纳米金属调控石墨烯/Si异质结太阳电池及其耦合增强机理研究

High-efficiency and low-cost solar cells is the future trend of development. This shows higher demands for the structure and materials. Graphene（GN）/silicon heterojunction solar cell attracted more attentions during the past years due to its simple structure which should be lower cost. In this project, we will deposition graphene films with different layers by plasme-enhanced chemical vapor deposition on Si directly. The metal nano-structure (NS) will be spin-coated on the graphene films. Then, the graphene films made by CVD on Cu or Ni will be transferred on the surface of NS/GN/Si to made the sandwich structure of GN/NS/GN. Studies on the growth kinetics of graphene films by CVD should be done, and we will show the relationship between the growth atmosphere, reaction gases and the film layers. According to the SEM、TEM、transmittance and I-V properties of graphene films, the role of metal nano-structure in graphene films will be studied, include how the microenvironment, the size and dispersity of nano-structure influence the optical and electrical properties of films. The studies on the enhanced light scattering and carrier transportation properties of the graphene composite solar cells will be done to find the function of the metal nano-structure in films. At the same time, we will do some theoretical studies by first-principles calculations. The dielectric constant of the films with metal nano-structure and the state density of the solar cells should be calculated to determine the rules of the light absorbing, carrier electrical properties affected by the metal nano-structure. Finally, a optimized structure of graphene/silicon heterojunction solar cell with a higer efficiency will be shown.

石墨烯具有高的透过率和载流子迁移率，是理想的太阳电池材料。本项目拟设计一种新型石墨烯/Si异质结太阳电池，将纳米金属嵌入石墨烯膜中形成三明治结构，依靠纳米金属结构在材料中的等离子增强作用提高其光吸收特性，同时，利用纳米金属与上下两层石墨烯的相互作用，调控其载流子输运特性，达到提高电池效率的目的。本项目采用化学气相沉积的方法在Si衬底上制备层数可控的石墨烯膜，利用溅射等方法以及石墨烯转移法获得纳米金属复合石墨烯结构。理论与实验相结合，系统研究石墨烯膜层数、金属纳米结构的种类、颗粒尺寸、分散度、存在状态和微环境等对薄膜光电特性的作用规律；阐明石墨烯层数、金属纳米结构对于石墨烯/Si异质结太阳电池光散射及载流子输运特性的耦合增强机制，最终获得高效纳米金属调控石墨烯/Si异质结太阳电池的最佳结构工艺。

作为一种零带隙的半金属材料，石墨烯具有很多优异的性能：单层石墨烯具有可调的功函数及能带结构，入射光透过率高达97.7%，载流子迁移率可达200000 cm2V-1s-1，这些性能使石墨烯有望成为良好的透明导电材料。近年来，利用石墨烯与半导体材料接触形成肖特基结来制备太阳能电池器件引起了人们的广泛兴趣，在此类电池中，石墨烯不仅作为一种透明导电电极，还为电子-空穴对的分离以及空穴的传输起到重要的作用。作为一种新兴的太阳电池，石墨烯/硅异质结太阳电池近几年取得了很大的发展。但与传统的晶硅太阳电池相比效率偏低，原因主要为以下两个方面：（1）石墨烯较低的载流子浓度及偏小的功函数，使得太阳电池的势垒高度低，进而导致开路电压降低。（2）硅片在可见光及红外波段反射率大概能达到30%-40%，影响了太阳能电池对光的吸收。本项目以石墨烯/Si异质结太阳电池为研究对象，通过在石墨烯膜中引入金属纳米结构调控太阳电池的性质，研究这种新型结构的电池特性及纳米金属结构在电池中光电耦合增强的相关问题。在机理研究方面，阐明新型石墨烯/Si异质结太阳电池中石墨烯层数和纳米金属对石墨烯光学和电学特性的耦合作用，澄清纳米金属结构与石墨烯的配置关系对石墨烯/Si异质结太阳电池性能的影响作用。针对石墨烯层的受主浓度、功函数、禁带宽度以及晶硅层施主浓度几个重要的参数，研究了它们对短路电流密度、开路电压、填充因子、效率的影响规律。采用氯化金、金颗粒处理石墨烯/硅异质结太阳电池，获得了纳米金属嵌入的石墨烯/硅异质结太阳电池结构，获得了电池效率的提升，金薄膜的厚度为7.5 nm时，电池的效率最高，为3.42%。并创造性地把PMMA旋涂到石墨烯/硅异质结太阳电池上，起到了减反的作用，最终获得的电池转换效率达到9.64%。 并拓展研究了石墨烯的热电性质，为石墨烯光电热电一体化器件提供了理论基础。