A Novel Comparative Photothermal Method for Measuring Thermal Diffusivity

A novel comparative method has been developed at the National Physical Laboratory (NPL) to measure the thermal diffusivity of semi-infinite samples without a priori knowledge of the boundary conditions. It is based on photothermal radiometry, and involves the detection of modulated thermal radiance from a target irradiated by a modulated, focused diode laser beam with a power of 1W. The technique exploits the fact that the frequency response of the surface temperature modulation scales with thermal diffusivity for a given target geometry (this is a fundamental property of the heat diffusion equation). In the process two samples are measured, one of which is known, and the diffusivity of the second material is derived from scaling the results over frequency. Measurements on samples of platinum and Inconel have shown the validity of the methodology but also raised issues concerning the difficulty of accurate measurements due to surface coatings or roughness.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22--27, 2003, Boulder, Colorado, U.S.A.     

塔式太阳能热发电吸热器模拟计算

本文建立了塔式太阳能热发电高温吸热器传热性能数值计算模型,采用有限元分析方法进行模拟计算,编制了预测塔式太阳能热发电吸热器热工模拟程序。本文在综合考虑多场耦合特性的情况下,研究了吸热器单模块周向非均匀热流边界条件下吸热介质对流换热系数、吸热管外壁温度、光热转化效率的数值及分布。数值模拟为工程设计提供可靠的科学依据,为塔式太阳能热发电整体控制策略的制定提供参考。     

柔性聚酰亚胺衬底非晶硅薄膜太阳电池空间可靠性研究

重点分析了柔性聚酰亚胺衬底非晶硅太阳电池的结构、材料和工艺特点,认为非晶硅薄膜制备工艺和材料本身、聚酰亚胺以及其他封装材料是影响柔性聚酰亚胺衬底非晶硅太阳电池可靠性的关键因素。研究了这些关键材料的典型失效模式及其对柔性聚酰亚胺衬底非晶硅太阳电池可靠性的影响。初步探讨了提高电池空间可靠性的新工艺和新材料。     

太阳电池用非晶碳薄膜在黑硅衬底上的生长

利用微波等离子体化学气相沉积(MPCVD)法在黑硅和抛光单晶硅片衬底上生长非晶碳薄膜,其中变量为CH4流量,分别为10sccm、14sccm、18sccm、22sccm、26sccm.通过扫描电子显微镜(SEM)、X射线衍射分析(XRD)、原子力显微镜(AFM)、拉曼光谱表征了非晶碳薄膜的结构和形貌特征.结果表明,在650℃时随着CH4流量的逐渐增加,在平整的非晶碳薄膜上C-C的sp2相团簇颗粒的直径逐渐变大.AFM测试结果显示,非晶碳薄膜表面的平均粗糙度(Ra)为0.494nm.     

Charge Transfer from Carbon Nanotubes to Silicon in Flexible Carbon Nanotube/Silicon Solar Cells

Mechanical fragility and insufficient light absorption are two major challenges for thin flexible crystalline Si‐based solar cells. Flexible hybrid single‐walled carbon nanotube (SWNT)/Si solar cells are demonstrated by applying scalable room‐temperature processes for the fabrication of solar‐cell components (e.g., preparation of SWNT thin films and SWNT/Si p–n junctions). The flexible SWNT/Si solar cells present an intrinsic efficiency ≈7.5% without any additional light‐trapping structures. By using these solar cells as model systems, the charge transport mechanisms at the SWNT/Si interface are investigated using femtosecond transient absorption. Although primary photon absorption occurs in Si, transient absorption measurements show that SWNTs also generate and inject excited charge carriers to Si. Such effects can be tuned by controlling the thickness of the SWNTs. Findings from this study could open a new pathway for designing and improving the efficiency of photocarrier generation and absorption for high‐performance ultrathin hybrid SWNT/Si solar cells.     

