太阳电池中CdTe多晶薄膜沉积制备及其性能

在氩氧混合气氛下近空间升华技术(CSS)制备CdTe多晶薄膜中，薄膜的结构、性质决定于整个沉积过程深入研究沉积过程中的热交换、物质输运，有助于制备薄而致密的具有进行良好光电性质CdTe薄膜．通过分析近空间沉积的物理机制，测量近空间沉积装置内温度分布，对升温过程、气压与薄膜初期成核的关系进行讨论。研究结果表明，不同气压下制备的样品，均有立方相CdTe，此外，还有CdS和SnO2：F衍射峰，CdTe晶粒随气压增加有减小趋势；随气压的增加．透过率呈下降趋势，相应的CdTe吸收边向短波方向移动。在此基础上制备出转换效率优良的结构为SnO2：F／CdS／CdTe／Au的串联集成电池。     

Manufacturing of CdTe thin film photovoltaic modules

The technology to fabricate CdTe/CdS thin film solar cells can be considered mature for a large-scale production of CdTe-based modules. Several reasons contribute to demonstrate this assertion: a stable efficiency of 16.5% has been demonstrated for 1 cm² laboratory cell and it is expected that an efficiency of 12% can be obtained for 0.6 × 1.2 m² modules; low cost soda lime float glass can be used as a substrate; the amount of source material is at least 100 times less than that used for single crystal modules and is a negligible part of the overall cost. The fabrication process can be completely automated and a production yield of one module every 2 min can be obtained, which implies a production cost substantially less than 1€/W_P. A further cost reduction will render this kind of energy production competitive with the energy obtained from fossil fuels by approaching the so-called grid-parity. Some new companies have recently announced the start of production or plan to do so in the near future. Many of these plants are located in Germany, some in the USA. In Italy, a new company has been constituted in 2008, with the aim of building a factory with a capacity of 18 MW/year. In this article, we will describe and compare the basic principles of CdTe solar cells and modules. We will include an overview of the potentials of these technologies and of the R&D issues under investigation. This paper describes how the large-area mass production of CdTe solar modules is realized in the Italian factory and presents a worldwide overview of the current production activities.     

影响硫化镉/碲化镉性能的关键制备技术探讨

CdTe多晶薄膜具有接近理想光谱响应状态的禁带宽度(1.45eV)和高达10-5cm-1的光吸收系数,是较具前途的光伏材料,而CdTe薄膜太阳能电池由于具有低的制造成本和高的转换效率,使其成为最具发展前途的薄膜太阳能电池。CdS和CdTe膜层的质量对CdTe薄膜太阳能电池的性能有很大影响,如何完善CdS和CdTe的制备技术,获得高质量的膜层,引起了广泛关注。笔者综述了影响CdS和CdTe质量的关键制备因素,提出了一些新的制备方法。     

Development of an energy-binned photon-counting detector for X-ray and gamma-ray imaging

The aim of this study is to develop an energy-binned photon-counting (EBPC) detector that enables us to provide energy information of x-rays with a reasonable count statistics. We used Al-pixel/CdTe/Pt semiconductor detectors, which had an active area of 8 mm×144 mm and consisted of 18 modules aligned linearly. The size of a CdTe detector module was 8 mm×8 mm and the thickness of the CdTe crystal was 1 mm. Each module consisted of 40×40 pixels and the pixel size was 200 μm×200 μm. We applied the bias voltage of −500 V to the Pt common electrode. The detector counted the number of x-ray photons with four different energy windows, and output four energy-binned images with pixel depths of 12, 12, 11 and 10 bits at a frame rate of 1200 Hz (300 Hz×4 energy bins). The basic performance of the detector was evaluated in several experiments. The results showed that the detector realized the photon counting rate of 0.4×10⁶ counts/sec/pixel (10⁷ counts/sec/mm²), energy resolution 4.4% FWHM at 122 keV. The integral uniformity of the detector was about 1% and the differential uniformity was about 1%. In addition, the image quality was examined with a resolution chart and step-wedge phantoms made of aluminum and polymethyl methacrylate. And we compared the quality of an acquired image with that acquired with an energy integration detector. The results of these experiments showed that the developed detector had desirable intrinsic characteristics for x-ray photon counting imaging.     

Facile synthesis and characterization of CdTe quantum dots–polystyrene fluorescent composite nanospheres

A novel method for the synthesis of CdTe quantum dots–polystyrene (CdTe/PS) composite nanospheres was developed by a two-step route. The as-prepared composite nanospheres were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), fluorescent microscope imaging and fluorescence spectrometer. The results showed that the composite nanospheres were spherical and relatively uniform with a diameter of 120 nm. Compared with previous methods, the proposed method was simple, efficient and inexpensive, moreover the composite nanospheres exhibited favorable water-dispersible, stable, size-tunable and fluorescent properties.     

