太阳电池新材料新方法

该文叙述了发展低成本，高效率太阳电池光伏有源材料CuIn1-xGaxSe2(CIGS)和新式薄膜电淀积技术的优点，详细报告了该研究项目采用的新式CIGS薄膜电淀积的整个实验制作过程，给出了在香港政府创新科技基金资助下的第一阶段所取得的成果，实验结果已证明：采用这种简单而新颖的电淀积方法能制得光伏用的多晶半导体CIGS薄膜材料，通过测试确定了这种材料具有四方晶体结构，特征峰为（112），（204，220）的多晶CIGS材料，已测得连续分布的薄膜层厚约1．6um，晶粒的平均大小约2um长，具有太阳电池所需的材料质量，实验还 ：此法可重覆生产出厚度和质量相近的CIGS薄膜，该文也做了有关技术 的讨论和分析，这种新式的材料和薄膜技术对生产商品化低成本，高效率薄膜太阳电池无疑是非常有希望的。     

Investigation of rapid thermal annealing on Cu(In,Ga)Se2 films and solar cells

Rapid thermal annealing (RTA), with fast ramp rate, was performed on several Cu(In,Ga)Se₂ (CIGS) films and solar cells under various peak annealing temperatures and holding times. Characterizations were made on CIGS films and cells before and after RTA treatments to study effects of RTA on the CIGS film properties and cell performance. In addition, AMPS-1D device simulation program was used to study effects of defect density on the cell performance by fitting the experimental data of RTA-treated CIGS cells. The results show that RTA treatments under optimal annealing condition can provide significant improvements in the electrical properties of CIGS films and cell performance while preserving the film composition and microstructure morphology.     

氢处理对太阳薄膜材料Mo/CuIn1-x GaxSe2/CdS的影响

将固态源硒化法制备的太阳薄膜材料(Mo／CuIn1-xGaxSe2／Cds)在500℃进行氢处理和氮处理，然后利用XRD、SEM和I-V测试分析了氢处理和氮处理对CuIn1-xGaxSe2薄膜结构、形貌和太阳电池性能的影响。研究表明在500℃的条件下，经过不同时间的氢处理，可以使样品的开启电压减小(特别是经过180min氢处理的样品)，提高了p-n结的性能，从而提高光电转换效率，并可以使样品表面的大颗粒逐渐减少，促进CuIn1-xGaxSe2相的形成，这和I—V性能的测试结果相符合。而氮气的处理对于样品的I—V性能几乎没有影响，这证明了上述性能的提高是由于氢的钝化作用引起的，而非普通的热处理所致。     

周期换向脉冲电沉积-硒化法制备铜铟镓硒薄膜

采用周期换向脉冲电沉积法于Mo/玻璃及ITO/玻璃衬底上制备铜铟镓硒薄膜。Mo/玻璃或ITO/玻璃为工作电极,饱和甘汞(SCE)为参比电极,大面积铂片作为阳极构成三电极体系,以氯化铜,三氯化铟,三氯化镓和亚硒酸的水溶液为电解液,制备Cu-In-Ga-Se合金预制膜,随后在硒蒸气中进行硒化处理,得到了黄铜矿结构的CuInGaSe2(CIGS)薄膜.分别用SEM,XRD和UV-吸收分析了合金预制膜和CuInGaSe2薄膜的表面形貌、相组成及紫外-可见吸收特性。结果表明,周期换向脉冲电沉积法可以制备表面平整、均匀致密的Cu-In-Ga-Se合金薄膜;利用脉冲电压的占空比可以提高预制膜中的In元素的比例,且随着In含量的增加,CIGS薄膜的结晶性变好;适当延长硒化退火的时间,可以使薄膜晶粒大小均匀,减小内应力,使薄膜的光吸收率提高,以利于制备更高效率的CIGS薄膜太阳电池.     

Technological and economical aspects on the influence of reduced Cu(In,Ga)Se2 thickness and Ga grading for co-evaporated Cu(In,Ga)Se2 modules

Reducing the Cu(In,Ga)Se₂ (CIGS) thickness is one way of improving the throughput and capacity in existing production, provided that the efficiency can be kept at a high level. Our experimental results from an in-line co-evaporation process show that it is possible to produce CIGS solar cells with good efficiency at a CIGS thickness of less than 1 μm. An efficiency of 14.4% was obtained for an evaporation time of 8 min and a resulting CIGS thickness of only 0.8 μm. The quantum efficiency measurements show only a minor reduction of the collection in the infrared region that can be related to losses caused by reduced absorption. Passivation of the back contact has been found to be important for thin devices and one way of obtaining good back contact properties, or to reduce the impact of back contact recombination is to use an increased Ga content near the back contact. We have found that Ga grading is feasible also in the three stage process, i.e. a Ga-rich layer near the back contact from stage one is to a high degree retained also after stages two and three. In this paper we discuss the implication of efficiency reduction for the economy of the production and how high efficiency loss that can be tolerated, provided that the output is doubled at equal production cost for the CIGS layer.     

