AlxGa1-xAs/GaAs太阳电池MgF2/ZnS双层减反射膜的研究

介绍了在AlxGa1-xAs/GaAs太阳电池上制备MgF2/ZnS双层减反射膜的研究工作,引入了有效反射率R,并通过使Re极小来实现减反射膜的优化设计,考虑了MgF2/ZnS双层减反射膜与窗口层的耦合,实验上获得了良好的减反射膜,提高了AlxGa1-xAs/GaAs太阳电池的短路电流和效率,表明用Re极小化来设计减反射膜是合理的。     

First-principles study the structural,electronic, vibrational and thermodynamic properties of Zr1−xHfxCoH3

The structural, electronic, vibrational and thermodynamic properties of Zr_1?xHf_xCoH₃ (x = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) are investigated using first principles approach based on the virtual crystal approximation (VCA). The results indicate the series Zr_1?xHf_xCoH₃ have the similar physical properties. When Hf concentration increases gradually, the lattice parameter reduces and the thermodynamic stability first decreases and then increases, respectively. The calculated results of charge distributions and electron localization function (ELF) suggest that the interactions of HCo and HZr_1?xHf_x are primarily metallic with a small covalent component. The band structure and the corresponding density of states (DOS) around the Fermi level (E_f) indicate the metallicity enhances and the electrical conductivity is better with increasing Hf content. The phonon density of states imply that with the increase of Hf content, the covalent interactions between H(4c₂) and Zr_1?xHf_x are weakened, while the covalent interactions between H(8f₁) and Zr_1?xHf_x basically remained unchanged (H(4c₂) and H(8f₁) represent the hydrogen atoms occupying 4c₂ and 8f₁ site, respectively), which is consistent with the results of charge density. Finally, the thermodynamic properties are obtained and discussed on the base of the obtained vibrational properties.     

Over 27% efficiency GaAs/InGaAs mechanically stacked solar cell

We have applied an InGaAs solar cell (band GAP = 0.75 eV) to the bottom cell of the super-high-efficiency tandem solar cell aiming an over 35% conversion efficiency. The InGaAs cell which is lattice-matched to the InP substrate showed the efficiency of 5.5% under the GaAs substrate with low carrier concentration. Combining with the GaAs cell by means of a mechanically stacking technique, we obtained an efficiency of 28.8% at air mass (AM) 1.5, 1-sun. This result suggests the possibility of the cells with the efficiency of over 35% with combining a GalnP/GaAs monolithic tandem cell and the InGaAs cell (or InGaAsP cell).     

Radiation-resistant solar cells for space use

This paper reviews the present status of radiation-resistant solar cells made with Si, GaAs, InP and InGaP/GaAs for space use. At first, properties of radiation-induced defects in semiconductor materials and solar cells are described based on an anomalous degradation of Si space solar cells under high-energy, high-fluence electron and proton irradiations. Advantages of direct bandgap materials as radiation-resistant space cells are presented. Unique properties of InP as radiation-resistant cells have also been found. A world-record efficiency of 26.9% (AM0) has been obtained for an InGaP/GaAs tandem solar cell. Radiation-resistance of the InGaP/GaAs tandem cells is described.     

Light-splitting photovoltaic system utilizing two dual-junction solar cells

There are many difficulties limiting the further development of monolithic multi-junction solar cells, such as the growth of lattice-mismatched material and the current matching constraint. As an alternative approach, the light-splitting photovoltaic system is investigated intensively in different aspects, including the energy loss mechanism and the choice of energy bandgaps of solar cells. Based on the investigation, a two-dual junction system has been implemented employing lattice-matched GaInP/GaAs and InGaAsP/InGaAs cells grown epitaxially on GaAs and InP substrates, respectively.     

Temperature dependence of photocurrent components on enhanced performance GaAs/AlGaAs multiple quantum well solar cells

The performance of Al_0.36Ga_0.64As p/i/n solar cells with multiple quantum wells (MQW) of GaAs/Al_0.36Ga_0.64As in the i-region has been investigated at various temperatures, ranging from −10°C to 100°C, and compared with that of conventional solar cells composed of either the quantum well material (GaAs) or the barrier material (Al_0.36Ga_0.64As) alone. The dark currents of the MQW cells were found to lie between those of the conventional cells. The increase of dark current with temperature was accompanied by a slight decrease of the diode ideality factor. A linear dependence of open-circuit voltage (V_oc) on temperature was observed for all cells when illuminated with a 100W halogen lamp. V_oc for the MQW cells was found to be independent of the number of wells, lying between the V_oc's for the two conventional cells. The MQW cells exhibited performance improvement with temperature when compared to the conventional cells and there was a significant enhancement in the short-circuit current with temperature of those MQW cells that exhibited poorer performance at lower temperatures. Theoretical calculations have quantified the contribution of the tunneling current component to the total observed photocurrent at the various temperatures examined. It was found that tunneling currents are present at all temperatures and can be the dominant component in MQW cells of thinner wells at low temperatures. These results suggest that GaAs/Al_0.36Ga_0.64As MQW structures, of good-quality material, when processed as conventional solar cells with antireflective coatings should deliver more output power under intense illumination than conventional solar cells composed of the quantum well material alone.     

