Germanium selective solar absorber surfaces

Thin Ge films, produced by evaporation through 0.3, 1 and 3 torr pressures of argon onto polished aluminum substrates were found to exhibit selective absorption behaviour. Maximum absorptance to emittance ratios of 131 were measured, with values of 81 for films having solar absorptances of 0,9. Film structures were significant in determining collection efficiency. Films deposited at 0.3 torr showed better overall properties due to a larger particle size of about 1 m compared with an approximate 0.1 m size measured with films deposited at 1 and 3 torr.On leave from Australian Atomic Energy Commission, Sydney, Australia.     

AlN/WAlN/W太阳能选择性吸收多层薄膜研究

采用全封闭磁场的非平衡态磁控溅射系统,以纯金属为靶材,制备了AlN/WAlN(多层)/W薄膜。X射线掠射(GID)、扫描电镜(SEM)以及分光光度计等测试手段分析薄膜的相结构、表面形貌以及吸收光谱等特性。结果表明,薄膜沉积设备性能稳定,W、Al靶材溅射率高。获得AlN/WAlN(多层)/W薄膜中各层薄膜表面质地都较均匀,且为多晶态或纳米晶薄膜。该结构膜系对波长在200～2000nm范围内的光波有较高的吸收效果,平均吸收率可达96%以上,吸收性能优异。     

硅表面钝化及对异质结太阳电池特性的影响

研究了不同的晶体硅表面钝化方法,测试分析了硅片的少数载流子寿命以及对晶体硅/非晶硅异质结(HIT)太阳电池性能的影响。发现适当时间的HF溶液处理、氢等离子体处理和表面覆盖约3nm的本征非晶硅层能有效提高硅片的少子寿命,从而提高HIT太阳电池的开路电压。对电池制备工艺综合优化后,得到了基于n型晶体硅的光电转换效率为16.75%(Voc=0.596V,Jsc=41.605mA/cm2,FF=0.676,AM1.5,25℃)的HIT太阳电池。     

Black germanium solar selective absorber surfaces

Semiconductor films with an appropriate bandgap (approximately 0.5-1.25 eV) have a high absorption coefficient in the solar spectral region and high transmission in the IR thermal emission region and thus make nearly ideal selective absorbers when coated on polished metal surfaces with low IR emittance. However, owing to their high refractive index, semiconductor films have high reflectance (approximately 45%) which limits their total solar absorption. We have shown that by controlling the sputtering preparation conditions of non-crystalline germanium films the surface microstructure can be drastically altered by simply etching in 30% H₂O₂. The resulting surface has a total reflectance of less than 3% in the solar spectrum. This flat-back surface appearance is shown to be due to a dense array of aligned needle-like protrusions which have an extremely high aspect ratio and both a cross-sectional area and a separation between needles of the order of the wavelength of solar radiation.     

Evaporated chromium black selective solar absorbers

Chromium blacks made by evaporating chromium metal in low pressures of argon gas, when deposited onto highly reflecting copper substrates, exhibit solar selectivity. The optical and electrical properties and the structure of chromium black films are described, and the absorption mechanism is discussed. The properties of blacks prepared in argon at pressures of $\text{1}\text{2}$ Torr and 3 Torr are compared. This selective surface is easily manufactured and may be suitable for operation at temperatures up to 200 °C in vacuum.     

Characterization of solar selective molybdenum black films

It has been found possible to prepare excellent solar selective molybdenum black films by a modified catholic electrodeposition technique. These films have been characterized using XPS, AES depth profiling, SEM, chemical analysis, X-ray diffraction and VIS-IR reflectance spectroscopy. The study shows that the film is composite of MoO₃ matrix containing fine nickel and copper particles. It is also observed that the copper concentration increases from the surface of the film towards the substrate. Reported solar selectivity can be explained using the Maxwell Gannett theory along with the stacked layer treatment developed by Anderson.     

Limits on the performance of dispersive thin-film stacks

Dispersive thin-film stacks are interesting as compact, cost-effective devices for temporal dispersion compensation and wavelength multiplexing. Their performance depends on the total group delay or spatial shift that can be achieved. For general multilayer stacks, no analytic model exists relating the performance to the stack parameters such as the refractive indices and the number of layers. We develop an empirical model by designing and analyzing 623 thin-film stacks with constant dispersion. From this analysis we conclude that, for given stack parameters, the maximum constant dispersion value is inversely proportional to the wavelength range over which the dispersion is achieved. This is equivalent to saying that, for constant dispersion, there is a maximum possible spatial shift (or group delay) that can be achieved for a given material system and number of layers. This empirical model is useful to judge the feasibility of dispersive photonic nanostructures and photonic crystal superprism devices and serves as a first step in the search for an analytic performance model. We predict that an 8-channel wavelength multiplexer can be realized with a single 21-microm-thick SiO2-Ta2O5 thin-film stack.     

Enhanced performance of SubPC/C60 solar cells by annealing and modifying surface morphology

The performance effect of organic solar cells with subphthalocyanine (SubPC)/fullerene (C60) bilayer was investigated with thermal treatment while changing the vacuum deposition rate of SubPC. The thermal annealing at 100 degrees C increases the optical absorption intensity of SubPC film at the spectral range of 550-630 nm. The X-ray diffraction (XRD) patterns indicates that the thermally annealed film formed the much-ordered morphology, as compared to the non-annealed film. Consequently, thermally treated solar cell exhibited almost 10% higher power conversion efficiency (PCE) compared to the non-annealed device. The fill factor (FF) and PCE of the devices were increased as the deposition rate of SubPC was increased up to 5 A/s and then saturated at higher deposition rates (> 5 A/s). The surface roughness of SubPC films, measured with an atomic force microscope, increased from 1.1 to 5 nm as the deposition rate increased from 1 to 7 A/s. These results imply that rough surface increases the interfacial area between SubPC and C60 and thereby improves the separation of photogenerated electron and hole pairs at the SubPC/C60 interface.     

