二维碳基材料制备改性及其在SIS结构光伏器件应用上的初探

发布时间：2018-06-08 18:28

本文选题：二维碳材料 + PECVD　；参考：《上海大学》2016年博士论文

【摘要】：石墨烯薄膜凭借其优异的电学和光学性质(透过率可达98%,载流子迁移率可达2×105 cm2/(V.S),电导率可达106 S/m),以及稳定的化学性能,使其在太阳能电池效率的提高和成本的降低上显示了很大的诱惑力。本论文从当前石墨烯薄膜的制备与改性,及其在光电-光伏应用中存在的问题(生长工艺复杂、沉积条件苛刻、薄膜质量差、薄膜导电性有待提高等)出发,以生长光电性能优异的二维碳基功能材料和改善SIS结构光伏器件的性能为目标,展开了以下几点研究。首先,利用射频等离子体化学气相沉积(RF-PECVD)技术制备了二维碳基薄膜材料,并系统地讨论了其生长过程中的热力学和动力学机理。同时进行了碳硅异质结器件的制备与光电性能的研究;然后,采用CVD技术制备了高质量的单层石墨烯薄膜,并将其转移到单晶硅上组装了不同结构的器件,研究了石墨烯薄膜对SIS结构器件光电性能的影响。最后,对石墨烯薄膜进行了氮元素掺杂改性,分析了其电子结构和电学性能以及其对器件性能的影响;主要研究内容和结果如下:(1)在不同沉积条件下,采用PECVD方法分别在不同衬底上沉积得到了不同结构和形貌的碳纳米材料。实验结果表明,采用PECVD方法,在无氢气无催化剂条件下沉积碳材料的过程中,当衬底温度保持在300~1000℃区间段时,对于碳材料的沉积都是可行的,且降低衬底温度会使得所生成的碳材料更易于出现缺陷;低温低压(500℃,100Pa)条件不利于石墨烯薄膜的生长;高温高压(900℃,100Pa)条件比较易于生成高质量的单层石墨烯薄膜;而在中等温度、中等压强条件下,更容易生成岛状、孤立不连续的碳材料。(2)系统的研究了影响PECVD方法生长碳薄膜材料的各种因素。结果表明:适宜的温度不但可以促进甲烷的分解,提供足够的能量形成成核位点,还能很好的控制碳薄膜材料的生长速率,有助于薄膜的低维生长;沉积时间增加虽然能使薄膜层数增加,有助于薄膜的连续性和均匀性生长,但时间过长薄膜的结构就会从量变到质变,从石墨烯转换为石墨材料;表面粗糙度适中的衬底既能帮助碳薄膜迅速形成成核中心,同时又能抑制它的过度成核和往垂直方向的堆叠生长,有利于低维碳薄膜—石墨烯的生长。(3)从热力学和动力学角度探讨了PECVD沉积碳薄膜的机理。结果表明,碳材料的化学气相沉积是复杂的气相化学反应和表面化学反应同时进行的过程。PECVD法生长碳材料的沉积条件和参数决定了其反应途径(实现性)和机理的不同,但总的热力学现实性是一定的。本研究中,甲烷的分解主要由热力学因素决定;随后碳氢自由基的气相反应则主要取决于反应动力学因素;最后,石墨烯的成核与生长则由衬底形貌、沉积温度等热力学和动力学因素共同决定。所以,可以通过调节诸如温度、压强和气体浓度等动力学因素来控制反应的路径与速率,进而可控的获得不同结构、形貌和功能需求的碳材料。(4)以甲烷为碳源使用CVD方法在铜箔衬底上制备出了大面积高质量的单层石墨烯薄膜,所制备的薄膜具有透过率高、迁移率高和导电性较好等特点。同时,为了结合晶硅太阳能电池器件结构和碳基太阳能电池的优势,将拥有特殊二维柔性结构和优异光电性能的石墨烯很好的耦合到SIS结构异质结器件中,解决了界面态与费米能级钉扎的问题,大大改善了短路电流与开路电压,进一步提高了电池的光电转换效率。结果表明,将石墨烯薄膜加入到ITO和晶硅中间作为缓冲层材料,不仅可以减少界面态,提高载流子的传输与收集;还可以改变其荷电状态,调节内部场,在SIS结构器件中起到很好的改性作用。(5)进行了石墨烯薄膜的掺杂改性方面的研究与探讨,采用原子替换的方式,实现了石墨烯的晶格掺杂,进一步改善了石墨烯薄膜的光电特性,提升了基于掺杂石墨烯薄膜的太阳能电池的光电性能。通过两步法成功的制备了以氮原子为异质原子的氮掺杂石墨烯薄膜,该薄膜表现出明显的n型半导体性能,载流子迁移率为521.8 cm2/V.s,成功的将石墨烯的电阻率降到了7.26×10-6Ω·cm。实验结果表明,在掺氮石墨烯薄膜中异质元素的进入对其导电性的影响是双重的。同时,掺氮石墨烯薄膜能很好地改善SIS结构太阳能电池的光电性能,使其转换效率达到6.24%。
[Abstract]:Graphene film, with its excellent electrical and optical properties (transmittance of up to 98%, carrier mobility up to 2 x 105 cm2/ (V.S), electrical conductivity up to 106 S/m), and stable chemical properties, makes it very tempting to improve the efficiency of solar cells and reduce cost. This paper has been prepared from the present preparation of graphene film. With the modification, the problems existing in the optoelectronic and photovoltaic applications (complex growth process, harsh deposition conditions, poor film quality, and film conductivity need to be improved, etc.), the following studies have been carried out for the growth of two dimensional carbon based functional materials with excellent photoelectric properties and the improvement of the properties of SIS structure photovoltaic devices. The two dimensional carbon based film materials were prepared by plasma chemical vapor deposition (RF-PECVD). The thermodynamic and kinetic mechanism in the growth process were systematically discussed. The preparation and photoelectric properties of the carbon and silicon heterojunction devices were also studied. Then, the high quality monolayer graphene film was prepared by CVD technology. The effects of graphene film on the photoelectric properties of SIS structural devices were studied by moving to the monocrystalline silicon. Finally, the nitrogen doping was used to modify the graphene film, and the electronic structure and electrical properties and its effect on the performance of the device were analyzed. The main contents and results are as follows: (1) different deposition strips. Carbon nanomaterials with different structures and morphologies were deposited on different substrates by PECVD method. The experimental results showed that the deposition of carbon materials was feasible and decreased when the substrate temperature remained at the interval of 300~1000 C in the process of depositing carbon materials without hydrogen without hydrogen catalyst without hydrogen. The substrate temperature can make the carbon materials more prone to defects; low temperature and low pressure (500 degrees, 100Pa) conditions are not conducive to the growth of graphene films; high temperature and high pressure (900 C, 100Pa) conditions are easier to produce high quality monolayer graphene thin film; and