A Novel Ultra-Low Work Function TbFx for High Efficiency Dopant-Free Silicon Solar Cells

The ability of carrier selective contact is mainly determined by the surface passivation and work function for dopant-free materials applied in crystalline silicon (c-Si) solar cells, which have received considerable attention in recent years. In this contribution, a novel electron-selective material, lanthanide terbium trifluoride (TbF_x), with an ultra-low work function of 2.4 eV characteristic, is presented, allowing a low contact resistivity (ρ_c) of ≈3 mΩ cm². Additionally, the insertion of ultrathin passivated SiO_x layer deposited by PECVD between TbF_x and n-Si resulted in ρ_c only increase slightly. SiO_x/TbF_x stack eliminated fermi pinning between aluminum and n-type c-Si (n-Si), which further enhanced the electron selectivity of TbF_x on full-area contacts to n-Si. Last, SiO_x/TbF_x/Al electron-selective contacts significantly improves the open circuit voltage (V_oc) for silicon solar cells, but rarely impacts the short circuit current (J_sc) and fill factor (FF), thus champion efficiency cell achieved approaching 22% power conversion efficiency (PCE). This study indicates a great potential for using lanthanide fluorides as electron-selective material in photovoltaic devices.     

Multi-Carrier Generation in Organic-Passivated Black Silicon Solar Cells with Industrially Feasible Processes

The innate inverse Auger effect within bulk silicon can result in multiple carrier generation. Observation of this effect is reliant upon low high-energy photon reflectance and high-quality surface passivation. In the photovoltaics industry, metal-assisted chemical etching (MACE) to afford black silicon (b-Si) can provide a low high-energy photon reflectance. However, an industrially feasible and cheaper technology to conformally passivate the outer-shell defects of these nanowires is currently lacking. Here, a technology is introduced to infiltrate black silicon nanopores with a simple and vacuum-free organic passivation layer that affords millisecond-level minority carrier lifetimes and matches perfectly with existing solution-based processing of the MACE black silicon. Advancements such as the demonstration of an excellent passivation effect whilst also being low reflectance provide a new technological route for inverse Auger multiple carrier generation and an industrially feasible technical scheme for the development of the MACE b-Si solar cells.     

Photothermal Techniques for Thermal Characterization of Linear Alcohols

Photothermal techniques were used for the thermal characterization of linear alcohols. This was carried out by measuring the thermal diffusivity (by means of a photopyroelectric technique) and thermal effusivity (by means of a photoacoustic technique) of ten linear alcohols, from methanol to 1-decanol. The thermal conductivity and specific heat for these substances were obtained by means of their relations with the two previous thermal properties, by using the values reported for the densities of the alcohols. The values of thermal effusivity showed a decreasing behavior with the increase in length of the linear molecule, and the values of thermal diffusivity, on the other hand, showed a similar behavior but only up to 1-pentanol, from which these values began to increase; this latter behavior was also observed, although to a lesser extent, for thermal conductivities. This peculiar behavior for thermal diffusivity and thermal conductivities is attributed to the influence of the hydroxyl group, which is strong for low molecular weight alcohols, but it diminishes as the size of alcohol’s molecule increases.     

非晶硅太阳电池伏-安特性曲线的测定

本工作建立了 AM1光谱条件下可调光照强度,采用补偿线路,自动测绘电池在亮场和暗场时连续的三象限伏—安特性曲线的设备。并在该设备上测量了单晶硅和 p~+-i-n~+非晶硅太阳电池的各项特性参数。     

n型层对柔性衬底微晶硅太阳电池特性的影响

在不锈钢柔性衬底上采用等离子体化学气相沉积(PECVD)方法制备了不同结构的n型硅薄膜,测试了在其上生长的微晶硅太阳电池的电学输出特性.发现太阳电池的开路电压随n型层的硅烷浓度线形变化,短路电流密度则存在一个最优值,这与n型层引起的本征层中的孵化层和结构演变有关.将优化后的n型层应用于不锈钢柔性衬底的非晶硅/微晶硅叠层...     

