利用高度稳定的发光薄膜提高多晶硅太阳能电池的光伏效率（英文）

硅基太阳能电池已经主导了整个光伏市场,但是仍然面临着光电转化效率低的问题,其中部分原因是其对紫外线的利用率较低.稀土铕配合物能够将紫外光转化为可见光,有望提高硅基太阳能电池的光电转化效率.然而,这类配合物较低的稳定性限制了它们的实际应用.本文中,我们制备了一种高度稳定的EVA/Eu(ND)4-CTAC发光薄膜,将其覆盖在大尺寸的多晶硅太阳能电池表面(110 cm^2)可以使得光电转化效率从15.06%提高到15.57%.在500 h的加速老化实验中荧光性能几乎没有下降,证明了发光薄膜的超强稳定性.在如此大的有效面积上,发光薄膜使硅基太阳能电池的转换效率提高0.51%的绝对值,同时实现超高的稳定性,说明该发光膜在光伏工业上具有广阔的应用前景.     

Metamaterial-plasmonic absorber structure for high efficiency amorphous silicon solar cells

We show that a planar structure, consisting of an ultrathin semiconducting layer topped with a solid nanoscopically perforated metallic film and then a dielectric interference film, can highly absorb (superabsorb) electromagnetic radiation in the entire visible range, and thus can become a platform for high-efficiency solar cells. The perforated metallic film and the ultrathin absorber in this broadband superabsorber form a metamaterial effective film, which negatively refracts light in this broad frequency range. Our quantitative simulations confirm that the superabsorption bandwidth is maximized at the checkerboard pattern of the perforations. These simulations show also that the energy conversion efficiency of a single-junction amorphous silicon solar cell based on our optimized structure can exceed 12%.     

Vacuum-deposited polycrystalline silicon solar cells on foreign substrates

The problem of fabricating low cost solar cells on foreign substrates has been addressed through the use of vacuum-deposited polycrystalline silicon films. The experimental cells consisted of the following layers on an Al₂O₃ substrate: TiB₂ bottom electrode/p-type polycrystalline silicon film/n-type silicon region/Ti---Ag electrode. The formation and properties of each layer are described. Interfacial reactions and purity were examined by secondary ion mass spectrometry, X-ray diffraction and scanning electron microscopy. A reactionbettween silicon and TiB₂ resulting in large silicon crystallite growth has been identified. The n-type region was formed by standard phosphorus diffusion techniques. Typical photovoltaic responses without an antireflection coating were V_oc = 0.28 V, J_sc = 18 mA cm^-2, an efficiency of 2.7% and a fill factor of 0.55. The factors limiting the cell efficiency were primarily the grain size and the purity of the p-type silicon layer.     

High efficiency amorphous silicon solar cells with high absorption coefficient intrinsic amorphous silicon layers

This paper considers the intrinsic layer of hydrogenated amorphous silicon (a-Si:H) solar cells. The deposition temperatures (T_d) and electrode distances (between cathode and anode, E/S) are important factors for a-Si:H solar cells. Thus, this study examines the effects of deposition temperatures and electrode distances in the intrinsic layer of a-Si:H solar cells with regard to enhanced the short-circuit current density (J_sc) and thereby conversion efficiency. It is shown that the J_sc of a-Si:H solar cells can be increased by proper choice of T_d and E/S of the i-a-Si:H layers. The J_sc of the a-Si:H solar cells is largely dependent on light absorption of the i-a-Si:H layer. It is demonstrated that the absorption coefficient in an i-a-Si:H layer can be increased to provide higher J_sc under fixed thickness. Results show that the optimized parameters improve the J_sc of a-Si:H solar cells to 16.52 mA/cm², yielding an initial conversion efficiency of 10.86%.     

