Cu2ZnSnS4薄膜成分-结构-性能关系的理论模拟与电化学方法的可控制备

Cu2ZnSnS4 film materials receive wide attention because of their abundant element resources and suitable energy band structure for the absorption layer of solar cells. But their existing preparation methods, such as vacuum deposition, sol-gel method, successive ionic layer adsorption and reaction, have many problems such as complex equipment and technique, high cost and long period of preparation, and confined size, etc. In this project, Cu2ZnSnS4 films will be prepared with electrochemical method. The intrinsic relationships between the composition, structure factors (such as the stability of the pure phase, species and content of point defects, grain size), and energy band structure and other photovoltaic properties of Cu2ZnSnS4 films will be researched based on theoretical calculations, in the light of the crucial factors of property optimization, such as the control of compositon and structure. Universal principles of the structure design and optimization of the films will be advanced. On such basis, the electrolyte composition will be optimized by the selection of the complexing agents and buffer agents according to coordination chemistry theory. The electrochemical parameters of the electrodeposition process will be adjusted. One-step electrodeposition preparation and composition control of Cu2ZnSnS4 films will be achieved by the electrolyte design and the parameter adjustment. The precise structure control of the films with non-stoichiometric composition will be achieved by the further annealing with different extent according to the calculation results, phase diagrams and themodynamic function data of different phases, so as to achieve targeted control of photovoltaic properties of the films. Heterojunction with Cu2ZnSnS4 films will be further prepared to research the feasibility of their controllable electrochemical preparation through the actual promotion of the photoelectric transformation efficiency.

Cu2ZnSnS4薄膜因元素资源丰富、能带结构适用于太阳能电池的吸收层受到广泛关注。但现有真空沉积、溶胶-凝胶、连续离子层吸附反应等制备方法存在设备、工艺复杂、制备成本高、周期长、尺寸受限等问题。本项目采用电化学方法制备Cu2ZnSnS4薄膜，针对其成分、结构调控等性能优化的关键因素，基于理论计算研究薄膜成分、纯相稳定性、点缺陷种类和浓度、晶粒尺寸等结构因素与薄膜能带结构等光电性质的内在关系，提出薄膜结构设计优化的普适性原则。在此基础上，基于配位化学理论选择络合剂和缓冲剂，优化电解液组成，调节电沉积过程的电化学参数，实现其一步法电沉积制备和成分调控。进而基于计算结果、相图和薄膜中各相的热力学函数值等对非化学计量比成分的薄膜进行不同程度的退火，实现其结构的精确调控，从而实现其光电性能的针对性调控。进行Cu2ZnSnS4薄膜异质结的组装，从光电转换效率的实际提高研究薄膜电化学可控制备的可行性。

Cu2ZnSnS4(CZTS)薄膜因元素资源丰富、能带结构适用于太阳能电池的吸收层，被认为是代替Cu(In, Ga)Se2的理想材料。其多元素的组成提供了丰富的性能变化空间。但其成分-结构-性能的关系的复杂性使其性能提高受到限制，现有有真空沉积、溶胶-凝胶、连续离子层吸附反应等制备方法存在设备、工艺复杂、制备成本高、周期长、尺寸受限等问题。本项目采用电化学方法制备CZTS 薄膜解决薄膜制备的困难，针对其成分、结构调控等性能优化的关键因素，基于理论计算研究薄膜成分、纯相稳定性、点缺陷、晶粒尺寸等结构因素与薄膜能带结构、载流子类型、浓度、迁移率等光电性质的内在关系，提出薄膜结构设计优化的普适性原则。在此基础上，基于配位化学理论选择络合剂和缓冲剂，优化电解液组成和电解工艺，调节CZTS薄膜的结构与性能。取得的主要成果如下：(1)基于第一性原理和经验电子理论，通过体系形成能的计算结果，给出了铜锌锡硫合金能够保持锌黄锡矿纯相的理论成分变化范围，通过能带结构等计算阐明了铜锌锡硫纯相成分变化与载流子迁移率、载流子浓度等电学性能的关系，提出了CZTS合金太阳能电池吸收层成分设计的原则并得到了实验印证；(2)通过对电解液中元素络合、电沉积过程中的电化学过程的研究，揭示了CZTS薄膜一步电沉积机理，实现了预沉积薄膜预期成分的精确调控，并提出了电解液的设计原则；(3)依据所提出的原则设计了一种新型电解液，实现了一步电沉积薄膜成分接近化学计量比，省去了随后的硫化过程，有利于环保；(4)通过热处理方法的设计调控CZTS薄膜的结构，同时实现了高载流子浓度和高载流子迁移率，并揭示了这种双高的性能与薄膜结构的关系，为性能提高提供了理论指导；(5)用不同的一步电沉积CZTS薄膜组装了太阳能电池，揭示了吸收层结构和性能对电池效率的影响。这些结果对CZTS薄膜及相应太阳能电池的工业化具有指导意义。