铜锌锡硫硒（Cu2ZnSn(SxSe1-x)4，CZTSSe）薄膜太阳电池具有性能稳定、环境友好、原料丰度大、生产成本低等一系列优点，是一种有很大潜力的光伏器件。在CZTSSe吸收层制备工艺中，溅射CZTS靶材后硒化退火工艺适合制备大面积均匀性良好的薄膜，并且工艺流程简单，有利于CZTSSe电池组件的规模产业化生产。本文基于溅射CZTS四元陶瓷靶材后硒化工艺，系统性研究CZTSSe吸收层的成分和组织；考察了退火工艺对低带尾态CZTSSe电池的影响；通过碱金属Cs原位掺杂提高电池效率，并提出Cs掺杂抑制吸收层中带电缺陷的作用机理。主要研究内容和成果如下：研究了Cu/(Zn+Sn)和Zn/Sn对CZTSSe吸收层及电池性能的影响。发现吸收层中Cu/(Zn+Sn)的提高导致了载流子浓度的升高和二次相Cu3Se2的出现，Zn/Sn的提高引起了吸收层结晶性的下降和二次相ZnSe的产生，均对电池效率产生了危害。性能最佳的CZTSSe电池对应的靶材成分为Cu/(Zn+Sn)=0.7和Zn/Sn=1.1。研究了H2Se浓度对CZTSSe吸收层形貌和物相转变的影响。发现提高H2Se浓度可抑制CZTSSe的分解和二次相的产生，当H2Se浓度为4.5 vol.%时，获得了无孔洞的单相富硒CZTSSe吸收层。提出二步升温工艺消除了CZTSSe/Mo界面处因硒化不充分形成的细晶粒层，获得了形貌、成分均匀分布的CZTSSe吸收层，制备得到了效率为10.19%的CZTSSe电池。研究了CZTSSe在不同退火温度下的晶粒生长和相变情况。发现随着退火温度升高，晶粒尺寸增加，提高了CZTSSe电池效率；但MoSe2层厚度也随之增加，导致了电池效率下降。硒化时四元相CZTS预制膜直接转变为五元相CZTSSe吸收层，降低了二次相和缺陷的产生，在500 ℃下制备得到了具有低带尾态、效率为11.83%的CZTSSe电池。发现Cs掺杂能够降低吸收层中带电缺陷浓度，提出了Cs掺杂抑制CZTSSe中带电缺陷的机理。硒化退火后半径更大的Cs离子倾向于富集在晶界处，由于Cs离子对Na离子的排斥作用，促使更多的Na离子进入CZTSSe晶粒中，占据与Na同价的Cu空位并抑制了ZnCu缺陷的产生。通过在CZTS靶材中原位掺Cs的方法，制备得到了光电转换效率为13.44%的Cs掺杂CZTSSe电池，超过了IBM12.6%的CZTSSe电池世界效率记录。
Copper-zinc-tin-sulfur-selenium (Cu2ZnSn(SxSe1-x)4, CZTSSe) based solar cell is a promising photovoltaic device with great potential because of its stable performance, environmental friendliness, a large abundance of raw materials, and potentially low production costs. In all of the preparation processes for CZTSSe absorbers, the combination of growing CZTS precursor by sputtering CZTS target and then selenization annealing is of the advantages of process simplicity and availableness for large-area uniform thin films. So the process is suitable for the large-scale industrial production of CZTSSe solar cell modules. In the work, the composition and phase structure of CZTSSe absorbers has been systematically studied based on the combination process. The effects of selenization annealing on the performances of CZTSSe solar cell with slight band tailing states has been investigated. The efficiency of CZTSSe solar cells has been improved by in-situ Cs doping. And the mechanism of action, that is, Cs doping could suppress the formation of charged defects in CZTSSe absorbers, has been proposed. The principal research and results are as follows:The effects of Cu/(Zn+Sn) and Zn/Sn on the CZTSSe absorbers and device performances have been investigated. It was found that the increase of Cu/(Zn+Sn) in the absorber leads to the increase of carrier concentration and the appearance of the Cu3Se2 secondary phase. The increase of Zn/Sn might cause the crystallinity deterioration of the absorber and the formation of the ZnSe secondary phase. The crystallinity deterioration and the formation of all these secondary phases result in the damage of device performances. The CZTSSe solar cell with the best performance could be obtained using the CZTS target with a Cu/(Zn+Sn) ratio of 0.7 and a Zn/Sn ratio of 1.1.The influences of H2Se concentration in selenization atmosphere on the morphologies and phase transformations of CZTSSe absorbers have been studied. It was found that the decomposition of CZTSSe and the formation of secondary phases could be suppressed by the increase of H2Se concentration. When the concentration of H2Se in the annealing atmosphere reaches up to 4.5 vol.%, a Se-rich CZTSSe absorber with pure kesterite phase and without holes could be obtained. A novel two-step annealing process was proposed to eliminate the fine-grain layer formed at the absorber bottom adjacent to the CZTSSe/Mo interface on account of insufficient selenization. The CZTSSe absorber with a more homogeneous composition and morphology can be fabricated, and the device with an efficiency of 10.19% was obtained.The grain growth and phase formation of CZTSSe absorbers at different annealing temperatures have been studied. It was found that as the annealing temperature increases, the increase of grain size improves the efficiency of CZTSSe solar cells, but the increase of the thickness of the MoSe2 layer at the CZTSSe /Mo interface leads to a decrease in device efficiency. The quinary phase CZTSSe absorber is directly generated by the selenization of the quaternary phase CZTS precursor in the annealing process, which would reduce the occurrence of secondary phases and defects in the absorber. Finally, a CZTSSe solar cell with slight band tailing states achieves the efficiency of 11.83% fabricated at the annealing temperature of 500 ℃.It has been found that Cs doping could reduce the concentration of charged defects in CZTSSe absorbers, and the mechanism of action has been proposed. Cs doping could suppress charged defects in the absorbers. Cs ions with a larger radius tend to be concentrated at the grain boundary after selenization annealing. Due to the repulsion of Cs ions on Na ions, more Na ions are promoted to enter CZTSSe grains, occupying Cu vacancies and suppressing the generation of ZnCu defects. The CZTSSe solar cell with the highest efficiency of 13.44% in the work has been obtained by in-situ Cs doping in the CZTS target, which exceeded the world efficiency record of 12.6% held by IBM.
