铜锌锡硫硒薄膜太阳电池的微区缺陷与超快载流子动力学研究

Cu2ZnSn(S,Se)4 (CZTSSe) is recently considered as one of most promising candidates of film solar cell with high efficiency and low cost. However, short minority -carrier lifetime and open voltage deficit caused by large amounts of lattice defects are regarded as the main limit of the efficiency of solar cell. There is still a lack of understanding the defect properties and ultrafast carrier dynamics in CZTSSe film because that the macro-scale methods of characterization does not provide insight into the microscopic defect. Thus, the micro-area ultrafast spectroscopy is highly expected to understand the relation between defects and the ultrafast carrier dynamical mechanisms in CZTSSe film. In the project, we are planning to develop a micro-area spectroscopy method with high time and space resolution by combining the confocal microscopy and ultrafast spectroscopy, and study the ultrafast carrier dynamics of CZTSSe solar cell. Combining the wavelength selection, and defect controlling techniques, we will measure the lifetime of carrier thermalization and recombination in the different position of film (bulk, surface, heterojunction interface, and grain boundary). Deep level transient spectroscopy (DLTS) is also used to measure the energy positions and concentrations of defects. Comprehensive comparative analysis is helpful to reveal the direct relation between the various defect states and ultrafast carrier dynamics, and understand the physical mechanisms of short minority- carrier lifetime and low efficiency of solar cell. These researches are expected to be helpful to the material preparation and device design and fabrication of CZTSSe solar cell.

铜锌锡硫硒（CZTSSe）是最近兴起的高效低成本薄膜太阳电池理想候选材料之一。然而由于大量晶格缺陷的存在导致少子寿命过短和开路电压损失过大，制约了电池效率的提高。由于宏观表征技术难以提供缺陷微观信息，人们对缺陷性质和载流子动力学机制还缺乏深入理解。因此，发展微区超快光谱分析方法无疑将对我们理解材料缺陷与载流子动力学机制之间的联系具有重要意义。本项目拟将共聚焦技术和超快光谱相结合，发展同时具有高时间和空间分辨率的微区超快光谱技术，开展CZTSSe薄膜电池的微区载流子动力学研究。结合波长选择和缺陷控制材料制备技术，测量薄膜体内、表面、异质界面和晶界处的载流子热化时间和少子寿命；同时利用深能级瞬态谱测量缺陷的能级位置和浓度等参数；通过综合分析揭示薄膜中的深浅缺陷和载流子动力学机制之间的直接联系，深入理解影响少子寿命和电池效率的物理机制，从而为高效CZTSSe薄膜电池的材料和器件制备提供有益思路。

铜锌锡硫硒（CZTSSe）吸收层和界面缺陷是导致开路电压损失，制约电池效率提高的重要原因。本项目主要在CZTSSe薄膜生长及电池制备；材料中的缺陷性质和载流子动力学机制等方面开展了系统的研究，取得了如下研究成果：（1）掌握了高质量CZTSSe 吸收层和界面的制备方法。系统研究了不同阴离子和不同价态Cu源对CZTSSe吸收层和电池性能的影响。提出了将短时高温硫化与添加SnS粉末相结合的新工艺，实现了CZTS大晶粒生长。通过比较溅射和CBD法制备的CdS缓冲层的物性，提出基于CBD-CdS扩散和阻塞的模型，揭示了Voc损失降低、Rsh升高的内在机理。通过在硒化过程中引入SnSe和SnS粉末，发现Sn蒸汽使CZTSSe吸收层和Mo/CZTSSe界面的空洞显著减少，同时有效降低Mo(S,Se)2层厚度。（2）利用溅射法和溶液法成功制备了高效率CZTS和CZTSSe薄膜电池（>11%）。研制了基于CZTS/CdS异质结的高性能自供电垂直结构光探测器。（3）自建了共聚焦微区超快光谱系统，结合导纳谱和DLTS等电学表征技术，研究了CZTSSe和InGaN等新型薄膜电池材料的缺陷性质及其对载流子动力学的影响机制。结合光谱分析和缺陷计算，我们认为CZTS的带尾态主要来源于高浓度的[2CuZn+SnZn]缺陷簇，而深施主态来源于SnZn。观察到CZTS中深能级的载流子冻析效应导致低温低功率下探测器的电容等响应的反常行为。发现采用四元前驱体制备CZTSSe，可抑制二次相和CuSn缺陷的形成，提高有利浅缺陷VCu浓度。已在Solar Energy，J. Alloys Compds., J. Phys. Chem. Lett.等国内外SCI期刊上发表22篇学术论文。申请并获得国家发明专利授权1项。