Bandgap engineering of indenofluorene‐based conjugated copolymers with pendant donor‐π‐acceptor chromophores for photovoltaic applications

Three narrow‐band‐gap conjugated copolymers based on indenofluorene and triphenylamine with pendant donor‐π‐acceptor chromophores were successfully synthesized by post‐functionalization approach. All the polymers have good solubility in common solvents and excellent thermal stability. The photophysical properties, energy levels and band gaps of the polymers were well manipulated by introducing different acceptor groups onto the end of their conjugated side chains. By using different acceptor groups, the band gaps of the polymers were narrowed from 1.86 to 1.53 eV by lowering their lowest unoccupied molecular orbital levels, whereas their relatively deep highest occupied molecular orbital levels of approximately ?5.35 eV were maintained. Bulk‐heterojunction solar cells with these polymers as electron donors and (6,6)‐phenyl‐C₇₁‐butyric acid methyl ester as acceptor showed power conversion efficiencies as high as 3.1% and high open circuit voltages more than 0.88 eV. The relationships between the performance and film morphology, energy levels, charge mobilities were discussed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Low band gap copolymers consisting of porphyrins,thiophenes, and 2,1,3‐benzothiadiazole moieties for bulk heterojunction solar cells

Two novel low band gap conjugated copolymers containing porphyrins, thiophenes, and 2,1,3‐benzothiadiazole ( BTZ ) moieties were synthesized and applied in bulk heterojunction solar cells. The thermal, optical, electrochemical, and photovoltaic properties of the two copolymers were examined to investigate the effect of the introduction of BTZ moiety in the backbone of the porphyrin polymers. The copolymers exhibited good thermal stability and film‐forming ability. The absorption spectra indicated that the BTZ moiety has significant influence on the UV–visible region spectra of the copolymers: with increasing the molar amount of BTZ moieties in conjugated main chain, the absorption in the range of 450–700 nm is largely broadened and red‐shifted compared to the similar polymers without BTZ moiety, and the optical band gaps of copolymers were narrowed to ～1.50 eV. The photoluminescence spectra showed that there is effective charge transfer in the whole conjugated main chain. Cyclic voltammetry displayed that the band gaps were reduced effectively by the introduction of the BTZ moieties. The bulk heterojunction solar cells were fabricated based on the blend of the copolymers and [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) in a 1:2 weight ratio. The maximum power conversion efficiency of 0.91% was obtained by using P2 as the electron donor under the illumination of AM 1.5, 100 mW/cm². © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and photovoltaic behaviors of narrow‐band‐gap π‐conjugated polymers composed of dialkoxybenzodithiophene‐ and thiophene‐based fused aromatic rings

π‐Conjugated polymers, PBDT‐CNETT and PBDT‐CNECPDT , were prepared by the Stille cross‐coupling polymerization. Optical and thermal properties of the obtained polymers were investigated by UV–vis spectroscopy and thermogravimetric analysis. PBDT‐CNETT and PBDT‐CNECPDT exhibited very narrow band gaps of 1.39 and 1.13 eV, respectively. Highest occupied molecular orbital energy levels estimated by surface analyzer were ?5.17 and ?5.11 eV for PBDT‐CNETT and PBDT‐CNECPDT , respectively. The solar cells based on these polymers were evaluated with the cell configuration of ITO/PEDOT‐PSS/polymer:PC₆₁BH/LiF/Al. The power conversion efficiencies of the solar cells were estimated to be 1.57 and 0.16% for PBDT‐CNETT and PBDT‐CNECPDT , respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

光子晶体几何结构设计对LED出光效率影响的研究

利用禁带理论、等效介质理论分析了增透机理,研究了一种参数设计方法.采用FDTD方法计算了表面覆盖ITO层的六角排列圆形光子晶体出光效率.计算该结构参数的光子晶体的LED出光效率,结果表明加入ITO层的光子晶体能提高GaN基蓝光LED出光效率2倍,该参数设计思路也为光子晶体设计提供了参考依据.     

