
Direct arylation polymerization (DAP) is emerging as a promising green, cheap, simple, and efficient environment friendly method for synthesizing conjugated polymers without involving any organometallic reagent. We report fluorene based novel cross-conjugated alternate and random copolymers for polymer solar cells (PSCs), which were synthesized by DAP and/or Yamamoto polymerization under appropriate reaction conditions to obtain high molecular weight. These cross-conjugated polymers possess absorption maxima in the range of 490e520 nm and have narrow band gap (1.7e2.05 eV) which is suitable for bulk heterojuntion (BHJ) type organic solar cells. Among the synthesized polymers, the highest number average molecular weight (M n) i.e. 43.1 kg mol À1 was obtained for polymer P2b (poly((9H-fluoren-9-ylidene)methylene)bis((2-ethylhexyl)sulfane)-alt-4,7-di(thiophen-2-yl)benzo[c] [1,2,5]thiadiazole)), and so good polymeric films were formed for P2b. Thus, BHJ films were prepared for P2b for device performance studies and the morphology of these films was studied by atomic force microscopy (AFM). Polymer P2b was blended with the fullerene derivative [6,6]-phenyl C 71 butyric acid methyl ester (PC 71 BM) in different ratios and under the illumination of solar simulator with Air Mass global (AM 1.5G) irradiated at 100 mW cm À2. Power conversion efficiency (PCE) of 1.4% has been achieved for BHJs in ratio of 1:2 of P2b: PC 71 BM in simply processed devices. This result indicates that crossconjugated polymers can be tapped as potential donors for BHJs as the PCE obtained is the highest among this type of cross-conjugated polymers.
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Journal of Polymer Science Part A: Polymer Chemistry, 2011
A strategy of the fine-tuning of the degree of intrachain charge transfer and aromaticity of polymer backbone was adopted to design and synthesize new polymers applicable in photovoltaics. Three conjugated polymers P1, P2, and P3 were synthesized by alternating the electron-donating dithieno[3,2-b:2 0 3 0 -d]pyrrole (D) and three different electronaccepting (A) segments (P1: N-(2-ethylhexyl)phthalimide; P2: 1,4-diketo-3,6-diphenylpyrrolo[3,4-c]pyrrole; and P3: thiophene-3-hexyl formate) in the polymer main chain. Among the three polymers, P2 possessed the broadest absorption band ranging from 300 to 760 nm, the lowest bandgap (1.63 eV), and enough low HOMO energy level (À5.27 eV) because of the strong intrachain charge transfer from D to A units and the appropriate extent of quinoid state in the main chain of P2, which was convinced by the theoretical simulation of molecular geometry and front orbits. Photovoltaic study of solar cells based on the blends of P1-P3 and [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) demonstrated that P2:PCBM exhibited the best performance: a power conversion efficiency of 1.22% with a high open-circuit voltage (V OC ) of 0.70 V and a large short-circuit current (I SC ) of 5.02 mA/cm 2 were achieved.
Applied Physics Letters, 2007
The properties of organic photovoltaic devices (OPVs) with poly(3,4-ethylene dioxythiophene) : poly(styrene-sulfonate) buffer layer modified by doping glycerol with different concentration have been investigated. The power conversion efficiency (PCE) of the device has been improved from 3.37% to 4.32% under AM 1.5 G (90 mW/cm 2 illumination) after the buffer layer was modified. The short-circuit current density also 24% increased with the modification. Surprisingly, as the doping concentration of glycerol was more than 30 mg/ml, PCE of the OPVs no longer increased even though the conductivity of buffer layer continually increased with doping concentration of glycerol. We particularly analyzed the effect of glycerol-modified buffer layer on performance of polymer photovoltaic devices by the contact angle and atomic force microscopy measurements, and the influence of surface morphology of buffer layer was also discussed.
Journal of Photochemistry and Photobiology A: Chemistry, 2013
After the discovery of photoinduced charge transfer in conjugated polymers, organic photovoltaic solar cells have been extensively studied due to many advantages that include flexibility and low-cost. In this context, we have synthesized a new class of conjugated polymer, poly(2-(4-{1-cyano-2-[5-(3-thiophen-2-yl-benzo[c]thiophen-1-yl)-thiophen-2-yl]-vinyl}-2,5bis-hexyloxy-phenyl)-but-2-enenitrile) (CN-PTBTBPB) for the fabrication of low cost organic solar cells. The electron donor properties of CN-PTBTBPB polymer was incorporated by means of facile Knoevenagel condensation process followed by a chemical oxidative polymerization method using oligo-5-(1-benzo[c]thiophen-3-yl)thiophene-2-carboxaldehyde with 1,4-bis(cyanomethyl) benzene linkages. The polymer was characterized by 1 H NMR and GPC techniques. The electronic and structural properties of the polymer were evaluated by UV-vis spectroscopy, fluorescence spectroscopy, and thermo gravimetric analysis. In order to establish the energy diagram of the prepared polymer, the energy gap between HOMO-LUMO was evaluated using electrochemical measurements and Density Functional Theory (DFT). The resulting CN-PTBTBPB polymer was experimentally found to possess low-lying HOMO (about −5.84 eV) and high-lying LUMO (about −3.87 eV) energy levels. This polymer exhibited a relatively wide optical band gap of ∼1.95 eV in the solid state. Using this polymer, organic photovoltaic cells were fabricated in open air of type ITO/PEDOT:PSS/CN-PTBTBPB:PCBM/Al showed promising photovoltaic properties.
The Journal of Physical Chemistry C, 2011
became attractive due to their ease of processing, formation of large areas, flexibility, and low cost. 1,2 To this end, the development of polymer solar cells has received much attention from both academic and industrial laboratories. In the past two years, great progress has been made in bulk-heterojunction (BHJ) PSCs, 3À5 but power conversion efficiency (PCE) is still a big challenge toward commercialization. To improve the PCE, it is very important to develop p-type conjugated polymers with low bandgap, high hole mobility, and deep lying HOMO energy level.
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