GaAs/Ge solar cell AC parameters under illumination

The ac parameters of GaAs/Ge solar cell were measured under illumination at different cell temperatures using impedance spectroscopy technique. They are compared with the dark measurements. It is found that the cell capacitance is higher and cell resistance is lower under illumination than in dark for all cell terminal voltages. The cell capacitances at the corresponding maximum power point voltage (terminal) do not vary with temperature where as the cell resistance decreases. The cell capacitance under illumination is estimated from the dark cell capacitance and it is in good agreement with the measured illumination data.     

Synthesis of nanostructured Al-doped zinc oxide films on Si for solar cells applications

Al-doped ZnO thin films have been prepared by a novel successive chemical solution deposition technique. The variation in morphological, structural, electrical, and optical properties of nanostructured films with doping concentration is investigated in details. It was demonstrated that rapid photothermal processing (RPP) improves the quality of nanostructured ZnO films according to the enhancement of resonant Raman scattering efficiency, and the suppression of the visible luminescence with the increase of RPP temperature. It was found from the I-V characteristics of ZnO/Si heterojunction that the average short-circuit current density is about 8 mA/cm². For 1%Al-doped ZnO/SiO₂/Si structure, the short-circuit current density is about 28 mA/cm². The improvement shown in the characteristics may be assigned partially to the reduction of the defect density in the nanostructured Al-doped ZnO films after RPP. The correlations between the composition, microstructure of the films and the properties of the solar cell structures are discussed. The successive chemically deposited Al-doped ZnO thin film offers wider applications of low-cost solar cells in heterojunction structures.     

5–20 MeV proton irradiation effects on GaAs/Ge solar cells for space use

This paper reports the high-energy proton irradiation effects on GaAs/Ge space solar cells. The solar cells were irradiated by protons with energy of 5–20 MeV at a fluence ranging from 1×10⁹ to 7×10¹³ cm⁻², and then their electric parameters were measured at AM0. It was shown that the I_sc, V_oc and P_max degrade as the fluence increases, respectively, but the degradation rates of I_sc, V_oc and P_max decrease as the proton energy increases, and the degradation is relative to proton irradiation-induced defect Ec−0.41 eV in irradiated GaAs/Ge cells.     

Optimal growth procedure of GaInP/GaAs heterostructure for high-efficiency solar cells

We have developed an optimal growth procedure for gas-source MBE production of a GaInP/GaAs heterointerface. The interface quality is crucial to obtaining high-performance GaAs solar cells with a GaInP barrier layer because minority carrier lifetime depends strongly on the interface structure. In situ Reflective High-Energy Electron Diffraction (RHEED) observation during the growth across the GaInP/GaAs heterointerface revealed that the phosphorus atoms are replaced by arsenic atoms in the near-interface region of the GaInP layer, and a transient layer acting as a carrier trap is formed. Introduction of a GaP layer into the interface was found to be effective in suppressing carrier loss. From Composition Analysis by Thickness Fringe-Transmission Electron Microscopy (CAT-TEM) images, it was also found that the optimum thickness of inserted GaP to avoid the generation of misfit dislocations is 1 nm.     

CAN总线技术在电控柴油机与ABS/ASR系统匹配中的应用

介绍了采用SAEJ1939汽车通信协议,应用CAN总线技术实现电控柴油机与ABS/ASR系统在整车上匹配的基本原理和方法。通过一个实例,验证了系统的标定、通信测试、模拟测试和车辆测试等匹配过程,并验证方法的正确性和实用性。     

GaAs/Ge solar cell AC parameters at different temperatures

The AC parameters of Gallium Arsenide (GaAs/Ge) solar cell were measured at different cell temperatures (198–348 K) by varying the cell bias voltage (forward and reverse) under dark condition using impedance spectroscopy technique. It was found that the cell capacitance increases with the cell temperature where as the cell resistance decreases, at any bias voltage. The measured cell parameters were used to calculate the intrinsic concentration of electron–hole pair, cell material relative permittivity and its band gap energy. The diode factor and the cell dynamic resistance at the corresponding maximum power point decrease with the cell temperature.     

Optical properties for and intermediate band materials

First-principles calculations of the energy dependent absorption coefficients are presented in this work in order to understand the optical properties of some materials characterized for an intermediate band (IB) with metallic behavior: Ga₃₂P₃₁Cr and Ga₃₁P₃₂Cr. The calculations are based on local spin density approximation and the pseudopotential method using a localized basis set. The resulting optical spectra is analyzed and broken down into the contributions of the different bands and spin components. The results of the electronic properties show that one of the spin components presents an IB, and the absorption coefficients indicate an increase in the absorption sub-gap as a consequence of the optical transitions between the valence and the IB.     

Structural,electronic and optical properties of titania nanotubes

Abstract

This review paper describes primarily recent theoretical calculations with some supporting experimental findings on titania nanotubes. Nanotubes with different types and sizes are discussed in detail in terms of existing theoretical and experimental achievements. Both classical and quantum mechanical simulations are focused on. The properties of these nanotubes have been treated within first principle density functional electronic structure simulation methods. In this paper, we pay particular attention to computational aspects, but when appropriate, relationships with experimental results on titania nanostructures will be mentioned. First, the structural properties of titania nanotubes are reviewed, focusing from experimental growth mechanism to possible theoretical stable structure and orientation. Second, the electronic structure of nanotubes is discussed in terms of band gap modifications of titania and photocatalytic efficiencies in photoelectrochemical devices. Finally, current computational limitations and future directions are described with respect to the performances of nanotube titania based photosensitive devices.