低维材料光电性质的第一性原理研究

The physical problem and practical application in the absorption and transformation of solar energy has become a hot topic in current research. The traditional silicon-based photoelectric technology still dominates the industry market, while its market share in the global energy consumption is only 2-3 percents, limited by expensive price and low transformation efficiency. Low-dimensional material has the advantage of high specific surface area, and some new systems, such as one-dimensional nanotube/wire, two-dimensional graphene, have super-high mobility and mature production engineering, which makes them the most potential candidate of the new photoelectric material. From the angle of theoretical physics, the microscopic mechanism of photoelectric conversion is lack of sufficient physical explanation, and the essential factor behaving as the bottleneck of the transformation efficiency has no quantitative description. The first-principle method provides a powerful tool in this field. We plan to implement a code based on the GW+BSE method, and use it to investigate the ground state electronic structure and the spectrum renormalization due to the optical excitation, consequently to calculate the absorption spectrum of the material. Further, we will apply the self-implemented code for photocurrent calculation to study the photoelectric response in the transport systems of different materials and structures, also the influence of the eigen electronic structure and interfacial states to the photoelectric conversion process will be investigated. Through the analysis of the calculation results, we will try to find out the new solar cell structure with relatively high photoelectric conversion efficiency.

光能的吸收和转换过程中的物理问题以及实际应用已经成为研究热点。工业上，传统的硅基光电技术仍处于主流地位，因其造价昂贵和转换效率低使得光电在当前全球能耗中仅占2-3%。低维材料具有比表面积大，光吸收充分的优点，新兴的低维材料，如一维的纳米管/线， 二维的石墨烯等，生产工艺日趋成熟，超高的迁移率也使得它们成为最有潜力的新一代光电材料。从理论的角度而言，光电转换的微观机制仍缺乏充分的物理解释，限制转换效率的本质因素也没有定量的描述。第一性原理的方法则在这方面提供了一个强有力的工具。我们拟自行开发以GW+BSE方法为主要模块的代码，来研究材料基态的电子结构以及由于光激发带来的能态重整，获得材料的光吸收谱，再结合已有的同为自行开发计算光电流的代码，研究在输运体系中，不同材料结构的光电响应，其本征的电子结构以及界面态对光电转换的过程的影响。通过计算分析，试图寻找具有较高光电转换效率的新型太阳能电池。

具有有限原子层厚度的低维材料具有大的表面积体积比，而且在某些体系中体现出非常高的电子输运迁移率，是作为光电材料的理想选择。本项目拟通过第一性原理的方法，计算低维材料的电子结构以及输运性质，包括在光照条件下的物理参数，从而分析材料的各方面配置对光电转化过程以及转化效率的影响。我们开发了一套结合非平衡格林函数和多体微扰理论的计算程序，可以计算几百个原子大小的体系的电子结构以及光电流等输运性质。多体微扰理论部分应用于分子系列和半导体测试集得到了比较理想的带隙值。将此程序用于分子结、碳纳米管和过渡组元素二硫化物等体系进行了电子结构和输运性质的计算，得到的理论数据和一些实验的对照取得了合理的结果。本项目对光照条件下材料的物性的理论预测进行了初步的尝试，为进一步的理论和实验的对照研究从而达到计算部分替代实验的目标打下基础。