基于石墨烯和TMDC的两类范德华异质结构材料光伏特性及其外部调控的研究

New photovoltaic conversion technology based on nanomaterials is an important way to obtain renewable energy. On dealing with the problems such as difficult to prepare , high cost and low efficiency, the two-dimensional materials show great potential for their excellent optical and electrical properties. However, a single two-dimensional material has always been difficult to overcome shortcomings. It is possible to obtain a better photovoltaic performance by combining different two-dimensional materials with van der Waals force to form a heterostructure, which can greatly improve the photovoltaic conversion efficiency. This project will focus on two types of van der Waals heterostructures composed of semiconductor transition metal dichalcogenide and graphene, and study basic electronic, optical and transport properties by theoretical calculation and simulation. The photovoltaic response and I-V characteristics of the materials will be clarified. The important physical laws will be revealed in photovoltaic conversion process such as light absorption, carrier excitation, electron-hole pairs separation and carriers migration. Moreover, the modulation mechanism of the grid voltage, the external strain and doping on the above physical laws and the photovoltaic properties of the material is further studied, to explain and guide the experiment. Finally, the effective methods to improve the efficiency of photovoltaic conversion are expounded from the theoretical level, which lays a solid theoretical foundation for the application of two-dimensional materials in the field of photovoltaic devices.

依赖于纳米材料的新型光伏转换技术是获得可再生能源的重要途径。在应对纳米光伏器件制备难、成本高、效率低等问题时，二维材料以其优异的光学和电学性质展现出巨大的应用潜力。但是单一的二维材料总有难以克服的缺点，而将不同的二维材料以范德华力联结在一起形成异质结构可以获得更好的光伏特性，从而大大提高光伏转换效率。本项目针对半导体性过渡金属硫族化物和石墨烯组成的两类范德华异质结构，利用理论模拟计算的方法研究其基本的电子学、光学和输运性质，阐明材料的光伏响应和I-V特性，揭示光吸收、载流子的激发、电子-空穴对的分离、载流子迁移等光伏转换过程中的重要物理规律。进而深入研究栅极电压、外部应变和掺杂等调控手段对上述物理规律和材料光伏特性的调控机制，达到解释并指导实验的目的。最终从理论的层面阐明提高光伏转换效率的有效方法，为二维材料在光伏器件领域的应用奠定坚实的理论基础。

依赖于纳米材料的新型光伏转换技术是获得可再生能源的重要途径。在应对纳米光伏器件制备难、成本高、效率低等问题时，二维材料以其优异的光学和电学性质展现出巨大的应用潜力。但是单一的二维材料总有难以克服的缺点，而将不同的二维材料以范德华力联结在一起形成异质结构可以获得更好的光伏特性，从而大大提高光伏转换效率。. 本项目针对半导体性过渡金属硫族化物MoS2和石墨烯Graphene组成的范德华异质结构，首先使用考虑了自旋轨道耦合的GW计算方法纠正了二维MoS2/Graphene异质结构的能带，并发现电子极易由MoS2向Graphene转移。而在外加正向偏压或者n型掺杂石墨烯时可以显著减小肖特基势垒高度，更利于电子的转移；反之，在反向偏压足够大或者p型掺杂石墨烯时，电子也可以实现迁移反转。其次利用GW和BSE的计算方法研究了二维MoS2/Graphene异质结构的光学性质，获得了其吸收光谱，发现吸收峰主要由MoS2贡献，但是由于层间作用吸收峰明显变缓。再次利用MD方法研究了螺旋石墨烯条带的弹性性能，发现它具有超强延展性和可逆性。. 通过对MoS2/Graphene异质结构电子和光学性质的研究，我们发现对石墨烯条带进行n型掺杂可以模拟光垂直照射异质结构产生的效应，增大n型掺杂的浓度相当于增大光照强度，可以促进电子-空穴对的分离，同时提高石墨烯的费米能级和降低层间肖特基势垒高度，导致很高的光电导增益效果。这为二维Graphene/TMDC异质材料在光伏器件方面的应用提供了一定的理论支持。