We present a general framework for the design of thin-film photovoltaics based on a partiallydisordered photonic crystal that has both enhanced absorption for light trapping and reduced sensitivity to the angle and polarization of incident radiation. The absorption characteristics of different lattice structures are investigated as an initial periodic structure is gradually perturbed. We find that an optimal amount of disorder controllably introduced into a multi-lattice photonic crystal causes the characteristic narrow-band, resonant peaks to be broadened resulting in a device with enhanced and robust performance ideal for typical operating conditions of photovoltaic applications.
We investigate the photoluminescence (PL) properties of a thick InGaN single quantum well (SQW) in which an AlGaN δ layer is embedded. The δ layer offers an extra degree of freedom which may be employed to tune the emission wavelength. One of the most salient features of such a QW structure is that the long-wavelength tuning is feasible with lower indium composition. The δ layer also increases the wave function overlap between holes and electrons, shortening the PL lifetime. All the measurement results are consistent with the numerical predictions. The QW structure could be of great importance in the design of long-wavelength lasers.
The water‐soluble monomers, 1‐methyl‐4‐vinylimidazole, 1‐methyl‐5‐vinylimidazole, 1‐ethyl‐5‐vinylimidazole, and 1‐propyl‐5‐vinylimidazole have been synthesized, polymerized, and copolymerized with 4(5)‐vinylimidazole. The copolymers were characterized by 14C‐labeling, NMR, pKa determination and viscosity measurements. The monomer reactivity ratios determined by 14C counting are r1 = 1.04; r2 = 0.94 [M1 = 4(5)‐vinylimidazole, M2 = 1‐methyl‐4‐vinylimidazole] and r1 = 1.01; r2 = 0.86 [M1 = 4(5)‐vinylimidazole, M2 = 1‐methyl‐5‐vinylimidazole]. The esterolytic activity of the copolymers for the hydrolysis of p‐nitrophenyl acetate (PNPA) at pH 7–8 in 28.5% ethanol–water was higher than that of the mixtures of homopolymers. At pH 5–6 the esterolytic activities of the copolymers and the mixtures were similar. The most efficient esterolytic activity for PNPA hydrolysis at pH 7.11 in 28.5% ethanol–water occurred for copolymers containing 75 mole % 4(5)‐vinylimidazole and for copolymers containing 1‐methyl‐4‐vinylimidazole rather than 1‐methyl‐5‐vinylimidazole.
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