Effect of porous silicon stain etched on large area alkaline textured crystalline silicon solar cells

This work shows the effects of porous silicon stain etched on alkaline textured antireflection coatings of large area monocrystalline silicon solar cells. The texturization process has been produced by immersion of the silicon wafers in different carbonate-based solutions. The porous silicon layers were formed by stain etching in a HNO₃/HF aqueous solution before or after the texturization process. We study the effects of different alkaline and acidic solutions and the etching times on the solar cell parameters and the surface reflectance of the device. We have found that the average reflectance of the surface is lowered when the porous etching is combined with the texturization in the alkaline solution. However, the solar cell characteristics are not improved.     

低压压印制备硅点阵结构的工艺研究

高密度、图形规则的硅点阵结构由于其独特的光电性能具有广泛的应用前景.本文介绍了一种以低压压印结合反应离子刻蚀制备硅点阵的方法,即利用PDMS模板通过压印复制获得PMMA掩模结构,用反应离子刻蚀在硅片表面制得高度有序的硅纳米点阵结构.实验和有限元模拟结果表明,低压压印因为毛细作用下光刻胶在模板内的充分填充可以获得良好的图形复制精度和较小的残余胶厚度,因此适于大面积高密度光刻胶结构的均匀复制.     

Towards high efficiency thin film solar cells

As an alternative to single crystal silicon photovoltaics, thin film solar cells have been extensively explored for miniaturized cost-effective photovoltaic systems. Though the fight to gain efficiency has been severely engaged over the years, the battle is not yet over. In this review, we comb the fields to elucidate the strategies towards high efficiency thin films solar cells and provide pointers for further development. Starting from the photoelectron generation, we look into the fundamental issues in photoelectric conversion processes, including light harvesting and charge handling (separations, transportations and collections). The emerging organic-inorganic halide perovskite systems, as well as the rapidly developed polycrystalline inorganic systems, organic photovoltaics and amorphous silicon cells are discussed in details. The biggest bottleneck for the cost-effective polycrystalline inorganic cells is the composition sensitivity and deep defects; for amorphous silicon cells, it is the quantum of the dangling bonds; for organic cells, it is the low charge carrier mobility and high exciton binding energy; and for perovskite cells, it is the environmental degradation and the controversial mechanisms of generation of I-V hysteresis. Strategies of light harvesting and charge handling as well as directions to break the bottlenecks are pointed out.     

Fabrication of suspended silicon nanowire arrays

A method to fabricate suspended silicon nanowires that are applicable to electronic and electromechanical nanowire devices is reported. The method allows for the wafer-level production of suspended silicon nanowires using anisotropic etching and thermal oxidation of single-crystal silicon. The deviation in width of the silicon nanowire bridges produced using the proposed method is evaluated. The NW field-effect transistor (FET) properties of the device obtained by transferring suspended nanowires are shown to be practical for useful functions.     

Electroluminescent study of the efficiency of silicon heterostructural solar cells

A strong (by more than an order of magnitude) change in the electroluminescence intensity is observed for the first time in high-quality heterojunction solar cells that are based on a single-crystal silicon and have an efficiency of 18 to 20.5%. This effect occurs due to the sharp change in the concentration of the recombination centers on the surface of single-crystal silicon wafers in the course of their pyramidal texturing and also due to the rise in the series resistance. The effect can be used for a quantitative highly sensitive characterization of the texturing, which is a fundamentally important stage in fabricating highly efficient silicon solar cells.     

Increasing the efficiency of polymer solar cells by silicon nanowires

Silicon nanowires have been introduced into P3HT:[60]PCBM solar cells, resulting in hybrid organic/inorganic solar cells. A cell efficiency of 4.2% has been achieved, which is a relative improvement of 10% compared to a reference cell produced without nanowires. This increase in cell performance is possibly due to an enhancement of the electron transport properties imposed by the silicon nanowires. In this paper, we present a novel approach for introducing the nanowires by mixing them into the polymer blend and subsequently coating the polymer/nanowire blend onto a substrate. This new onset may represent a viable pathway to producing nanowire-enhanced polymer solar cells in a reel to reel process.     

