碳化硅零件的激光选区烧结及反应烧结工艺

为了获得高密度、高性能、复杂结构的碳化硅陶瓷件,提出采用机械混合法制备含有黏结剂和乌洛托品固化剂的碳化硅复合粉体,对复合粉体进行激光选区烧结（SLS）形成陶瓷素坯,并对素坯进行气氛烧结和渗硅处理,使其与基体发生反应烧结,最终形成复杂陶瓷异形件。实验证明：若激光功率为8.0 W、扫描速率为2 000 mm/s、扫描间距为0.1 mm、单层厚度为0.15 mm,获得的 SLS 陶瓷样品密度和强度最好。对SLS试样进行合理的中温碳化和高温渗硅,所得碳化硅陶瓷烧结体的抗弯强度最高可达 81 MPa,相对密度大于86%。     

基于TDLAS和ICL的紧凑中红外痕量气体探测系统

为了实现基于可调谐激光吸收光谱技术的高检测灵敏度、低功耗、小型中红外痕量气体传感器设计,结合锑化镓(GaSb)ICL和紧凑型多反射气体吸收气室(MPC)研制了基于不同结构传感光学核的两个小型TDLAS传感系统。两个传感光学核的总功率消耗为3.7 W,并通过探测甲烷(CH4)和甲醛(CH2O)分别验证了双层结构和单层结构系统的性能。实验结果表明:CH4和CH2O系统的检测灵敏度分别为5.0nL/L和3.0nL/L,测量精度分别为1.4nL/L和1.0nL/L。此外,相同配置情况下将两种结构系统应用于甲、乙烷(C2H6)同步检测,通过对校园环境中甲、乙烷进行连续66h的监测试验,验证了设计的紧凑型中红外痕量气体检测系统能够稳定有效地工作,基本满足目前民用气体测量的稳定可靠、精度高、抗干扰能力强等要求。     

Enhanced performance in the deteriorated area of multicrystalline silicon wafers by internal gettering

The deteriorated area of the multicrystalline silicon (mc‐Si) ingots grown by directional solidification, commonly known as the Red Zone, is usually removed before wafering. This area, characterized by poor minority carrier lifetime, is located on the sides, at the top, and the bottom of the mc‐Si ingots. In this study, the effect of internal gettering by oxygen precipitates and structural defects has been investigated on the bottom zone of a mc‐Si ingot. Nucleation and growth of oxygen precipitates as well as low temperature annealing were studied. Photoluminescence imaging, lifetime mapping, and interstitial iron measurements performed by μ‐PCD reveal a considerable reduction of the bottom Red Zone. An improvement of lifetime from below 1 µs to about 20 µs and a reduction of interstitial iron concentration from 1.32 × 10¹³ at/cm³ to 8.4 × 10¹⁰ at/cm³ are demonstrated in this paper. Copyright © 2013 John Wiley & Sons, Ltd.     

Increased conversion efficiency in cadmium telluride photovoltaics by luminescent downshifting with quantum dot/poly(methyl methacrylate) films

Commercially available quantum dots have been encapsulated in a poly(methyl methacrylate) film and used as a luminescent downshifting layer on cadmium sulfide/cadmium telluride photovoltaic devices. Application of these films has resulted in a relative improvement to the short‐circuit current of over 4% by I–V measurement, with a significant increase in the contribution of short‐wavelength light resulting in 25% of the current available in this part of the spectrum being captured. The films have been shown to be highly scattering and the associated difficulties this provides to external quantum efficiency measurements have been discussed. A range of optical characterisation techniques, particularly laser beam induced current, have been used to probe the effect the films have on a cadmium sulfide/cadmium telluride device. An alternate methodology for performing external quantum efficiency measurements with the quantum dot films has been proposed. Copyright © 2013 John Wiley & Sons, Ltd.     

