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(1996)Journal ArticleThis paper presents an improved method for measuring the total lumped series resistance (Rs) of high-efficiency solar cells. Since this method greatly minimizes the influence of non-linear recombination processes on the measured Rs values, it is possible to determine Rs as a function of external current density over a wide range of illumination levels with a significantly improved level of accuracy. This paper furthermore explains how resistive losses in the emitter, the base, the metal/silicon contacts and the front metal grid can be separately determined by combining measurements and multidimensional numerical simulations. A novel combination of device simulation and circuit simulation is introduced in order to simulate complete 2 × 2 cm2 PERL (passivated emitter and rear locally-diffused) silicon solar cells. These computer simulations provide improved insight into the dynamics of resistive losses, and thus allow new strategies for the optimization of resistive losses to be developed. The predictions have been experimentally verified with PERL cells, whose resistive losses were reduced to approximately half of their previous values, contributing to a new efficiency world record (24.0%) for silicon solar cells under terrestrial illumination. The measurement techniques and optimization strategies presented here can be applied to most other types of solar cells, and to materials other than silicon.
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(1995)Journal ArticleThe `passivated emitter and rear locally diffused` (PERL) silicon solar cell structure presently demonstrates teh highes terrestrial performance of any silicon-based solar cell. This paper presents a detailed investigation of the limiting loss mechanisms in PERL cells exhibiting independently confirmend 1-sun efficiencies of up to 23.0%. Optical, resistice, and recombinative losses are all analyzed under the full range of solar cell operating conditions with the aid of two-dimensional (2D) device simulations. The analysis is based on measurements of the reflectance, quaantum efficiency, dark and illuminated current-voltage (I-V) characteristics, and properties of the Si-SiO2 interfaces employed on these cells for surface passivation. Through the use of the 2D simulations, particular attention has been paid to the magnitudes of the spatially resolved recombination losses in these cells. Itis shown that approximately 50% of the recombination losses at the 1-sun maximum power point occur in the base of th cells, followed by the recombination losses at the rear and front oxidised surfaces (25% and <25%, respectively). The relativerly low fill factors of PERL cells are princip[ally a result of resistive losses; however, the recombination behavior in the base and at the rear surfacealso contributes. This work predicts that the efficiency of 23% PERL cells could be increased by about 0.7% absolute if ohmic losses were eliminated, a further 1.1% absolute if there were no reflection losses at the nonmetallised front surface regions, about 2.0% by introducing ideal light trapping and eliminating shading losses due to the front metallisation, and by about 3.7% absolute if the device had no defect-related reconbination losses. New design rules for future efficiency improvements, ev
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Freezing-Induced Hydration Forces Between Phospatidylcholine Bilayers-The Effect of Osmotic Pressure(1997)Journal ArticleQuantitative nuclear magnetic resonance was used to measure the freezing behaviour of lamellar phases of phosphatidylcholine in water and in solutions of sorbitol. Both solute and solvent were deuterated in different series of experiments to allow the calculation of the partitioning of solute and solvent molecules between the lamellar phase and unfrozen bulk solution. Sorbitol, as well as water, was found to redistribute between these phases as a function of temperature. The results show a strong, repulsive, interlamellar force which decreases approximately exponentially with hydration. Compared to measurements on lipid/water systems and solute/water systems, the hydration of the lamellar phase containing solutes is slightly less than the sum of the hydrations of lipid and solute at any given chemical potential of water. For a lamellar phase with a given quantity of lipid, interlamellar sorbitol and water, reduction of chemical potential of water is greater than that due to lipid acting alone plus that due to solute acting alone.
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(1995)Journal Article
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(1996)Journal ArticleWe report the development of a novel and simple technique for fabricating polymer optical fibers of good optical quality for special device applications. This technique aims at polymer fibers doped with various functional organic materials. On the basis of the technique, step-index polymer optical fibers doped with laser dyes have been fabricated. High-gain and high-efficiency optical amplification has been achieved in a Rhodamine B-doped polymer fiber with a low pump power of less 1 kW and pulse width 5 ns. Because a high dye concentration is used, the optimal wavelength range of optical amplification in this fiber is significantly red-shifted toward the center of the communication window (at 650 nm wavelength) of methyl methacrylate-based polymer optical fiber. The shift is from the originally 560 and 590 nm to presently 610 to 640 nm. We also present experimental results that show good photostability of the Rhodamine B-doped polymer fiber, compared with those recently reported in the improved polymer material systems. From the experimental observation, we identified the thermally induced bleach of dye molecules as the major contributing factor to the lifetime of our material system
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(1996)Journal ArticleStep-index polymer optical fibre doped with Rhodamine B at 2500 ppm level is fabricated. Using the fibre, we have achieved high-gain and high-efficiency optical amplification with a tunable wavelength range from 610 nm to 640 nm, which is significantly red-shifted toward the centre of the communication window (at 650 nm wavelength) of methyl methacrylate-based polymer optical fibre.