Rapid processing of low-cost, high-efficiency silicon solar cells

Rapid and potentially low-cost processing techniques are analyzed and applied toward the fabrication of high-efficiency Si solar cells. (i) A technology that can simultaneously form the phosphorus emitter, boron BSF, andin situ oxide in a single high-temperature furnace step or: simultaneously diffused, textured, and AR coated process (STAR) is presented. (ii) A high quality screen-printed (SP) contact methodology is developed that results in fill factors of 0·785–0·790 on monocrystalline Si. (iii) Aluminum back surface field (Al-BSF) formation is studied in detail to establish the process conditions that result in optimal BSF action. (iv) Screen-printing of Al conductor paste and rapid thermal processing (RTP) are integrated into the BSF procedure, and effective recombination velocities (S _eff) as low as 200 cm/s are demonstrated on 2·3 Ω-cm Si with this rapid thermal processing of screen-printed contacts, Al alloyed BSF processes. (v) A novel passivation scheme consisting of a dielectric stack (plasma silicon nitride on top of a rapid thermal oxide) is developed to reduce the surface recombination velocity (S) to ≈ 10 cm/s at the 1·3 Ω-cm Si surface. The important feature of this stack passivation scheme is its ability to withstand a high-temperature anneal (700–850°C) without degradation in surface recombination velocity. This feature is critical for most current commercial processes that utilize SP contact firing. (vi) Finally, the individual processes are integrated to form high-efficiency, manufacturable devices. Solar cell efficiencies of 17% and >19% are achieved on FZ Si with SP and evaporated (photolithography) contacts, respectively.     

Thin-film polycrystalline silicon solar cells formed by flash lamp annealing of a-Si films

We have fabricated thin-film solar cells using polycrystalline silicon (poly-Si) films formed by flash lamp annealing (FLA) of 4.5-µm-thick amorphous Si (a-Si) films deposited on Cr-coated glass substrates. High-pressure water-vapor annealing (HPWVA) is effective to improve the minority carrier lifetime of poly-Si films up to 10 µs long. Diode and solar cell characteristics can be seen only in the solar cells formed using poly-Si films after HPWVA, indicating the need for defect termination. The actual solar cell operation demonstrated indicates feasibility of using poly-Si films formed through FLA on glass substrates as a thin-film solar cell material.     

纳米多孔硅的电化学制备及性能研究

纳米多孔硅是一种潜在的化学和生物传感材料,本文采用电化学腐蚀法制备纳米多孔硅.采用SEM技术分析多孔硅的表面形貌,研究了腐蚀条件对多孔硅的孔隙率、厚度、Ⅰ-Ⅴ特性的影响.结果表明,多孔硅的孔隙率随着腐蚀电流密度和腐蚀时间的增加而呈线性增大趋势;其厚度随着腐蚀电流密度的增加而近似呈线性增大趋势,随腐蚀时间的成倍增加而显著增大;其Ⅰ-Ⅴ特性表现出非整流的欧姆接触.     

以溶胶-凝胶法PZT薄膜为驱动的微泵研制

采用溶胶-凝胶法(sol-gel)制备技术制作了Pb(Zr,Ti)O3(PZT)压电薄膜,并以PZT薄膜为驱动制作了微泵.采用了V型微阀的微泵主要利用PZT的压电效应.针对微泵的关键结构--复合驱动膜,探索了一种Si/SiO2/Ti/Au/PZT/Cr/Au多层驱动膜结构制备方法,解决了在硅基底上制备PZT薄膜的问题,同时探讨并解决了硅各向异性刻蚀微泵的微驱动腔、单向阀的工艺问题,并通过SEM照片对V型阀和多层驱动膜进行了表征.研究结果表明,采用MEMS技术成功地完成了微驱动器的研制,得到的驱动腔硅杯平坦均匀.在V型阀微泵整体设计中需要的硅片数目少,降低了器件的复杂性,可以满足功耗低、小型化和批量生产的要求.     