Deposition of tellurium films by decomposition of electrochemically-generated H2Te: application to radiative cooling devices

The preparation of homogenous, large area thin layers of tellurium on thin polyethylene foils is described. The tellurium was formed by room temperature decomposition of electrochemically generated H₂Te. Pre-treatment of the polyethylene substrates with KMnO₄ to give a Mn-oxide layer was found to improve the Te adhesion and homogeneity. Optical characterization of the layers was performed using UV/VIS/NIR spectroscopy. Such coatings have favorable characteristics for use as solar radiation shields in radiative cooling devices. The simplicity of generation of the very unstable H₂Te was also exploited to demonstrate formation of size-quantized CdTe nanocrystals.     

Hybrid photovoltaic cells with II–VI quantum dot sensitizers fabricated by layer-by-layer deposition of water-soluble components

We present the fabrication of all solid state heterojunction photovoltaic devices consisting of TiO₂ films sensitized by colloidal CdSe and CdTe quantum dots (QDs) and a hole transport layer of the conjugated polymer poly(9,9-dioctyl-fluorene-co-N-(4-butylenphenyl)diphenylamine). The sensitized films were prepared by alternating the layer-by-layer deposition of TiO₂ nanoparticles, water-soluble semiconductor QDs and polycations. Photovoltaic devices sandwiched between fluorinated tin oxide and gold electrodes showed a high rectification ratio and photovoltages of up to 1.15 V. Effective sensitization was observed for CdSe QDs, while incorporated CdTe QDs apparently had no such effect. These findings are explained by confinement effects in QDs.     

Magneto-Optical Study of Diluted Magnetic Semiconductor Nanostructures Prepared by Pulsed Laser Deposition

The CdTe/Cd_1–x Mn _x Te quantum well structures have been grown by pulsed laser deposition. X-ray diffraction analysis demonstrates high structural quality of the deposited layers and nanostructures. In the magnetoabsorption spectra the large Zeeman splitting of exciton peak which is corresponded to the heavy-hole exciton transition in the CdTe quantum well layers is revealed. The Faraday rotation spectra of the superlattices is interpreted in framework of the exciton transition for the Cd_1–x Mn _x Te layers at a higher photon energy. Influence of different factors on behavior of the Zeeman splitting and the Faraday rotation in the studied nanostructures is discussed.     

Thickness-dependence of stoichiometry and microstructure characteristics in correlation with conductivity type of CdTe films

CdTe films were prepared by physical vapour deposition on a substrate at room temperature (RT) as well as on a cold (LT) one using low deposition rate. The thickness-dependence of stoichiometry revealed an abrupt decrease in the Cd/Te ratio as the thickness increases. Change of thickness did not affect the type of observed (111) crystallographic texture, only the degree of preferred orientation is enhanced as the film grows. The internal strain was negligible while the crystallite size increased rapidly at small thickness (up to 400 nm), and less thickness dependence was observed with further film growth. However, thickness dependence of lattice parameters showed a minimum and a maximum at approximately 300 nm in the case of RT and LT, respectively. The observed change in conductivity from n- to p-type and its vital correlation with the stoichiometry and structural characteristics were presented. Based on thickness dependence of stoichiometry and lattice parameters as well as the conductivity type, formation and annihilation of lattice defects were considered.     

The use of aluminium doped ZnO as transparent conductive oxide for CdS/CdTe solar cells

CdTe/CdS and CdTe/ZnO thin film solar cells were grown with a high vacuum evaporation based low temperature process (≤ 420 °C). Aluminium doped zinc oxide (AZO) was used as transparent conducting oxide (TCO) material. AZO exhibited excellent stability during the solar cell processing, and no significant change in electrical conductivity or transparency was observed. The current density loss due to absorption in the 1 μm thick AZO layer with 5 Ω per square sheet resistance was found to be 1.2 mA/cm². We investigated the influence of an intrinsic ZnO layer (i:ZnO) in combination with various CdS thicknesses. The i:ZnO layer was found to significantly increase the open circuit voltage of the solar cells with very thin CdS layer. Increasing thickness of the i:ZnO layer leads to UV absorption losses, narrowing of the depletion layer width and hence reduced collection efficiency in the long wavelength (685-830 nm) part. With AZO/i:ZnO bi-layer TCO we could achieve cell efficiencies of 15.6% on glass and 12.4% on the flexible polyimide film.