Computational study of the fluorination effect on nitrogen–boron bond

The Lewis acid‐base H_3?nF_nN–BF_mH_3?m (n = 0–3; m = 0–3) system was examined using the density functional theory calculations. The N? B bond strength can be adjusted stepwise by increasing the number of substituted fluorine atoms. The main finding of this work is the bond distances of the complexes do not correlate directly with the bond strengths. Some rationalization of this interesting observation was provided by the fluorine substitution effect on the HOMO‐LUMO gap, hybridization of bonding orbitals and electrostatic interaction. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Homogenization of periodic linear degenerate PDEs

It is well known under the name of ‘periodic homogenization’ that, under a centering condition of the drift, a periodic diffusion process on Rd converges, under diffusive rescaling, to a d-dimensional Brownian motion. Existing proofs of this result all rely on uniform ellipticity or hypoellipticity assumptions on the diffusion. In this paper, we considerably weaken these assumptions in order to allow for the diffusion coefficient to even vanish on an open set. As a consequence, it is no longer the case that the effective diffusivity matrix is necessarily non-degenerate. It turns out that, provided that some very weak regularity conditions are met, the range of the effective diffusivity matrix can be read off the shape of the support of the invariant measure for the periodic diffusion. In particular, this gives some easily verifiable conditions for the effective diffusivity matrix to be of full rank. We also discuss the application of our results to the homogenization of a class of elliptic and parabolic PDEs.     

Optical properties of CdSxTe1−x polycrystalline thin films

Thin films of CdS_xTe_1−x (0≤x≤ 1) have been prepared by vacuum evaporation from solid solutions. Rutherford backscattering spectrometry has been used to determine the thickness of the films, which is in the range 8–50 nm, and x-ray diffraction analysis has been used to determine the phase. The refractive index and extinction coefficient of the films has been calculated from reflectance and transmittance measurements for the wavelength region 250–3200 nm. Polynomial functions are given for each sample, which describe the variation in refractive index and extinction coefficient over the entire wavelength range. Least squares fitting to the absorption spectra revealed that the films all have a direct band gap, although photon energies required for indirect transitions have also been found. CdS_0.8Te_0.2 is found to have the lowest absorption coefficient at energies greater than 2.1 eV.     

Sensitivity and crosstalk study of the zero gap microlens used in 3.2 μm active pixel image sensors

The microlens has been widely applied to improve the sensitivity and to decrease the spatial crosstalk of image sensors. In order to further decrease the pixel size while improve the image quality, the zero gap microlens has been proposed to make high performance image sensors. In this paper, both the traditional microlens and zero gap microlens are fabricated using TOWER and TOPPAN processes. And their performances are compared and evaluated. The results show that the least sensitivity of the zero gap microlens has been significantly improved by more than 45.8% compared to that of the traditional microlens. The use of the zero gap microlens results in an obvious decrease of the crosstalk among blue, green and red lights. For example, the crosstalk of blue light in red light under the green irradiation has been decreases about 1.33%, and the crosstalk of red light in blue light under the blue irradiation has showed about 2.429 times decrease. Overall, the output colour image of the zero gap microlens is brighter and clearer than that of the traditional microlens. Image quality has been significantly improved due to the use of the zero gap microlens.     

Gâteaux differentiability of the dual gap function of a variational inequality

In terms of the mapping involved in a variational inequality, we characterize the Gâteaux differentiability of the dual gap function G and present several sufficient conditions for its directional derivative expression, including one weaker than that of Danskin [J.M. Danskin, The theory of max–min, with applications, SIAM Journal on Applied Mathematics 14 (1966) 641–664]. When the solution set of a variational inequality problem is contained in that of its dual problem, the Gâteaux differentiability of G on the latter turns out to be equivalent to the conditions appearing in the authors’ recent results about the weakly sharp solutions of the variational inequality problem.     

Structural and optical properties of pulsed laser deposited SrBi2Nb2O9 thin films

SrBi₂Nb₂O₉ (SBN) thin films were prepared on fused quartz substrates at room temperature by pulsed laser deposition. The influence of deposition parameters such as target-to-substrate distance, oxygen pressure and annealing temperature on film crystallization behavior was investigated by X-ray diffraction. Results indicated that the films grown at the optimum processing conditions have polycrystalline structure with a single layered perovskite phase. The optical transmittance of the films prepared at various oxygen pressures was measured in the wavelength range 200–900 nm using UV–vis spectrophotometer. The results showed that there is a red shift in the optical absorption edge with a rise in the oxygen pressure. Refractive index as a function of wavelength and optical band gap of the films were determined from the optical transmittance spectra. The results indicated that the refractive index increases with increasing oxygen pressure at the same incident light wavelength, while the band gap reduces from 4.13 to 3.88 eV. It may be attributed to an increase in packing density and grain size, and decrease in oxygen defects.