under medium temperature and medium pressure conditions, it is easier to produce Island, isolated discontinuous carbon. Materials. (2) a variety of factors that affect the growth of carbon films by PECVD method are systematically studied. The results show that the suitable temperature can not only promote the decomposition of methane, provide enough energy to form nucleating sites, but also can control the growth rate of carbon film material well, help the low dimensional growth of the film, and increase the deposition time, although it can make the deposition time increase The increase of the number of film layers contributes to the continuity and uniformity of the film, but the structure of the thin film will change from quantitative to qualitative and from graphene to graphite material, and the medium surface roughness can help the carbon film to form a nuclear center quickly, and also inhibit its excessive nucleation and vertical stacking growth. It is beneficial to the growth of low dimensional carbon film - graphene. (3) the mechanism of PECVD deposition of carbon films was discussed from the thermodynamic and kinetic point of view. The results show that the chemical vapor deposition of carbon materials is a complex gas-phase chemical reaction and a surface chemical reaction. The deposition conditions and parameters of the.PECVD long carbon materials determine their reaction. In this study, the decomposition of methane is mainly determined by thermodynamic factors in this study, and then the gas phase reaction of the free radical is mainly dependent on the kinetic factors; finally, the nucleation and growth of graphene is thermodynamically and dynamically based on the substrate morphology, deposition temperature and so on. Mechanical factors are decided together. So, we can control the path and rate of the reaction by adjusting the dynamic factors such as temperature, pressure and gas concentration, and then control the carbon materials with different structure, morphology and functional requirements. (4) a large area of high quality monolayer is prepared on copper foil substrate by CVD method with methane as carbon source. Graphene films have high transmittance, high mobility and good conductivity. At the same time, in order to combine the structure of silicon solar cells and the advantages of carbon based solar cells, the special two-dimensional flexible structures and excellent photoelectric properties are well coupled to the SIS structure heterojunction devices. The problem of interface state and Fermi energy level pinning has greatly improved the short circuit current and open circuit voltage, and further improved the photoelectric conversion efficiency of the battery. The results show that the addition of graphene film to ITO and crystalline silicon as a buffer layer can not only reduce the interface state, raise the transmission and collection of high carrier, but also change the charge of the charge. The state, adjusting the internal field, plays a very good modification role in the SIS structure. (5) the doping modification of the Shi Moxi film is studied and discussed. The lattice doping of graphene is realized by atomic substitution. The photoelectrical properties of the graphene film are further improved, and the solar energy based on the doped graphene film is enhanced. The photoelectric properties of the battery were successfully prepared by two step method. The nitrogen doped graphene film with nitrogen atoms as the heteroatom was prepared. The film showed obvious n type semiconductor properties and the carrier mobility was 521.8 cm2/V.s. The resistivity of the graphene was reduced to 7.26 * 10-6 Omega cm.. The results showed that the nitrogen doped graphene film was in the film. The influence of the entry of the heterogeneous elements on its conductivity is double. At the same time, the nitrogen doped graphene film can improve the photoelectric properties of the SIS structure solar cells and make the conversion efficiency to 6.24%.
【学位授予单位】：上海大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TB383.2;O613.71;TM914.4

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