【作者】 魏铭；

【导师】 朱长飞；

【作者基本信息】 中国科学技术大学 ， 材料物理与化学， 2014， 博士

【摘要】 目前化石燃料仍然是当今人类社会能源的主要来源。但是化石燃料的使用同时会释放有害气体造成环境污染,并且这些能源是不可再生能源,随着时间的推移,化石能源将完全消耗,因此寻找一种环保的可再生能源是亟待解决的问题。太阳能是一种储存丰富的可再生能源,其中光伏电池提供了全新的使用太阳能资源的方法,但是生产成本较大一直制约着太阳能电池的大规模应用。如果可以利用更加成熟的制备手段,那么利用太阳能电池产生能量的方式将更加低成本,效率高。Ⅰ2-Ⅱ-Ⅳ-Ⅵ4半导体材料,包括铜锌锡硫,铜锌锡硒以及铜锌锡硫硒,以其元素含量丰富,材料体系稳定的特点在过去的一段时间里在薄膜太阳能电池器件领域内得到了广泛的关注。相比于真空法制备含有五种元素的多元化合物材料中所面临的制备工艺复杂,生产成本较高的缺点和不足,基于纳米颗粒的溶液法可以很好地改善并解决真空法所面临的问题。本论文将阐述基于纳米颗粒的溶液法制备高效率铜锌锡硫硒薄膜太阳能电池器件的过程及研究影响光电转化效率的原因。论文将按照时间顺序论述制备铜锌锡硫纳米颗粒的原理和过程以及铜锌锡硫硒薄膜太阳能电池光电转化效率从零到7.5%的过程,具体地论文将包括以下三个内容：首先,研究了采用热注入法制备形貌和组分可控的铜锌锡硫纳米颗粒。系统研究了前驱体浓度,前驱体种类以及前驱体中金属比例对合成的铜锌锡硫纳米颗粒结构,形貌和组分的影响。采用硫脲为硫源时可以制备出形貌均匀,尺寸分布窄,且具有锌黄锡矿(kesterite)结构的铜锌锡硫纳米颗粒；同时合成的铜锌锡硫纳米颗粒中Cu/Zn+Sn以及Zn/Sn的比例可以分别在0.8到1之间和1.0到1.3之间调控。分析表明硫脲对形成形貌均匀,尺寸分布窄的铜锌锡硫纳米颗粒起着至关重要的作用,在反应过程中硫脲逐渐分解出硫源是其中最主要的原因。而且通过对于不同时间下铜锌锡硫纳米颗粒形貌的表征,表明由于硫脲分子对称结构的影响,铜锌锡硫纳米颗粒只能在一个方向上生长,最终形成均匀的纺锤形状。紫外可见光光谱测试表明在可见光范围内,铜锌锡硫纳米颗粒具有较高的吸收,其光学带隙为1.52eV,是一种适合做太阳能电池器件的吸收材料。其次,论文研究了使用简单的旋涂方法和滴注方法制备铜锌锡硫前驱体薄膜,探索了墨水浓度,旋涂速度对于薄膜厚度的影响,最终采用200mg/ml的墨水通过4次旋涂制备出厚度大约1μm的铜锌锡硫薄膜。为了得到结晶质量较好的吸收层,论文还研究了不同气氛下和不同硒化温度对铜锌锡硫前驱体薄膜结构,组分,光学性质的影响。总结了硒气氛下结晶质量较好的铜锌锡硫硒吸收层是通过最初形成Cu2-xSe而后又完全消失的自发过程形成的。在硒化过程中锡的损失造成了铜锌锡硫硒吸收层中金属比例失配,同时也严重影响铜锌锡硫硒薄膜太阳能电池器件的光电转化效率,只有3.81%；而通过在硒化过程中添加锡粉,可以有效的减少吸收层中金属比例偏离,薄膜电池的光电转化效率得到了显著的提高,达到了7.50%。Mott-Schottky测试方法进一步揭示了较少的缺陷浓度对于高效率薄膜太阳能电池的重要性。最后,论文还阐述了使用热注入法制备出一种新的元素含量丰富的四元化合物材料,铜镁锡硫。XRD, Raman以及TEM结果表明合成的铜镁锡硫纳米颗粒是一种具有锌黄锡矿结构的材料,同时热注入法制备的铜镁锡硫纳米颗粒中没有其它二元或三元化合物杂相。扫描透射电子显微镜中的能量色散光谱仪面扫描方式(STEM-EDS)测试表明合成的纳米颗粒中包含有铜,镁,锡,硫四种元素。紫外可见光光谱测试表明这种新材料的光学带隙为1.63eV,为进一步研究这种材料作为太阳能电池吸收层奠定了基础。更多还原

