节点文献
太阳电池材料CuInS2薄膜及其纳米棒阵列研究
【作者】 王震东；
【导师】 陈国荣；
【作者基本信息】 复旦大学 ， 物理电子学， 2010， 博士
【摘要】 太阳能是一种可再生清洁能源,其储量巨大,取之不尽,用之不竭,对环境无污染,对它的应用研究已成为今后人类能源发展的主要方向之一。利用光伏效应实现并网发电是太阳能利用的重要形式,而太阳电池是光伏系统的核心,其产量也得到快速发展,过去10年,每年以超过30%的速度增加。但是,与火力发电和水力发电相比,存在发电成本高的问题,要解决这个问题,关键是要降低太阳电池的生产成本和提高电池的光电转换效率。CuInS2(CIS)是一种重要的Ⅰ-Ⅲ-Ⅵ2族半导体化合物材料,由于具有与太阳光谱非常匹配的禁带宽度(1.55 eV),光吸收系数高(>105cm-1),化学稳定性好,低毒性等优点,使其成为非常有潜力的一种太阳电池吸收层材料。从降低薄膜的制备成本方面考虑,近年来,电沉积、喷雾热解、涂覆技术、丝网印刷等非真空、低成本技术得到一定的应用发展。其中,涂覆法和丝网印刷技术都需以黄铜矿相CIS粉末为前驱体,并且单源蒸发和近空间升华法中也使用CIS粉末来制备高质量的CIS薄膜。为此,论文使用真空烧结法,系统地研究了CIS粉末的烧结合成。在CIS薄膜太阳电池的光电转换效率方面,以其为吸收层的太阳电池的理论效率高达27%-32%,而文献报道的光电转化效率却只有12.2%,电池的效率存在很大的提升空间。电池吸收层的纳米化有利于增加吸收层对光的吸收,并且能促进光生载流子的分离和传输,是提高电池效率的有效途径。对于CIS薄膜太阳电池结构,越来越多的研究者使用Mo薄膜作为CIS基薄膜太阳电池的背电极材料,这主要是由于Mo薄膜具有良好的热稳定性、低电阻率以及其在制备过程中易与上层CIS薄膜形成良好的欧姆接触。作为薄膜电池结构中的背电极材料,Mo薄膜性能的好坏直接影响吸收层CIS薄膜的结晶取向、表面形貌及界面性能,进而对电池性能产生重要影响。目前文献报道的转换效率最高的电池也是以Mo薄膜作为底电极的。基于以上所述,论文主要在直流磁控溅射法制备Mo薄膜、真空烧结法合成CIS粉末、单源热蒸发法制备CIS薄膜、固态硫化法制备CIS薄膜和固态硫化法制备新型CIS纳米棒阵列等方面开展研究工作,并取得了一些研究成果。1.改装了一套直流磁控溅射装置,并运用该装置系统地研究了溅射工艺对Mo薄膜的沉积速率、结构、形貌及电学性能的影响。溅射过程中,当基片温度为150℃时,薄膜获得(211)晶面择优取向,而在其它温度条件下,样品则为(110)晶面择优取向。2.以Cu、In、S粉和CuS、In2S3粉为原料,真空烧结合成CIS粉末。球磨Cu In、S粉的混合物为前驱体,在10-1Pa的真空环境下,350℃低温烧结合成黄铜矿相CIS粉末,粉末的颗粒尺寸大约为250nm,适用于涂覆法及单源蒸发法制备CIS薄膜。3.以合成的CIS粉末为原料,采用单源热蒸发技术在钠钙玻璃基片上沉积薄膜,样晶经250℃-450℃退火处理后,获得了高(112)晶面择优取向的CIS薄膜。电学和光学性能测试显示：薄膜的导电类型为N型,禁带宽度为1.50eV。4.以钠钙玻璃为基底,蒸镀Cu/In薄膜,DSC分析显示薄膜合金化时经历两个相变过程,两相变点温度分别为153℃和314℃,进一步的XRD测试表明第一次相变时生成单斜晶系的Cu11In9,第二次相变则生成三斜晶系的Cu7In3。然后分别硫化Cu11In9和Cu7In3前驱膜均能获得P型CIS薄膜,薄膜的禁带宽度分别为1.34eV和1.39eV。其中硫化Cu7In3前驱膜获得的薄膜中还含有少量CuxS二元杂相。另外,以玻璃/Mo为基底比以Mo箔片为基底制备CIS薄膜的结晶性能更优良。5.将固态硫化法应用于新型CIS纳米棒阵列的制备。该结构中纳米棒阵列垂直生长于薄膜之上,组份测试表明薄膜接近CIS的标准化学剂量比。用该结构膜作太阳电池吸收层时,可增加吸收层对光的吸收,促进载流子的分离与传输,从而有望开发出高效太阳电池。另外,论文还就Ⅰ-Ⅲ-Ⅵ2族半导体材料CuInSe2化合物进行了一些研究,真空烧结合成了CuInSe2粉末,使用固态硒化法在Mo箔片上制备了CuInSe2薄膜。总之,论文围绕太阳电池的低成本和高效率,在太阳电池材料CIS粉末、薄膜、纳米棒阵列和Mo薄膜等方面展开研究,并取得了一定的研究成果。
【Abstract】 As a renewable and clean energy, solar energy is a promising replaceable energy to traditional energy and its application research has been one of the main areas in the energy development, owing to its advantages of enormous reserves, inexhaustibility and being friendly to environment. Solar cell, on the base of photovoltaic effect, is an important form of utilization of solar energy. As the core of the photovoltaic systems, solar cell has been produced in large scale over the past 10 years, with an increase of more than 30% annually. However, compared with traditional thermal power generation and hydropower, solar cell has the problem of higher cost. To solve that, the key is to find methods to reduce production cost and improve the conversion efficiency of solar cell.CuInS2 (CIS), an importantⅠ-Ⅲ-Ⅵ2 ternary semiconductor materials, has emerged as one of the promising absorber materials for thin film solar cells, due to its notable advantages of high absorption coefficient, nearly ideal band gap value of 1.55eV, excellent chemical stablility and low toxicity. As the low cost techniques, electrodeposition, spray pyrolysis, paste coating techniques, screen printing and other non-vacuum technologies have recently been extensively applied to the fabrication of CIS absorber layer, while paste coating method and screen printing technologies using the polycrystalline CIS compound as the precursor, and single-source thermal evaporation and close-spaced sublimation method using the CIS powder to prepare high-quality CIS films. Thus, in the paper, it is systematically studied of the homogenized polycrystalline CIS compound sintered at low temperatures, which is crucial to the preparation of CIS thin film sintered from ball-milled precursors on glass substrates at low cost.As we all know, the photoelectric conversion efficiency of the CIS thin film solar cell is up to 27%-32% theoretically, while the highest conversion efficiency reported was only 12.2%, so there is a lot of potential to improve the efficiency of solar cells. On the other hand, the nanostructure of absorbing layer of solar cell can increase the light absorption, and improve the photo-induced carriers separation and