Temperature Dependence of Photothermal Displacement Signal in Silicon

Abstract

This letter presents the preliminary results of a study on the dependence of photothermal displacement signal on temperature in crystalline silicon wafers and coated silicon samples. The temperature enters indirectly into the signal as thermal conductivity, specific heat and thermal expansion coefficient of the material vary with temperature. The experimental results are consistent with that theoretically expected by taking into account the dependence of thermal conductivity from dopant concentration at low temperatures.     

Preparation of High-Purity Silicon for Solar Cells

This article addresses the problems in the preparation of high-purity silicon for solar cells. The growing application field of silicon solar cells requires a substantial reduction in the cost of semiconductor-grade silicon, which is currently produced by the classical trichlorosilane process. Here, we analyze alternative processes for the preparation of solar-grade silicon: the reduction of volatile silicon compounds, refining of metallurgical-grade silicon, reduction of silicon fluorides, and reduction of silicon dioxide. We believe that carbothermal reduction followed by the refining of melted silicon is the most attractive process from the viewpoint of manufacturing cost.     

Black Nickel Coatings for Solar Collectors

Black nickel alloy coatings suitable for solar collectors were produced by electrodeposition from baths containing Ni and Zn sulfates and thiocynate. Variables having the greatest influence on optical properties of the black deposits are: pH-value, temperature, zinc and thiocyanate concentration. Of particular importance is the plating current which is related to the cathode potential that controls the composition, and alternatively, the optical properties of the deposited coatings.

The mechanism of blackening of the Ni coatings was attributed to the deposition of sulfide particles with Ni-Zn alloy. It was shown that, in absence of thiocyanate, co-deposited Zn causes a degree of blackening to Ni coatings due to the deposition of Ni₃Zn₂₂ as identified by x-ray phase analysis. Considerable blackening can be achieved by sulfur, which is deposited as Ni₃S₂. In a modified composition it was possible to replace sulfur by phosphorous supplied to the coating by the addition of sodium hypophosphite to the plating solution.

The coatings were of optimum optical properties as far as maximum absorptance and minimum emittance. Absorptance values as high as 0.93 could be obtained for selective coatings (2-3 microns thick) deposited under optimized conditions. Performance tests for coated solar water heater panels showed that the coatings are well qualified. The endurance of the coatings was evaluated in actual service conditions with regard to thermal degradation and corrosion resistance.     

双纳米硅p层优化非晶硅太阳能电池

采用等离子体增强化学气相沉积(Plasma Enhanced Chemical Vapor Deposition,PECVD)技术在高功率密度、高反应气压和低衬底温度下制备出不同氢稀释比RH的硅薄膜.高分辨透射电镜(High-Resolution Transmission Electron Microscopy,HRT...     

A Novel Procedure for Receiver Noise Characterization

The noise figure at one value of source admittance, plus the variation of output noise power with source admittance, are sufficient for the complete noise characterization of a linear receiver. A standard noise generator of variable admittance is not required. A wide range of source admittances can be used.     

硅半导体太阳能电池进展

太阳能电池是将太阳能直接转化为电能的装置,也是有效利用太阳能最佳途径之一。作为一种绿色能源,尤其是在核电安全问题面临挑战的今天,太阳能电池被认为是解决能源衰竭和环境污染等一系列重大问题的最佳选择。目前,许多国家正在制订中长期太阳能开发计划,准备在21世纪大规模开发太阳能。当前研究最多同时在生产应用的最广泛的当数硅太阳能电池(如单晶硅、多晶硅、非晶硅等)。通过对各类硅太阳能电池的性能、工艺、转化效率以及制备方法等方面作比较并讨论了它们各自性能的优劣,最后结合当前国内外工业化生产状况,对硅太阳能电池研究现状和各自的最新进展作了比较详细的综述,并简要讨论了硅太阳能电池研究和生产上的前景及趋势。