A series of novel soluble conjugated copolymers consisting of coplanar donor (bithiophenevinyl)−acceptor (2-pyran-4-ylidenemalononitrile) (TVM)-based unit coupled to different electron-donating ability moieties were synthesized by Suzuki coupling polymerization. The structures of the copolymers were characterized, and their physical properties were investigated. High molecular weight (M n up to 43.8 kg/mol) and thermostable copolymers were obtained. The combination of TVM unit building block with gradually increased electron-donating ability moieties results in enhanced π−π stacking in solid state and intramolecular charge transfer (ICT) transition bands, which lead to an extension of their absorption spectral range. Cyclic voltammetry measurement displayed that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the copolymers can be fine-tuned. The resulting copolymers possessed relatively low HOMO energy levels promising good air stability and high open-circuit voltage (V oc) for photovoltaic application. Bulk heterojunction photovoltaic devices were fabricated by using the copolymers as donors and (6,6)-phenyl C61-butyric acid methyl ester (PCBM) as acceptor. It was found that the V oc reached 0.90 V, and the power conversion efficiencies (PCE) of the devices were measured between 0.04% and 0.99% under simulated AM 1.5 solar irradiation of 100 mW/cm2. The significant improvement of PCE indicates a novel concept for developing TVM-based donor−acceptor (D−A) conjugated copolymers with high photovoltaic performance by adjusting electron-donating ability and coplanarity.
A series of novel soluble polythiophene derivatives containing triphenylamine moiety were synthesized by Grignard metathesis (GRIM) method. The structures of the polymers were characterized and their physical properties were investigated. High molecular weight (Mn up to 25,800 g/mol) and thermostable polymers were obtained. The absorption spectra demonstrated that the absorption wavelength of the polymers could be tuned dramatically by introducing thiophene units in the main chain of the polymers. Photoluminescence spectra indicated that there was intramolecular energy transfer from the side chain to the main chain, and the maximum emission was red‐shifted gradually with the increase of thiophene units in the main chain. Cyclic voltammetry displayed that the polymers possessed relatively high oxidation potential, which promised good air stability and high open circuit voltage for photovoltaic cells application. Finally, bulk heterojunction photovoltaic devices were fabricated by using the polymers as donors and (6,6)‐phenyl C61‐butyric acid methyl ester (PCBM) as acceptor. The maximal open circuit voltage of the photovoltaic cells reached 0.71–0.87 V and the power conversion efficiencies of the devices were measured between 0.014% and 0.45% under white light at 100 mW/cm2. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3970–3984, 2008
Surface modifi cation of carbon materials plays an important role in tailoring carbon surface chemistry to specify their electrochemical performance. Here, a surface modifi cation strategy for graphene is proposed to produce LiFnanoparticle-modifi ed graphene as a high-rate, large-capacity pre-lithiated electrode for high-power and high-energy lithium ion batteries. The LiF nanoparticles covering the active sites of the graphene surface provide an extra Li source and act as an effective solid electrolyte interphase (SEI) inhibiter to suppress LiFP 6 electrolyte decomposition reactions, affect SEI components, and reduce their thickness. Consequently, the Li-ion diffusion is greatly sped up and the thermodynamic stability of the electrode is signifi cantly improved. This modifi ed graphene electrode shows excellent rate capability and improved fi rst-cycle coulombic effi ciency, cycling stability, and ultrahigh power and energy densities accessible during fast charge/discharge processes.research and development of improved electrode solutions for high-power LIBs.
Three novel conjugated copolymers containing alkoxylated 4,7-diphenyl-2,1,3-benzothiadiazole and dialkylfluorene or dialkyloxyphenylene or dialkylthiophene units were prepared by Horner polycondensation reactions. They are all soluble in common organic solvents such as chloroform, tetrahydrofuran, and chlorobenzene. The novel copolymers were characterized by NMR, GPC, and elemental analysis. Thermogravimetric analysis of the copolymers showed they have good thermal stability with the decomposition temperature higher than 350 °C. Cyclic voltammetric study shows that the HOMO energy levels of the three copolymers are deep-lying which implies that these copolymers have good stability in the air and the relatively low HOMO energy level assures a higher open circuit potential when they are used in photovoltaic cells. Bulk-heterojunction photovoltaic cells were fabricated with the copolymers as the donors and PCBM as the acceptor. The cells based on the three copolymers exhibited power conversion efficiencies of 0.65, 1.25, 1.62% with high open circuit potential of 0.76, 0.96, and 1.04 V under one sun of AM 1.5 solar simulator illumination (100 mW/cm 2 ).
A symmetrical D-π-A-π-D organic dye molecule 2-{2,6-bis-[2-(4-diphenylamino-phenyl)-vinyl]-pyran-4-ylidene}-malononitrile (DADP) has been introduced into solution-processable organic solar cells (S-P OSCs). Detailed investigations on the relationship between its molecular structure and thermal, photophysical, electrochemical properties and electronic structure are described. The optimized bulk heterojunction solar cell based on DADP as donor and PCBM as acceptor with the configuration of ITO/PEDOT/DADP:PCBM/ LiF/Al exhibits a Voc of 0.98 V, Isc of 4.16 mA/cm 2 , FF of 0.37, and power conversion efficiency (PCE) of 1.50% under the illumination of AM 1.5 simulated solar light (100 mW/cm 2 ). It was noted that the PCE of the device based on DADP is almost double that of the device based on TPA-DCM-TPA, an analogue of DADP, although there is only a small difference between their molecular structures; DADP has a shorter distance between the triphenylamine (TPA) group and the 2-pyran-4-ylidenemalonitrile (PM) group than TPA-DCM-TPA. This small structural difference results in a lower-lying highest occupied molecular orbital (HOMO) energy level and higher hole mobility in DADP, and ultimately leads to the increased PCEs of the DADPbased devices.
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