Engineering

Publication Search Results

Now showing 1 - 10 of 37
  • (1995) Altermatt, Peter; Heiser, Gernot; Zhao, Jun; Wang, Alan; Wenham, Stuart; Green, Martin
    Conference Paper

  • (1995) Heiser, Gernot; Altermatt, Peter; Williams, Angela-Margaret; Sproul, Alistair; Green, Martin
    Conference Paper
    This paper describes the use of three-dimensional (3D) device modelling for the optimisation of the rear contact geometry of high-efficiency silicon solar cells. We describe the techniques and models used as well as their limitations. Our approach is contrasted with previously published 3D studies of high-efficiency silicon solar cells. Results show that the optimum spacing is about 2/3 of that predicted by 2D simulations, and exhibits a much stronger dependence on contact spacing. The optimal value found is about 60% of that of the present UNSW PERL cells, however, the possible efficiency gain is only about 0.1% absolute.

  • (1995) Heiser, Gernot; Altermatt, Pietro; Litsios, J
    Conference Paper
    This paper reports on simulation techniques developed for the modelling and optimisation of complete, 2x cm^2, high-efficiency silicon solar cells. We use three-dimensional (3D) device simulation to extract a J-V curve of an interior section of a cell. 2D simulations of the cell perimeter are then used to correct the J-V curves for the loss of carriers across the cell boundary. The resulting characteristics are input to a circuit simulation which connects the various cell sections into a model of a full cell. The J-V curve which results from that simulation can be directly compared to measured data. We find excellent agreement between simulation and measurement.

  • (1995) Heiser, Gernot; Aberle, Armin; Wenham, Stuart; Green, Martin
    Journal Article
    This paper reports on the first use of two-dimensional (2D) device simulation for optimising the front-finger spacing of one-sun high-efficiency silicon solar cells of emph{practical} dimensions. We examine the 2D current flow patterns in these devices under various illumination conditions, resulting in improved insight into the operating conditions of the cells. Results for the optimal spacing of the front metal fingers are presented and compared to predictions obtained from 1D simulations. We also address difficulties facing the numerical modelling of high-efficiency silicon solar cells.

  • (1995) Robinson, Steven J.; Wenham, Stuart; Altermatt, Peter; Aberle, Armin; Heiser, Gernot; Green, Martin
    Journal Article
    Sholders have been observed in the measured semilogarithmic current-voltage (I-V) characteristics of high-efficiency passivated emitter and rear locally diffused silicon (Si) solar cells. An improved understanding is giben of the mechanism proposed to cause these nonideal I-V curves. It is shown that this mechanism is due to the electrostatic behavior of free carriers at the Si/SiO2 interface of oxidised Si devices in which the Si adjacent to the oxide is depleted (or in some cases, inverted) at equilibrium, and results in saturation of the surface recombination rate. Two-dimensional numerical computer simulations are used to investigate this mechanism and its effect on cell performance. In addition, the simu;ations provide a means to estimating the etent do which lateral conduction in the rear surface channel also contributes ot the observed recombination saturation in these cells. It is shiown that ohmic limitation of lateral conduction occurs, however, the lateral current flows are negligible in comparison to the recombination currents due to the former mechanism.

  • (1995) Aberle, Armin; Altermatt, Peter; Heiser, Gernot; Robinson, Steven J.; Wang, Alan; Zhao, Jun; Krumbein, U; Green, Martin
    Journal Article
    The `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

  • (1995) Helmore, Phillip
    Conference Paper
    Many methods for predicting the resistance of various types of marine craft are now available in the literature. Some methods are more reliable than others, and knowing which are the best can be important. At UNSW we have begun a long-term program of implementing the various methods for student use, and evaluating them by comparisons with available data. The prediction methods cover displacement, pre-planing and planing hulls, and catamarans. This paper looks at some of the methods which have been programmed and some which have not, their limitations, and some experiences of the use of those which have been programmed. The opportunity is also taken to correct typographical errata in some of the original papers which otherwise limits the use of the methods.

  • (1995) Mubaraki, Brian; Bandyopadhyay, Srikanta; Fowle, R; Mathew, Philip; Heath, P
    Journal Article

  • (1995) Zhao, Yong; Chen, B; Sorrell, Charles; He, Ying; Zuge, X; Chen, Zhixin
    Journal Article
    The scaling behaviour of vortex-glass superconductivity is studied, by measuring the resistive transition as well as the I-V curve under a variety of magnetic fields, in a series of V doped YBa2Cu307_y samples with different grain sizes. The equilibrium phase boundary line between the normal and superconducting phases in the H-T plane obtained by fitting the resistive transition is consistent with that obtained by the I-V curve measurements. As the magnetic field is lower than a certain value, Hs, the scaling exponents are magnetic-field independent, but at H = H s, they begin to increase with the magnetic field and gradually get saturation. The switch field, Hs, decreases with decreasing the grain size in the samples. The results show that the magnetic-field-dependent scaling behaviour of the I-V curve observed in weak-link containing systems originates from the transition of a "weak" vortex-glass state to a "strong" vortex-glass state.

  • (1995) Han, Shaowei; Gu, Genda; Zhao, Yong; Russell, Graeme; Koshizuka, N
    Journal Article
    Two types of Bi-2212 single crystals, one type having a low T c and the other having a high T¢ were annealed in air at different temperatures over the range 450°C to 750°C followed by furnace cooling. The transition temperature of the crystals with low T c (~ 56 K) increased with increase of annealing temperature, while the crystals with high Tc (~ 91 K) had just the opposite behaviour under the same annealing conditions. It is indicated that the quality of as-grown crystal has a significant effect on the superconducting properties of the annealed crystal. The c-axis values for both types of crystals decreased with increase of annealing temperature. According to the relationship between c-axis values and the oxygen content, our results confirmed the existence of a dome-shaped curve of T¢ with carrier concentration in Bi-2212 single crystal similar to that in Bi-2212 compound reported previously by Groen and de Leeuw [Physica C 159 (1989) 417]. By studying the increase of annealing time at a fixed temperature of 650°C, T¢ and ATe were found to change very little for both types of crystals. Thus, T c and AT~ were more sensitive to annealing temperature than to annealing time. XRD, SEM and EDS revealed that a small quantity of powder phase appeared after annealing at temperatures above 500°C for both types of crystals. This powder phase had the Bi-2212 composition, which indicated that the integrity of the Bi-2212 single crystals was significantly degraded by the annealing process.