Relation between light trapping and surface topography of plasma textured crystalline silicon wafers

Currently, in the photovoltaic industry, wet chemical etching technologies are used for saw damage removal and surface texturing. Alternative to wet chemical etching is plasma etching. However, as for example, the linear microwave plasma technique, developed by Roth&Rau, has not been implemented in the photovoltaic industry for etching, because of the very low etch rate (<1 µm/min) and the high cost of ownership related to the etching process. In this study, different front surface textured crystalline silicon wafers obtained by means of the linear microwave plasma technique and the expanding thermal plasma technique are investigated in terms of weighted reflection by using reflectometry (250–1200 nm) to study the optical properties of the textures in detail. In addition, atomic force microscopy is used to measure the surface topography to determine statistical roughness parameters, as presented in this paper. Effective light trapping can be obtained by multiple reflections as well as by a graded layer, which leads to a diffuse front surface, or a combination of both. A graded layer can be described as a smooth transition with increasing refractive index from air to silicon with typical thickness of (200 ± 50) nm. We have found that the average plane tilt angle correlates to the measured weighted reflection. Moreover, we can determine from the aspect ratio whether the light trapping is effective by multiple reflections. From the roughness exponent, which is a measure for the micro roughness, we can determine whether the light trapping is effective by a graded layer. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparison of thin epitaxial film silicon photovoltaics fabricated on monocrystalline and polycrystalline seed layers on glass

We fabricate thin epitaxial crystal silicon solar cells on display glass and fused silica substrates overcoated with a silicon seed layer. To confirm the quality of hot‐wire chemical vapor deposition epitaxy, we grow a 2‐µm‐thick absorber on a (100) monocrystalline Si layer transfer seed on display glass and achieve 6.5% efficiency with an open circuit voltage (V_OC) of 586 mV without light‐trapping features. This device enables the evaluation of seed layers on display glass. Using polycrystalline seeds formed from amorphous silicon by laser‐induced mixed phase solidification (MPS) and electron beam crystallization, we demonstrate 2.9%, 476 mV (MPS) and 4.1%, 551 mV (electron beam crystallization) solar cells. Grain boundaries likely limit the solar cell grown on the MPS seed layer, and we establish an upper bound for the grain boundary recombination velocity (S_GB) of 1.6x10⁴ cm/s. Copyright © 2014 John Wiley & Sons, Ltd.     

Silver versus white sheet as a back reflector for microcrystalline silicon solar cells deposited on LPCVD‐ZnO electrodes of various textures

We compare the performance of two back reflector designs on the optoelectrical properties of microcrystalline silicon solar cells. The first one consists of a 5‐µm‐thick low‐pressure chemical vapor deposition (LPCVD)‐ZnO electrode combined with a white sheet; the second one incorporates an Ag reflector deposited on a thin LPCVD‐ZnO layer (with thickness below 200 nm). For this latter design, the optical loss in the nano‐rough Ag reflector can be strongly reduced by smoothing the surface of the thin underlying ZnO layer, by means of an Ar‐plasma treatment. Because of its superior lateral conductivity, the thin‐ZnO/Ag back reflector design provides a higher fill factor than the dielectric back reflector design. When decreasing the roughness of the front electrode with respect to our standard front LPCVD‐ZnO layer, the electrical cell performance is improved; in addition, the implementation of the thin‐ZnO/Ag back reflector leads to a significant relative gain in light trapping. Applying this newly optimized combination of front and back electrodes, the conversion efficiency is improved from 8.9% up to 9.4%, for cells with an active‐layer thickness of only 1.1 µm. We thereby highlight the necessity to optimize simultaneously the front and back electrodes. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization of tandem organic solar cells comprising subcells of identical absorber material

Recently organic tandem solar cells with record efficiency had been shown comprising identical absorber materials in both subcells. Such structures pose new challenges for characterization. The standard test methods for measuring spectral response of tandem solar cells can not be applied. The standard procedures demand for different bias illumination during measuring spectral response allowing to select the subcell being current limiting. With subcells comprising identical absorber materials, thus having identical absorption spectra, such a selection is not trivial. In this paper, we show that with the help of detailed optical simulations of such tandem organic solar cells, their characterization is possible, and we apply the proposed method to a sample structure. Copyright © 2014 John Wiley & Sons, Ltd.     

多层核壳CuInS_2/ZnS量子点的有机相合成的研究

有机相反应体系中合成制备CuInS2量子点核壳结构,并对制备出的核以及核壳结构的材料进行表征。XRD结果显示成功合成纯度高、晶形较好的CIS量子点;通过TEM可以观察到量子点形貌以及尺寸的变化;荧光光谱和吸收光谱则清楚表明在反应过程中红移和蓝移情况以及量子效率的明显增加;最后,由光稳定性实验得出包覆了ZnS的CIS量子点稳定性得到提高。