Growth and properties of SiGe multicrystals with microscopic compositional distribution for high-efficiency solar cells

The growth technique and physical properties of SiGe multicrystals with microscopic compositional distribution are demonstrated for new high-efficiency solar cells in which the wavelength dependence of the absorption coefficient can be freely designed by controlling the compositional distribution in the SiGe multicrystals. This growth technique is suitable for the practical casting method, and it is made up of melt growth of SiGe multicrystals with wide and microscopic distribution of the composition from Si to Ge all over the crystals. It is studied how much widely the microscopic compositional distribution in SiGe multicrystals grown from binary Si–Ge melts can be controlled by the melt composition and the cooling process. The range of the microscopic compositional distribution becomes wider as the starting Si concentration in the growth melt becomes larger. SiGe multicrystals with various microscopic compositional distribution can be freely controlled by optimizing the melt composition and the cooling process. The wavelength dependence of the absorption coefficient of such SiGe multicrystals can also be freely designed. Using the experimentally determined absorption coefficient of a SiGe crystal with microscopic compositional distribution, the short circuit photo-current of solar cells was calculated and it is demonstrated that the short circuit photo-current can be much larger for SiGe with microscopic compositional distribution than for SiGe with uniform composition. Si thin film can be easily grown on such a SiGe multicrystal and the Si/SiGe heterostructure can be obtained. These results show that SiGe multicrystals with microscopic compositional distribution are hopeful for new high-efficiency solar cell applications by using the practical casting method.     

Effect of the compositional distribution on the photovoltaic power conversion of SiGe solar cells

Theoretical investigation on the photovoltaic power conversion of SiGe solar cells was carried out focusing on the impact of the compositional distribution. The absorption coefficient and the intrinsic carrier concentration were assumed to be macroscopically uniform parameters controlled by the compositional distribution. Under an assumption with finite minority carrier diffusion length, solar cell based on SiGe was revealed to have power conversion superior to that based on Si in a limited compositional window on the Si-rich side. In the window, the increase in the photocurrent density overcompensates the decrease in the voltage, and controls the overall conversion efficiency. The width of the window was greatly affected by the compositional distribution in SiGe. A comparison was made with experiments to support the existence of such a compositional window.     

Study of CuInS2/ZnS/ZnO solar cells, with chemically deposited ZnS buffer layers from acidic solutions

Thin film solar cells based on CuInS₂/ZnS/ZnO have been prepared with ZnS buffer film of different thickness. ZnS films are grown by chemical bath deposition (CBD) from acidic solutions of ZnSO₄ and thioacetamide (TA). The change of the growth rate with time is studied by means of the quartz crystal microbalance. Films with different thickness show variable physical, chemical and morphological properties. The structure is studied with X-ray diffraction, showing different crystallinity with deposition time. The absorption coefficient depends also on the CBD deposition time, and shows absorption edges between 2.70 and 3.65 eV. The compositional analysis carried out with XPS (surface) and EDAX (bulk). Bulk composition reflects highly stoichiometric films, with Zn/S ratios close to unit. Preliminary results with CuInS₂-based solar cell show efficiencies around 5%, lower than usually found with standard CdS buffer films (around 9%).     

Characteristics of GaAs solar cells on Ge substrate with a preliminary grown thin layer of AlGaAs

Characteristics of GaAs solar cell on Ge substrate with a new buffer layer structure is reported. The buffer layer structure, which consisted of a preliminarily grown thin layer of A1_xGa_1−xAs and a 1 μm thick GaAs layer, was designed to obtain a high quality GaAs layer on Ge substrate by metalorganic chemical vapor deposition (MOCVD). Performance of a GaAs solar cell fabricated on Ge substrate with the buffer layer structure was compared with that fabricated on Ge substrate with a conventional GaAs buffer layer and also that fabricated on GaAs substrate. A conversion efficiency of 23.18% (AM1.5G) was successfully obtained for the cell fabricated on Ge substrate with the new buffer layer structure, while it was 20.92% for the cell fabricated on Ge substrate with the conventional GaAs buffer layer. Values of V_oc and J_sc, for the cell fabricated on Ge substrate with the new buffer layer structure were approximately comparable to those of a 25.39% efficiency GaAs solar cell fabricated on GaAs substrate.     

一种高精度的太阳跟踪方法

为提高太阳能利用率,提出了同时使用视日跟踪和光电跟踪的太阳跟踪新方法。为提高视日跟踪精度,对常见的太阳位置算法仿真比较,得到实用的太阳位置高精度混合算法;同时,设计了特制的四象限硅光电池,对视日跟踪进行误差修正,从而实现了太阳精确跟踪。理论分析和设计表明,该方法能够实现高精度、全天候地自动跟踪太阳,易于推广应用。     