transportation as well, which is effective to improve the efficiency of solar cell.Mo thin film is used as the back electrode material of solar cell by more and more researchers, because of its good properties of heat stability, low resistivity and a good ohmic contact between Mo thin film and the upper CIS thin film. Meanwhile, its performances have a direct effect on the crystalline orientation, surface morphology and interfacial properties of CIS thin film prepared exactly on Mo thin film, resulting in a huge impact on the performances of CIS thin film solar cell. Additionally, the solar cell reported with the highest conversion efficiency is also based on Mo thin film as bottom electrode.In this dissertation, the Mo thin films were deposited as the bottom electrode of solar cell by DC magnetron sputtering, while the chalcopyrite CIS powders were synthesized by vacuum sintering at low temperature, and the CIS thin films were prepared by single-source thermal evaporation and solid-state sulfurization method. The new CIS nanorod array thin film was also researched, by means of solid-state sulfurization method. The research results are summarized as follows:1. The obsoleted equipment was refited into a DC magnetron sputtering device, which was used to prepare Mo thin film, and the effects of sputtering conditions on the Mo film deposition rate, structure, morphology and electrical performance were systematically studied. In sputtering process, the Mo thin film was grown with (211) preferred orientation at 150℃, while (110) preferred orientation in other temperature conditions.2.The CIS powder was synthesized by vacuum sintering with both the precursors including Cu、In and S powders, and CuS、In2S3 powders. The chalcopyrite CIS powder was synthesized with ball-milled precursors including Cu, In and S powder in 10-1Pa at low temperature (350℃), with the product exhibiting a grain size of about 250nm, which is suitable for preparing CIS thin film by paste coating and single-source thermal evaporation method.3. The CIS thin film was deposited on soda-lime glass substrate by single-source thermal evaporation technique, with the synthesized CIS powder used as raw material. After annealing at 250℃-450℃the sample exhibited a (112) preferred orientation, with N type conductivity and a band gap of 1.50 eV.4.The evaporated Cu/In thin films on soda-lime glass had two phase transformations at 153℃and 314℃, confirmed by DSC test, and it was concluded that the monoclinic Cu11In9 and triclinic Cu7ln3 alloys were formed by XRD characterization, respectively. With further solid-state sulfurization, the two alloys were transformed to CIS thin films, which had P type conductivity and band gaps of 1.34eV and 1.39eV, respectively. However, the CIS thin film sulfurized from the precursor of Cu7ln3 alloy also contained a small amount of CuxS binary phase. In addition, the CIS thin film deposited on the glass/Mo substrate had better crystallization properties than that on the Mo foil substrate.5. The new CIS nanorod array thin film was prepared by the solid-state sulfurization method. It can be observed that the CIS nanorod arrays were grown vertically on the thin film by SEM, and the sample was near stoichiometric amount of CIS compound by EDS. The nanostructure of absorbing layer of solar cell is used to increase the absorption for light and improve the photo-induced carriers separation and transportation, which is an effective way to improve the efficiency of the solar cell.Besides, we have studied another importantⅠ-Ⅲ-Ⅵ2 group semiconductor material, CuInSe2 compound. The CuInSe2 powder was synthesized by the vacuum sintering method, and the thin film was deposited on the Mo foil substrate by the solid-state selenization method.In short, in this dissertation, we focus on the fabrication of solar cells with high efficiency and low cost. Many researches were performed on the preparation of CIS powders, thin film and new nanorod arrays thin film, as well as Mo thin film, with a certain amount of research achievement.