High voltage Cu(In,Ga)S2 solar modules

Sulfurcell (SC) has been running a pilot production for thin-film solar modules using CuInS₂-chalcopyrite (CIS) as absorber material since 2004. Since then production technology has been constantly improved with module power values exceeding 64 W, corresponding to an aperture area efficiency level of about 9%. Small area (0.5 cm2) cells cut out of such CIS modules reach maximum efficiencies close to 11%. Strong efforts have been made to develop a new sequential Cu(In,Ga)S₂ (CIGS) process suitable for production of large-scale CIGS solar modules thereby enabling module efficiencies above 10%. CIGS-based solar cells are—quite similar to CIS-based modules—prepared from sputtered metals subsequently sulfurized using rapid thermal processing in sulfur vapor. Such Cu(In,Ga)S₂ solar cells reach material record efficiencies about 13%. The cells are characterized by high open-circuit voltages up to 890 mV. Based on the results of the “Helmholtz Zentrum Berlin” (HZB), Sulfurcell has successfully scaled this process to our typical module size of 125 cm × 65 cm and is currently piloting the process for mass production. This paper will give an overview of electrical and structural parameters of world's first large-scale CIGS modules. CIGS module and cell parameters will be compared with standard CIS module and cell parameters and measured CIGS efficiency temperature coefficients will be compared with typical temperature coefficients of modules based on established PV technologies.     

Defect levels in CuGaSe2 by modulated photocurrent spectroscopy

Results of high frequency modulated photocurrent spectroscopy (HF MPC) performed on epitaxial and polycrystalline CuGaSe₂ thin films are presented. Frequency and temperature scans of MPC in the high frequency regime are compared, and the advantages of the second mode of measurement over the first one are demonstrated. Electronic parameters of defect levels in Cu-rich and Ga-rich stoichiometry are obtained and discussed in comparison to the literature data on defect levels derived from capacitance junction techniques. An attempt to correlate levels observed by MPC technique with material stoichiometry has been made.     

Thinning of CIGS solar cells: Part I: Chemical processing in acidic bromine solutions

CIGSe absorber was etched in HBr/Br₂/H₂O to prepare defined thicknesses of CIGSe between 2.7 and 0.5 μm. We established a reproducible method of reducing the absorber thickness via chemical etching. We determine the dissolution kinetics rate of CIGSe using trace analysis by graphite furnace atomic absorption spectrometry of Ga and Cu. The roughness of the etching surface decreases during the first 500 nm of the etching to a steady state value of the root-mean-square roughness near 50 nm. X-ray photoelectron spectroscopy analyses demonstrate an etching process occurring with a constant chemical composition of the treated surface acidic bromine solutions provide a controlled chemical thinning process resulting in an almost flat surface and a very low superficial Se⁰ enrichment.     

Composition and bandgap control in Cu(In,Ga)Se2‐based absorbers formed by reaction of metal precursors

The control of composition and bandgap in chalcopyrite thin‐film absorber layers formed by a metal precursor reaction is addressed. Two processes using reaction with either H₂Se or H₂S as the final step of a three‐step reaction process were compared as follows: a three‐step H₂Se/Ar/H₂S reaction and a three‐step H₂Se/Ar/H₂Se reaction. In both processes, significant Ga homogenization was obtained during the second‐step Ar anneal, but the third‐step selenization resulted in Ga depletion near the Cu(InGa)Se₂ surface, whereas the third‐step sulfization did not. Solar cells were fabricated using absorbers formed using each method, and the surface Ga depletion significantly affected device performances. The solar cell incorporating the sulfization yielded a better device performance, with an efficiency of 14.4% (without an anti‐reflection layer) and an open‐circuit voltage of 609 mV. The bandgap control in the metal precursor reaction is discussed in conjunction with the device behavior. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence of Ni and Cr impurities on the electronic properties of Cu(In,Ga)Se2 thin film solar cells

Deposition of Cu(In,Ga)Se₂ (CIGS) thin film solar cells on metallic substrate is an attractive approach for development of low cost solar modules. However, in such devices, special care has to be taken to avoid diffusion of impurities, such as Fe, Ni, and Cr, from the substrate into the active layers. In this work, the influence of Ni and Cr impurities on the electronic properties of CIGS thin film solar cells is investigated in detail. Impurities were introduced into the CIGS layer by diffusion during the CIGS deposition process from a Ni or Cr precursor layer below the Mo electrical back contact. A high temperature and a low temperature CIGS deposition process were applied in order to correlate the changes in the photovoltaic parameters with the amount of impurities diffused into the absorber layer. Solar cells with Ni and Cr impurities show a reduction in the device performance, whereas the effect was most pronounced in Ni containing devices. The presence of deep defect levels in the absorber layer was identified with admittance spectroscopy and can be related to Ni and Cr impurities, which diffused into the CIGS layer according to secondary ion mass spectroscopy depth profiles and inductively coupled plasma mass spectrometry. Copyright © 2014 John Wiley & Sons, Ltd.