Zn2SnO4基复合电极及其染料敏化太阳能电池光生电荷分离机制与光电性质研究

The dye-sensitized solar cells (DSCCs) based on Zn2SnO4 have many superior characteristics than TiO2 cells, such as larger open-circuit voltage and fill factor,stronger photostability,lower recombination rate of photogenarated charges, etc.. Zn2SnO4 as anode has been applied to the study and exploitation for DSSCs, but the photoelectric conversion efficiency is relative low. Under the energy level matching, we plan to adopt the sol-gel, megnetron sputtering and other methods to prepare disordered compound and ordered compound multilayer films electrode with Zn2SnO4 and other inorganic materials, as well as DSCCs. Utilizing the surface photovoltage spectroscopy (incuding steady state, transient and electric-field induced), the photoelectric and quantum efficiency test system of solar cells, and so forth, we intend to study the photovoltage response and photoelectic conversion efficency and other characteristics for the two structure electrodes and their dye-sensitized solar cells. Firstly, we will analyze comparatively the inherent effect factors and separation mechanism of the separation of photogenerated charges for two composite electrodes and establish the physical mechanism and the model of energy band for the separation of photogenerated charges. Secondly, we will also discuss how the energy level matching between the excited state of dye and the energy level of composite electrode brings the influence and function mechanism of the photogenerated charges separation and photoelectric conversion efficiency, and so on, for DSSCs. Then we will explore the scientific method for enhancing the photoelectric conversion efficiency of DSSCs. Finally, we hope to provide the basis of experiment and theory for the preparation of composite electrode, the research and exploitation of DSSCs with high photoelectric conversion efficiency.

Zn2SnO4基与标准TiO2基染料敏化太阳能电池相比具有较大开路电压和填充因子、较强光稳定性、较低光生电荷复合率等优越特性，作为工作电极已应用于染料电池的研究与开发,但光电转换效率相对较低。本项目拟采用溶胶-凝胶和磁控溅射等方法，在满足能级匹配条件下，把Zn2SnO4和所选无机材料制备成无序复合和有序复合两类多层膜电极，并用染料进行敏化。运用表面光电压谱（含稳态、瞬态和场诱导）、太阳能电池光电和量子效率测试系统等手段，系统研究两类结构电极及其染料电池光伏响应和光电转换效率等特性。首先，对比分析两类复合电极光生电荷分离的内在影响因素和分离机制，建立光生电荷分离的物理机制和能带模型；其次，探讨染料激发态与复合电极间能级匹配对染料电池光生电荷分离、光电转换效率等的影响与作用机制，探索提高染料电池光电转换效率的科学方法，为复合电极制备、高光电转换效率染料电池的研究与开发提供实验和理论依据。

太阳能电池是大规模利用太阳能的重要技术基础，发展太阳能是缓解经济发展与能源及环境之间矛盾的“绿色”新技术，如何降低制备成本、提高光电转换效率是实现太阳能电池快速商业化的关键途径，其中光生载流子的产生、分离和有效收集是提高太阳能电池光电转换效率的关键因素。首先，基于WO3、 a-Bi2O3、TiO2、SnO2与ZnFe2O4四种复合体系，发现能级匹配是实现光生载流子分离的根本要素，然而能级匹配呈现出一定的方向选择性和"反区域效应"，其中"反区域效应"在促进光生载流子有效分离方面起着重要作用。其次，针对In2O3、ZnO、TiO2、 SnO2四种电极材料与Cu4Bi4S9(CBS)纳米带构成的异质结太阳能电池，同样发现能级匹配和“反区域效应”是实现光生电荷高效分离的关键因素。此外，基于ZnO不同微结构构成的ZnO/CBS和ZnO/In2O3/CBS两类异质结太阳能电池，发现ZnO薄膜比表面积、有序传输通道、结晶质量以及In2O3缓冲层等因素的综合作用可以促进光生电荷的有效分离、传输和收集，其中最高光电转换效率可达6.8%。基于上述研究基础，实验中所选择CBS纳米带电子给体虽具有较宽光吸收(300-1400 nm)，但单一CBS薄膜却呈现出较高的光生电荷复合率，研究发现将石墨烯与CBS纳米带复合之后可大大提高光生电荷分离效率。由不锈钢滤网上Zn2SnO4(ZTO)不同微结构、CBS与石墨烯复合体系构成的异质结太阳能电池(ZTO/CBS-RGO)，发现ZTO纳米棒异质结太阳能电池最高光电转换效率为3.0%；石墨烯与CBS纳米带间丰富界面可有效促进光生电荷分离，石墨烯极高电子迁移率也可以提高光生电子收集效率。由于该类太阳能电池呈现出非常好的柔韧性，为探索基于不锈钢滤网固态、柔性太阳能电池提供了重要实验依据。课题组其他成员在Fe掺杂立方相SiC纳米线、Bi4Ti3O12/BiFeO3异质结构以及(Cu2Sn)x/3Zn1-xS纳米颗粒敏化TiO2纳米管等方面也取得了一些研究成果。课题组系列研究成果在提高光生载流子的分离、传输和收集效率以及太阳能电池光电转换效率方面进行了有益探索，为促进固态异质结太阳能电池快速商业化积累了一定的实验和理论基础。