化学气相淀积石墨烯在不同衬底上的表征以及多层石墨烯在有机太阳能电池中的应用

发布时间：2018-08-15 11:47

【摘要】：由于石墨烯具有不同寻常的物理性质，它的发现引发了物理学界的广泛关注。这种特殊的二维材料已被用于各种量子实验。不仅如此，石墨烯还具有独特的机械、光学、电学性质，使得石墨烯可以被用来制作各类新型器件。在室温下，石墨烯的电子迁移率高达200000cm2/V·s。如此高的载流子迁移率使得石墨烯有希望被用来制作高频高速晶体管。除此以外，石墨烯还有可能在其他方面得到应用，比如微机电系统MEMS、电池以及各类探测器。均匀大面积的石墨烯材料是确保石墨烯器件的高性能和推进该器件走向应用的关键。在目前的石墨烯制备方法中，化学气相沉积（CVD）法被认为是制备均匀大面积石墨烯的最佳制备方法之一。在CVD法制备石墨烯时，已经有多种不同的金属被用来作衬底，如铜、镍等。得益于铜箔表面的自限制作用，铜箔衬底上可以生长出大面积的单层石墨烯，因此铜箔已经成为CVD法制备石墨烯的最常用衬底。为了尽量增大石墨烯单晶的晶畴面积，本文提出电化学抛光的方法对铜箔进行预处理。实验结果表明，经过电化学抛光处理后的铜箔表面更加光亮干净，这有利于降低石墨烯的成核密度。为了制作石墨烯器件，生长结束后需要进行石墨烯转移。然而，在此转移过程中石墨烯容易受到有机物的污染。光刻胶杂质是测量石墨烯本征物理性质和制作石墨烯器件的障碍。为了去除石墨烯表面的有机物残留，通常在高温下对石墨烯进行退火。研究表明高温退火确实可以有效的去除光刻胶残留，可是高温退火对石墨烯本身的物理性质影响并没有深入的研究。本文把CVD制备的石墨烯转移到蓝宝石衬底上并且将其在不同的温度进行退火实验。利用AFM、拉曼光谱表征等手段，探究了高温退火工艺与衬底间残余应力的关系。通过分析Raman光谱，研究了石墨烯上残余应力的积累。并且在实验的基础上，本文进一步建立了退火残余应力的应力积累模型，获得是应力积累系数为0.35，由此模型导出的应力残余系数与实验结果取得了很好的吻合。铟锡氧化物ITO常用于制作有机太阳能电池的电极，然而其高昂的价格制约着太阳能电池的普及。不仅如此，铟锡氧化物十分易碎，，而且对酸十分敏感，使得可靠性下降。铟锡氧化物中本身化学性质较活泼，其中的离子容易渗入太阳能电池的有效层，造成有机太阳能电池性能下降，因此寻找到ITO的替代材料很有意义。石墨烯具有很高的透光率，单层石墨烯透光率高达97.7%，折射率小于0.1%，几乎可以忽略。虽然具有很高的透光率，但是未经掺杂的单层石墨烯方阻太高，不适合制作透明电极，而随着层数的增加，石墨烯的方阻会逐渐降低。所以为了制作透明电极，本文研究了叠层石墨烯转移工艺。这里提出了一种免于退火的叠层石墨烯转移方法，利用这种方法转移获得的叠层石墨烯同时具有较高的透光率和电导率。Raman测试表明，尽管随着叠层层数的增加，转移步骤增多，但是叠层转移工艺并没有破坏石墨烯以及引入非故意掺杂。实验获得是4层石墨烯电极的透光率超过86%，方阻小于100。本文在此基础上进一步制作了有机太阳能电池，得到的开路电压为0.62V，短路电流密度为0.51mA/cm2。证明这种转移工艺制备的叠层石墨烯电极，有潜力在有机太阳能电池中用来替代ITO。总之，本文主要在石墨烯生长、石墨烯与衬底间的相互作用、退火工艺在石墨烯中引入的残余应力、以及叠层石墨烯电极的制备和应用等方面进行了探索研究。
[Abstract]:Graphene has attracted much attention in the field of physics because of its unusual physical properties. This special two-dimensional material has been used in various quantum experiments. Moreover, graphene has unique mechanical, optical and electrical properties, making it possible to fabricate various new devices at room temperature. The electron mobility of the olefin is as high as 200,000 cm 2/V.s. Such high carrier mobility makes it possible for graphene to be used in high-frequency and high-speed transistors.
The uniform large area graphene material is the key to ensure the high performance of graphene devices and to promote the application of graphene devices.Chemical vapor deposition (CVD) is considered as one of the best methods to prepare uniform large area graphene in current graphene preparation methods. Due to the self-limiting effect of copper foil surface, a large area of monolayer graphene can be grown on copper foil substrate. Therefore, copper foil has become the most commonly used substrate for preparing graphene by CVD method. The results show that the surface of copper foil treated by electrochemical polishing is brighter and cleaner, which is beneficial to reducing the nucleation density of graphene.
In order to fabricate graphene devices, it is necessary to transfer graphene after growth. However, graphene is susceptible to organic contamination during this process. Impurities in photoresist are obstacles in measuring the intrinsic physical properties of graphene and in fabricating graphene devices. In this paper, graphene prepared by CVD was transferred to sapphire substrate and annealed at different temperatures. Characterized by AFM, Raman spectroscopy. The relationship between the high temperature annealing process and the residual stress between the substrates was investigated by means of the Raman spectroscopy. The accumulation of residual stress on graphene was studied by analyzing the Raman spectra. The coefficients agree well with the experimental results.
Indium tin oxide ITO is often used to make electrodes for organic solar cells. However, its high price restricts the popularity of solar cells. Moreover, indium tin oxide is very fragile and sensitive to acid, which makes it less reliable. Graphene has a very high transmittance. The transmittance of single-layer graphene is as high as 97.7%, and the refractive index is less than 0.1%. It is almost negligible. Although it has a very high transmittance, the undoped single-layer graphene has too high square resistance and is not suitable for use. As the number of layers increases, the square resistance of graphene decreases gradually.
In this paper, an annealing-free laminated graphene transfer method is proposed. The laminated graphene obtained by this method has high transmittance and conductivity at the same time. Raman test shows that although the transfer steps increase with the increase of the number of layers, the laminated graphene transfer process does not destroy the graphene and the introduction of unintentional doping. The experimental results show that the light transmittance of the four-layer graphene electrode is more than 86% and the square resistance is less than 100. Based on this, an organic solar cell is fabricated. The open-circuit voltage is 0.62V and the short-circuit current density is 0.51mA/cm2. Generation ITO.
In summary, the growth of graphene, the interaction between graphene and substrate, the residual stress induced by annealing process in graphene, and the preparation and application of laminated graphene electrode were studied in this paper.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN304.055;TM914.4

【共引文献】