离心铸造太阳电池硅片液态成形机制的研究

为了将离心铸造技术成功地移植到低成本超薄多晶太阳电池硅片的成形工艺上，提出了ＥＬＣＣ技术的硅片液态成形方法，即将铸模型腔预热至硅熔点以上温度，过热的硅液被浇注到型腔后，在离心力的作用下始终保持液态充型。这种成形机制易于实现厚度小于１ｍｍ的硅片的完整成形，而且对模具转速、硅液过热度等要求较低。采用该方法，硅片的成形与结晶不会同时发生，可以在硅片液态成形后，采用定向凝固的方法获得粗大的定向柱晶组织，提高硅片的光伏性能。采用理论分析、计算机模拟与工艺实验相结合的方法，对ＥＬＣＣ技术硅片液态成形机制进行了研究，为进一步对硅片凝固过程组织控制的研究奠定基础。     

The Calculation of Cumulative Distribution Function of Water Vapor Using Modified Bandwidth

1ntroductionIn many high temPerature processes radiation is thedondnant mode of heat transfer, and much effort hasbeen aPplied to develop methods of Predction forradiative heat exchange. Because of the non-graybehavior of typical combustion products such as watervapor and carbon dioxide, the complicated spectrabehavior must be presented if accurate radiative heattransfer calculations have to be cAned out.The complex spectral dependence of the absorptioncoefficient makes the detednation of spe…     

Optical efficiency analysis of cylindrical cavity receiver with bottom surface convex

The bottom surface of conventional cavity receiver cannot be fully covered by coiled metal tube during fabrication, which would induce a dead space of solar energy absorption. The dead space of solar energy absorption can severely decrease the optical efficiency of cavity receiver. Two new types of cavity receiver with bottom surface convex are put forward with the objective to solve the problem of dead space of solar energy absorption and improve the optical efficiency of cavity receiver. The optical efficiency and heat flux distribution of the two new types of cavity receiver are analyzed by Monte Carlo ray tracing method. Besides, the optical efficiency comparisons between conventional cavity receiver and the two new types of cavity receiver are conducted at different characteristic parameter conditions.     

Spectral transmittance of water and sodium chloride water solution as working substance for a solar pond

The transmission properties of water and sodium chloride water solutions with various salt concentrations were investigated. This paper concerns the measurement of the spectral transmittance and the calculation of the total transmittance for water and NaCl water solutions. The spectral transmittance of the NaCl water solutions over the infrared and nearby regions increased with increasing salt concentration for constant specimen thickness and air mass. The spectral transmittance was found to be useful for precisely calculating the thermal performance of a solar pond, and by using an effective absorption coefficient, a five-partition method dividing the wavelengths into five bands by which the total transmittance up to a water depth of 3 m could be calculated, was found to be important as a practical method of solar pond technology. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 26(1): 1–15, 1997     

Enhancement of solar radiation absorption using nanoparticle suspension

The radiation absorption characteristics of a Ni nanoparticle suspension were investigated by spectroscopic transmission measurement. It was demonstrated that the absorption coefficient of the nanoparticle suspension is much higher than that of the base liquid for visible to near-infrared wavelengths. Radiation characteristics predicted by the Mie theory showed good agreement with the increase of absorption coefficient in wavelengths where the base liquid is transparent. It was also confirmed that a new transmittance measurement technique for a liquid sample using a liquid cell with no spacer was quite useful for evaluating a material possessing an extremely strong absorption band. The proposed measurement method and successive Kramers-Kronig analysis were validated by measuring the optical properties of water. The measurement and prediction process of the thermal radiation properties of nanoparticle suspensions developed here could be used in developing direct absorption solar collectors.     

电磁悬浮熔炼离心铸造设备的研制

电磁悬浮熔炼离心铸造（ＥＬＣＣ）技术是大幅度降低太阳电池硅片成本的一条新途径。报道了该设备的研制及总体设计方案，介绍了炉体、电源系统、机械系统、辅助系统及其相互配合。该设备已应用于ＥＬＣＣ技术及其相关工艺的研究。     

Titania–germanium nanocomposite as a photovoltaic material

Titania–germanium (TiO₂–Ge) nanocomposite, which comprises Ge nanodots in the TiO₂ matrix, is an interesting optoelectronic material. We can easily tailor the structural, optical and electronic properties of the nanocomposite thin films in a wide range by customizing the density and size of Ge dots. The promising properties encouraged us to fabricate solar cells with TiO₂–Ge nanocomposites. We fabricated p-Si/TiO₂–Ge heterojunction solar cells. The preliminary characterizations of these devices show us the promise of TiO₂–Ge nanocomposites for the photovoltaic application.     

Germanium-doped Czochralski silicon for photovoltaic applications

Germanium (Ge)-doped Czochralski (GCZ) silicon has been grown for photovoltaic (PV) applications. It is found that Ge doping improves the mechanical strength of CZ silicon, resulting in the reduction of breakage during wafer cutting, cell fabrication and module assembly. Boron-oxygen (B-O) defects that lead to the light-induced degradation (LID) of carrier lifetime are effectively suppressed by Ge doping. The decrease in the maximum concentration of B-O defects increases with an increase of Ge concentration. The efficiency of GCZ silicon solar cells and the power output of corresponding PV modules both exhibit smaller loss under sunlight illumination. The current work suggests that GCZ silicon should be potentially a novel substrate for thin solar cells with low LID effect.     