【Abstract】 The majority of the world’s energy consumption is derived from fossil fuels. However, due to the environmental issues associated with burning fossil fuels and the diminishing availability of these resources, it is necessary for mankind to develop an alternative source of energy that is more sustainable in the long-term. Solar energy resources are vast:more energy hits the earth in one hour than humankind consumes in entire year. Solar cells offer the potential to change the landscape of how we produce and use energy. However, solar cells technologies have only been used to a limited degree in energy production thus far because of high costs. If developed into a mature technology, they present the opportunity of significantly reduce solar energy costs through earth abundant materials, efficient installation, and roll-to-roll production. Ⅰ2-Ⅱ-Ⅳ-Ⅵ4semiconductors, including Cu2ZnSnS4(CZTS), Cu2ZnSnSe4(CZTSe) and the sulfo-selenide Cu2ZnSn(S,Se)4(CZTSSe), have attracted increased attention for the production of low cost thin film solar cells since they mainly consist of earth abundant or readily available elements in recent years. Owing to the processing complexity associated with the vacuum-based fabrication of CZTS(e) thin film photovoltaic cells, non-vacuum solution-processing can overcome these issues due to the inherent processing advantages over conventional vacuum-based processes.The focus of this study is to demonstrate a viable route of fabricating highly efficient thin-film solar cells by ways of nanoparticles based solution-processing. This dissertation is organized in the order of annals describing the synthesis of CZTS nanoparticles, and the means to improve the CZTSSe solar cells efficiency from zero to about7.5%.Firstly, hot-injection method was used for synthesizing a uniformed and composition controllable CZTS nanoparticle. The effects of the precursor concentrations, the kind of precursors, the metal precursor ratio on the morphology and composition of obtained CZTS nanoparticles were systematically investigated. A narrow size distribution, uniformed, and pure Kesterite CZTS nanoparticle can be achieved using the thiourea as the sulfur source, and the Cu/Zn+Sn ratio and Zn/Sn ratio of the fabricated CZTS nanoparticle can be ranged from0.8to1and1.0to1.3, respectively. Thiourea plays a key role in the formation of nanocrystals with uniform shape and narrow size distribution because thiourea will gradually release sulfur into the solution which triggers reactionwithmetal ion and eventually leads to the formation of CZTS. Time-dependent results showed that CZTS nanoparticle with uniform shape was form initially, and CZTS nanopartilces grew in one direction because of the thiourea’s symmetrical structure. UV-vis absorption spectra of the CZTS nanoparticles revealed a strong absorption in the visible light region with a direct band gap of1.52eV which was optimal for solar cell materials.Secondly, spin-coating and drop-cast methods were investigated to obtain the CZTS thin films. The effect of the various concentrated ink and different spin speeds on the thickness of the thin films were investigated using the spin-coating method. A thickness of1μm CZTS thin films was obtained by4times spin-coating using the200mg/ml ink. The influence of the different selenium atmosphere and annealed temperatures on the structure, morphological and optical properties of CZTS thin film were investigated in the sealed quartz tube. It was concluded that an evolution of the initial formation of Cu2-xSe at the surface, and a subsequent extinction completely was performed during the formation of CZTSSe thin films. Sn loss also be observed during the annealing process under Se atmosphere, which has a negative effect on CZTSSe thin film solar cells, only a efficiency of3.8%thin films solar cells was achieved; While adding Sn powders during annealing process could avoid Sn loss and an improved efficiency thin film solar cell with7.50%was obtained at last. Mott-Schottky measurement showed that the higher efficiency solar cells had a lower carrier concentration which was an advantageous case for high efficiency solar cells.Finally, a new earth-abundant element material Cu2MgSnS4had been synthesized by hot-injection methods. X-ray diffraction, Raman spectrum and transmission electron microscopy elucidated as-prepared nanoparticles are Kesterite Cu2MgSnS4without binary compounds coexisting. Scanning transmission electron microscopy energy-dispersive spectroscopy element mapping shows the copper, magnesium, tin, and sulfur elements distributed uniformly in the nanoparticles. The result of the Uv-vis absorption spectra revealed the Cu2MgSnS4nanoparticles have an optical band gap of1.63eV, which is suitable for application in the field of photovoltaic.更多还原