新型摇摆质量微陀螺的设计与制作(英文)

首先介绍了两种结构完全对称的高灵敏度的摇摆质量陀螺.设计并制作了一种对角驱动的新型摇摆质量微陀螺.利用硅的各向异性湿法腐蚀等MEMS体加工技术,简化了该微陀螺的制作工艺.该微结构的对称性、一致性和加工精度有很大改善,尤其是振动梁、激励部件和敏感部件等关键部件.详细阐述了该微陀螺的工作原理和结构设计,完成了微陀螺关键部件的制作和样机组装.利用NF公司的FRA 5087频率响应分析仪测试了样机大气下的振动模态,其中驱动频率为5.563 2 kHz,检测频率为5.553 4 kHz,频差为9.8 Hz,小于0.2%.利用频谱分析的方法测试了样机的哥氏力.测试结果表明这种摇摆质量微陀螺的设计与制作方法是可行的.     

Spectra of polycrystalline and single-crystal silicon for solar cells measured by deep-level transient spectroscopy

Investigations are reported concerning the spectra of polycrystalline and single-crystal silicon for solar cells. A broad peak is observed in the distribution of traps in the silicon of commercial solar batteries. It is proposed that they are due to residual impurities. The peaks are suppressed by hydrogen passivation. Pis’ma Zh. Tekh. Fiz. 23, 47–50 (February 26, 1997)     

High efficiency microcrystalline silicon solar cells with Hot-Wire CVD buffer layer

Microcrystalline silicon (μc-Si:H) solar cells with i-layers deposited by hot wire chemical vapor deposition (HWCVD) exhibit higher open circuit voltage and fill factor than the cells with i-layers deposited by plasma enhanced (PE)-CVD. Inserting an intrinsic μc-Si:H p/i buffer layer prepared by HWCVD into PECVD cells nearly eliminates these differences. The influence of buffer layer properties on the performance of μc-Si:H solar cells was investigated. Using such buffer layers allows to apply high deposition rate processes for the μc-Si:H i-layer material yielding a high efficiency of 10.3% for a single junction μc-Si:H solar cell.     

Aluminium doped zinc oxide sputtered from rotatable dual magnetrons for thin film silicon solar cells

This study addresses the electrical and optical properties as well as the surface structure after wet-chemical etching of mid-frequency magnetron sputtered aluminium doped zinc oxide (ZnO:Al) films on glass substrates from rotatable ceramic targets. Etching of an as-deposited ZnO:Al film in acid leads to rough surfaces with various feature sizes. The influence of working pressure and substrate temperature on the surface topography after etching was investigated. It was found that the growth model which Kluth et al. applied to films sputtered in radio frequency mode from planar ceramic target can be transferred to film growth from tube target. Furthermore, the influence of Ar gas flow and discharge power on the film properties was investigated. We achieved low resistivity of about 5.4 × 10^− 4 Ω·cm at high growth rates of 120 nm·m/min. Finally, surface textured ZnO:Al films were applied as substrates for microcrystalline silicon solar cells and high efficiencies of up to 8.49% were obtained.     

Ordered polycrystalline thin films for high performance CdTe/CdS solar cells

An ordered polycrystalline approach is proposed to overcome fundamental problems associated with random polycrystalline thin films, namely grain boundaries and inhomogeneity. The approach consists of two main steps: (1) the deposition of a patterned growth mask and (2) the selective-area deposition of the ordered polycrystals. The ordered polycrystalline approach was investigated using the CdTe/CdS material system. Experimental results demonstrate that SiO₂ and Si₃N₄ are effective growth masks and that temperature is a dominant parameter for selective-area deposition. PL and XRD characterization indicates that the ordered polycrystalline technique has the potential for improving the crystal quality and order of polycrystalline CdTe thin films. The approach appears to be fairly general and could be applied to other material systems.