Single crystal growth and properties of γ-phase in the CuInSe2+2CdS⇔CuInS2+2CdSe reciprocal system

The intermediate solid solution, γ-phase, exists in the CuInSe₂+2CdS⇔CuInS₂+2CdSe reciprocal system. It crystallizes in the cubic structure and has a wide homogeneity range. Single crystals of the γ-phase are grown by a modified Bridgman method and their composition, crystal structure, optical and electrical properties are studied. The band gap varies from 1.43 to 1.05 eV along the ‘Cu₃Cd₂In₃S₈’-‘CuCd₂InSe₄’ compositional section. The crystals are photosensitive, mostly p-type, with hole concentrations in the 10¹⁵-10¹⁶ cm⁻³ range and mobilities up to 18 cm²/V s. The results indicate that the γ-phase can be considered as a new absorbing material for thin-film solar cells.     

Experimental characterization of the heat transfer in a free-falling-particle receiver

This paper describes the measurements performed on a Free Falling curtain of spherical beads being irradiated in a high-flux solar furnace. The curtain of spherical beads is part of a direct absorption solar receiver concept, which replaces the conventional water and steam receiver (DAR) and is potentially more efficient and less expensive than a conventional receiver. To adequately describe a DAR a series of experiments have been designed and implemented to measure radiative heat flux and particle temperatures. The extinction coefficient for the DAR bead curtain has also been measured. These data and results along with a new method for measuring bulk bead temperature will be discussed. A method is also described which uses the angular distribution of incoming radiative heat flux to estimate the incoming intensity field.     

Effect of light scattering on the performance of a direct absorption solar collector

Recently, a solar thermal collector often employs nanoparticle suspension to absorb the solar radiation directly by a working fluid as well as to enhance its thermal performance. The collector efficiency of a direct absorption solar collector (DASC) is very sensitive to optical properties of the working fluid, such as absorption and scattering coefficients. Most of the existing studies have neglected particle scattering by assuming that the size of nanoparticle suspension is much smaller than the wavelength of solar radiation (i.e., Rayleigh scattering is applicable). If the nanoparticle suspension is made of metal, however, the scattering cross-section of metallic nanoparticles could be comparable to their absorption cross-section depending on the particle size, especially when the localized surface plasmon (LSP) is excited. Therefore, for the DASC utilizing a plasmonic nanofluid supporting the LSP, light scattering from metallic particle suspension must be taken into account in the thermal analysis. The present study investigates the scattering effect on the thermal performance of the DASC employing plasmonic nanofluid as a working fluid. In the analysis, the Monte Carlo method is employed to numerically solve the radiative transfer equation considering the volume scattering inside the nanofluid. It is found that the light scattering can improve the collector performance if the scattering coefficient of nanofluid is carefully engineered depending on its value of the absorption coefficient.     

Electronic and optical analysis of high-efficiency photovoltaic materials based on a GaN semiconductor

An ab initio study using the local spin density approximation of the electronic and optical properties of materials where Cr transition metal substitutes for N in the GaN host semiconductor with an atomic concentration of 1.56% is presented. This material, characterized by an isolated and partially filled intermediate band, is a candidate for high-efficiency solar cells. The atomic and orbital composition of this band has been analyzed showing that is mainly made up of a t-group orbital of the transition metal. The absorption coefficient theoretical results show a sub-gap absorption with respect to the host semiconductor which could lead to an increase in solar conversion efficiency.     

新型平板式太阳能冷热联供装置

在积累了太阳固体吸附式制冷循环研究的基础上，与现有的平板式太阳热水器制造技术紧密结合，提出了平板式太阳冷热联供循环方式，并在实验室内成功地制作了实物样机。该装置能有效地回收太阳固体吸附式制冷不中吸附床的显热及吸附热，且操作简便。实验结果有效地支持了所提出的设想，为太阳固体吸附式制冷的实用化应用打下了良好基础。     

三结太阳电池低频噪声特性与可靠性表征研究

以GaInP/InGaAs/Ge三结太阳电池为研究对象,通过宽范围电流偏置条件下的低频噪声测试和高温应力试验,对三结太阳电池的低频噪声特性和可靠性表征进行研究分析.结果表明,三结太阳电池的低频噪声包括1/f噪声和G-R噪声.在宽范围电流偏置条件下,低频噪声随偏置电流呈先增大后减小的规律,并在频率为500 Hz时出现G-...     

太阳能溴化锂吸收式制冷技术的研究进展

介绍了太阳能澳化锂吸收式制冷循环的工作原理和系统构成,具体阐述了该制冷循环的几种典型结构,包括单效、双效、两级以及三效涣化锂吸收式制冷循环,分析了各种制冷循环的优缺点以及目前研究进展;进一步讨论了太阳能澳化锂吸收式制冷机组的性能特点受冷媒水出口温度、冷却水进口温度、加热蒸汽温度、污垢系数及不凝性气体等诸多因素的影响;提出了太阳能溴化锂吸收式制冷技术现存问题,最后指出,随着科学技术的发展和绿色建筑的兴起,太阳能溴化锂吸收式制冷将会有非常大的发展前景。