金属陶瓷太阳能选择吸收性涂层传热研究

在太阳能热利用中,太阳能集热器的传热性能至关重要。本文主要综述了太阳能光谱选择吸收性涂层有效导热系数的理论预测方法、材料制备方法以及实验测量导热系数的方法。文中对多种方法进行了对比,简要分析了各个方法的优缺点。强调了界面接触热阻在复合材料导热中的重要性。最后将理论、制备 、实验三者结合,对未来做出了展望。     

Manganese pigmented anodized copper as solar selective absorber

The study concerns the optical and structural properties of layers obtained by a new efficient surface treatment totally free of chromium species. The process is made up of an anodic oxidation of copper in an alkaline solution followed by an alkaline potassium permanganate dipping post-treatment. Coatings, obtained at the lab and pilot scales, are stable up to 220 °C in air and vacuum, present low emissivity (0.14 at 70 °C) and high solar absorptivity (0.96), i.e. a suitable thermal efficiency (0.84 at 70 °C).     

太阳能光谱选择性吸收涂层研究进展

全面阐述了5种太阳能光谱选择性吸收涂层的作用机理和制备方法,综述了国内外该领域的研究工作和最新研究成果,并对选择性吸收涂层的发展方向进行了探讨。     

Nickel pigmented anodized aluminium as solar selective absorbers

The effect of various impregnation parameters on the structural features and optical properties of solar absorbing nickel pigmented anodic alumina coatings has been studied. The impregnation starts from a threshold voltage. A correlation between microstructural features and the optical properties of these coatings has been established. Stable coating with low emissivity (0.14 at 70°C) and high solar absorptivity (>0.90) have been prepared by anodizing in a phosphoric acid solution.     

Nanocrystalline copper oxide for selective solar energy absorbers

The high-energy edge of the transparency window in nanocrystalline copper monoxide (CuO) can be shifted to 0.6 eV (against 1.45 eV in single crystals). This shift is related to a modification of the shape of the fundamental absorption edge of CuO without any change in the refractive index. The obtained nanocrystalline CuO is recommended for use as a selective solar energy absorber.     

Oxidation of electrodeposited black chrome selective solar absorber films

X-ray photoelectron spectroscopy and Auger electron spectroscopy were used to study the composition and oxidation of electrodeposited black chrome films. The outer layer of the film is Cr₂O₃ and the inner layer is a continuously changing mixture of chromium and Cr₂O₃. Initially, approximately 40 vol.% of the chromium was combined as Cr₂O₃ and the percentage of Cr₂O₃ increased to greater than 60 vol.% after heat treatment for only 136 h at 250°C. After 3600 h at 400°C the percentage of Cr₂O₃ increased to as high as 80 vol.%. The thermal emittance decreased approximately linearly with increasing oxide content whereas the solar absorptance remained constant until the percentage of Cr₂O₃ exceeded approximately 70%. Oxidation was slower when the Cr³⁺ concentration in the plating bath was reduced from 16 to 8 g 1^?1 and when black chrome was deposited on stainless steel rather than on sulfamate nickel.     

远红外频率选择表面的传输特性分析

设计了十字单元的远红外带通型频率选择表面(FSS),并采用模匹配法对其传输特性进行了研究,其中单元中的场分布用有限元法求出。根据此方法研究了不同极化方式的电磁波在斜入射条件下,对不同布阵方式的远红外FSS传输特性的影响。结果发现,无论单元是按正方形布阵还是按正三角形布阵,在电磁波斜入射时中心频率都随入射角的增大而向低频漂移,带宽都相应减小。但无论入射波是什么极化方式,所设计单元按正三角形布阵时的传输特性都比正方形布阵方式稳定。     

Chemically vapor-deposited ZrB2 as a selective solar absorber

Coatings of ZrB₂ and TiB₂ for photothermal solar absorber applications were prepared using chemical vapor deposition (CVD) techniques. Oxidation tests suggest a maximum temperature limit for air exposure of 600 K for TiB₂ and 800 K for ZrB₂. Both materials exhibit innate spectral selectivity with an emittance at 375 K ranging from 0.06 to 0.09, a solar absorptance for ZrB₂ ranging from 0.67 to 0.77 and a solar absorptance for TiB₂ ranging from 0.46 to 0.59 ZrB₂ has better solar selectivity and more desirable oxidation behavior than TiB₂. A 0.071 μm antireflection coating of Si₃N₄ deposited onto the ZrB₂ coating leads to an increase in absorptance from 0.77 to 0.93, while the emittance remains unchanged.     

太阳能选择性吸收薄膜研究进展及展望

太阳能选择性吸收薄膜是太阳能集热器的主要功能组件,是太阳能光热转换中最为关键的部分,也是获得高光热转换效率的重要方式.本文从太阳能选择性吸收薄膜的原理出发,对材料选择、吸收机理以及制备方法等方面进行了介绍,对太阳能选择性吸收薄膜的国内外发展现状进行了论述,同时对限制太阳能选择性吸收薄膜性能的主要因素进行了分析,并对今后的发展进行了展望.