大面积石墨烯/二硫化钼异质结可控生长及在柔性太阳能电池中应用基础研究

Two-dimensional materials, such as graphene, MoS2 etc, with excellent optoelectronic, mechanical and stable properties; and the photoelectric conversion efficiency of the heterostructures was up to 10% via theoretical modeling, would be widely used in the flexible and wearable solar cell. Nevertheless, the transfer process in hand of fabricating heterojunctions results in the residual contamination and damage in the sample and interface, thereby degrades the performance of devices sharply. In addition, the method in effect for direct growth of large-scale, high-quality heterojunctions is still absence. In this project, the controllable method based on the chemical vapor deposition for direct growth of graphene/MoS2 heterojunctions was proposed upon the regulating the surface energy and chemical reactivity of graphene substrate. Its application on flexible solar cell will be studied. The MoS2 film would be effective growth on the graphene substrate by regulating the kinetics and thermodynamic parameters. Upon the growth, the kinetics process and intrinsic mechanism of growth MoS2 film on graphene with a big lattice mismatch will be unfolded. The flexible solar cells are fabricated based on the as-grown large-scale, high-quality heterojunctions. Further, the effect of layered number, stacking way and stress of both graphene and MoS2 on the Schottky barrier height and performance of cell are studied in detail, and a model for atomically layered graphene-MoS2 semiconductors contact will be built. This work will lay the foundation for controllable growth of the heterojunctions and its applications in photovoltaics.

石墨烯及二硫化钼等二维材料具有优异的光电特性、良好的机械性能和稳定性；理论模拟表明由它们组成的异质结光电转换效率可达10%，将在柔性可穿戴式太阳能电池方面广泛应用。然而目前异质结转移制备方式对样品及结界面的污染和破坏，严重降低器件性能；大面积高质量异质结直接生长技术仍然缺乏。本项目基于对石墨烯表面能和反应活性的调节，提出利用化学气相沉积直接可控生长石墨烯/二硫化钼垂直异质结，并将其应用于柔性可穿戴式太阳能电池。通过调控反应动力学和热力学参数，使二硫化钼能沿着石墨烯表面铺开生长，弄清大晶格失配下二硫化钼在石墨烯表面生长的动力学过程和机理。基于大面积高质量垂直异质结，构筑柔性太阳能电池；研究石墨烯及二硫化钼的层数、堆垛方式、应力等对异质结肖特基势垒的高度及电池性能影响规律，建立原子尺度上石墨烯与二硫化钼半导体接触模型。通过本项目的实施，为异质结的可控生长及在柔性光伏器件中的应用奠定基础。

柔性可穿戴是电子器件未来发展重要方向之一，而器件能源供给的持续性和柔性化是决定整个柔性器件效能的重要组成部分。石墨烯、二硫化钼等二维材料已表现出优异的光电性能和机械柔韧性，非常适合应用于柔性电子器件。本项目构筑了石墨烯/二硫化钼异质结器件并研究其光电特性及在太阳能电池中的应用。主要研究内容包括介电材料表面石墨烯/二硫化钼异质结可控制备，二硫化钼在石墨烯表面直接生长机制，组成异质结材料物性对结界面肖特基势垒的影响规律，以及柔性太阳电池构筑及性能研究四个方面。项目研究进展顺利，实现了二氧化硅和h-BN介电层表面层数可控、高质量石墨烯的快速生长。采用醇类（如甲醇和乙醇）作为碳源，在5-10min内实现二氧化硅衬底表面石墨烯的完全覆盖，生长速率高达~33.6 µm/s，相较于采用裂解温度更高的甲烷，其生长速率提高了3个数量级；所制备的石墨烯薄膜方阻0.9–1.2 kΩ/sq，室温空气中载流子迁移率115.4 cm2/V·s，两项指标可与部分采用镍和铜箔为催化剂生长的石墨烯相当。揭示了二硫化钼在石墨烯表面直接生长机制为范德华外延，直接生长的界面具有原子级的平整度，有利于光生载流子在石墨烯/二硫化钼界面分离，提高了光电流。建立了石墨烯与二硫化钼接触的能带结构图，并通过能带结构揭示了二者的物性对势垒影响规律。完成了石墨烯/二硫化钼异质结的整体转移，构筑异质结太阳能电池，并进行了相关测试。本项目研究结果为晶格大失配度异质结生长提供了理论指导，为介电材料表面石墨烯的直接生长提供了技术积累，也为二维材料应用于柔性太阳能电池提供了选择。