柔性CZTSSe薄膜的应力与掺杂调控及其太阳能电池的性能研究

Cu2ZnSn(S,Se)4 (CZTSSe) thin film has advantages of large optical absorption coefficient and low price for its resource. It will have a wide potential application if a flexible solar cell could be fabricated from it. In this proposal, RF magnetron sputtering will be used to deposit transition layers with different coefficients of thermal expansion and Mo electrode layer as well as three sulphide precursors on flexible Ti foil substrate, and selenizlation will be performed to obtain flexible CZTSSe thin films. By changing surface microstructure of the Ti foil substrate, element and thickness of the transition layer, the effect of interface stress and diffusion of the transition layer element will be explored on its influence on the property of the flexible CZTSSe thin films. On the basis of analysis of structural and morphological properties, photocurrent response spectrum, photoluminescence spectrum and temperature dependent Hall effect measurement will be used to analyze electrical and optical characteristics in the flexible CZTSSe thin films. The mechanism of regulation and control of stress and doping will be explored and a materials physical model will be set up. A flexible CZTSSe/CdS hetero-junction solar cell will be constructed. For the large stress and bending damage issues in the flexible CZTSSe thin films, the origin of them and improvement method will be studied by combination of simulation and experimental measurement. Finally, by establishing a solar cell physical model, the relationship between stress and solar cell performance in the flexible solar cell will be clarified. The achievements of this project will offer experimental basis and theoretical instruction for the development of new type high efficient flexible thin film solar cells with abundant resources.

Cu2ZnSn(S,Se)4 (CZTSSe)薄膜具有光吸收系数大和原料成本低的特点，做成柔性太阳能电池具有广阔的应用前景。拟用磁控溅射在柔性Ti箔衬底上沉积不同热膨胀系数的过渡层、Mo电极层和三种硫化物预制层，再硒化形成柔性CZTSSe薄膜。通过改变Ti箔表面微结构、过渡层元素与厚度，探索界面应力和过渡层元素扩散掺杂对柔性CZTSSe薄膜性能的影响；在结构和形貌分析的基础上，用光电流响应谱、光致发光谱和变温霍尔效应分析柔性CZTSSe薄膜中的电学和光学性能，探究应力与掺杂调控机制并提出材料物理模型；构建柔性CZTSSe/CdS异质结太阳能电池；针对柔性CZTSSe薄膜中的应力大和弯曲损伤等问题，用计算模拟和实验测量相结合方法探索其产生原因与改善措施；建立太阳能电池的物理模型，阐明柔性太阳能电池中应力与电池特性的关联机制，为发展新型高效且资源丰富的柔性薄膜太阳能电池提供实验基础和指导思路。

为了解决柔性CZTSSe薄膜中残余应力对其太阳能电池性能的影响问题，采用ANSYS有限元分析软件对“柔性Ti衬底/过渡Ge层/Mo电极层/CZTSSe”结构的应力分布进行模拟计算，发现过渡Ge层的插入可以有效缓解由于热膨胀系数差异较大所产生的热应力。首先在CZTSSe薄膜中引入双Ge层，即Ge过渡层和Ge掺杂层。发现Ge过渡层的引入可以有效减小CZTSSe薄膜中的残余应力，增加薄膜与衬底的结合力，且Ge过渡层不会在硒化的过程中穿越Mo层扩散至CZTSSe吸收层中。Ge掺杂层可以有效解决CZTSSe与CdS缓冲层能带不匹配的问题。最终在双Ge层的引入下制备得到的柔性CZTSSe薄膜太阳能电池的转换效率提升至3.19%。. 在背电极Mo层与CZTS金属预制层中间采用电子束蒸发法制备了Sb薄膜并提出了Sb掺杂时CZTSSe薄膜的生长机理模型。发现当Sb薄膜的厚度为20 nm时，CZTSSe薄膜的静电势波动值从115.9 meV减小至60.7 meV。采用Sb2Se3薄膜掺杂层制备得到的柔性CZTSSe薄膜太阳能电池表现出最好的光电性能，其转换效率达到4.0%。. 采用在预制层中引入CdS薄膜的方法来完成Cd对Zn的替代，进而抑制CuZn反位缺陷的产生。发现Cd元素的引入可以有效促进CZTSSe薄膜晶粒的生长，改善CZTSSe薄膜与缓冲层CdS之间的能带匹配现象。当CdS位于预制层之上时，Cd元素在吸收层体内分布比较均匀。CdS薄膜的厚度为50 nm时可以获得最佳光电性能的柔性CZTSSe薄膜太阳能电池，其最高转换效率达到4.41%。. 发展了一种简单有效的Na掺杂制备柔性CZTS薄膜太阳能电池的方法。将一定浓度比例的NaCL, CH₃COONa和Na₂S₂O₃的水溶液滴涂在CZTS前驱体薄膜的顶部，高温硫化后发现相比于不掺Na的薄膜样品，采用Na₂S₂O₃引入Na掺杂的方法能够获得结晶质量最高，表面更为均匀致密的CZTS薄膜。当Na₂S₂O₃的掺杂浓度为0.05mmoL/mL时，基于此前驱体薄膜制备的柔性CZTS太阳能电池的光电转换效率达到了5.83%。