可见和近红外光照下石墨烯透明电极导电性能变化机理研究

Graphene becomes an ideal alternative to traditional transparent electrode for its excellent features. Nowadays, the large area graphene thin film has gone into mass production. Devices based on the graphene electrode will be put into practical application in the near future. However, the conductivity of graphene will degrade slowly under visible irradiation, which is a major weakness for its long-term application as transparent electrode. For this problem, the mechanism of conductivity change for graphene transparent electrode under visible and near-infrared irradiation will be analyzed in this research. Methods for improving long-term stability of graphene thin film will be put forward as well. According to the actual application conditions of the transparent electrodes, this research will focus on the irradation effects in the visible range. The opposite phenomenon in near-infrared irradiation will be discussed in comparison. Based on the photothermal and photoabsorption/photodesorption effects, which are the main mechanisms, the influences of sample parameters, environment conditions and irradiation parameters on the conductivity change will be fully analyzed. Then, the main mechanism and influencing factors leading to the conductivity change will be revealed. Furthermore, the sample parameters with the minimum influence by visible irradiation and the corrosponding making processes can be summarized as a basis to improve the long-term stability of conductivity for graphene thin film. This research can provide theoretic supports and practical reference to ensure the reliability of optoelectronic devices with graphene transparent electrode.

石墨烯因其优良特性成为传统透明电极的理想替代品，目前大面积石墨烯薄膜已进入量产阶段，基于石墨烯透明电极的器件也将从实验室走向大众应用。然而，光照会导致石墨烯薄膜导电性能发生缓慢退化，不利于其作为透明电极长期应用。针对此问题，本项目将开展石墨烯透明电极光致电导变化机理分析和长期工作稳定性改善研究。根据透明电极实际应用条件，项目将对石墨烯薄膜在可见光辐照下电导变化现象进行重点研究，通过与近红外光辐照下完全相反的电导变化现象进行对比分析，从光热效应和光致吸附/解吸附作用这两种最可能的物理效应出发，全面分析样品参数、环境气氛和辐照条件对光照下石墨烯透明电极导电性能的影响，揭示光致电导变化产生的主要物理机理和影响因素。进一步，通过机理研究得到受光照影响最小的样品参数及相应处理方法，作为改善石墨烯透明电极稳定性的依据并进行长期光照实验验证，为促进基于石墨烯电极的光电器件长期稳定应用提供理论和技术支持。

石墨烯具有良好的导电性、透光性、柔韧性等显著优势，是理想的透明薄膜电极材料。透明电极主要在可见光和近红外波段范围工作，石墨烯薄膜作为透明电极应用时，将长期在光辐照状态下工作，而一些实验现象表明石墨烯在光辐照下会产生明显电学性能变化，对其能否在长期应用时保持性能稳定蒙上阴影。为此，本项目开展了石墨烯在可见和近红外光辐照下的电学参数稳定性进行系统深入研究。.项目全面研究了样品参数、环境气氛和辐照条件对光辐照下石墨烯透明电极导电性能的影响，并从光热效应和光致吸附/解吸附作用出发，分析了光致电导变化产生的主要机理和影响因素及程度。具体实验内容包括：将CVD法制得的铜基石墨烯转移至PET、SiO2和玻璃基底上，并对部分样品掺杂AuCl3处理，再图形化获得样品。设计了石墨烯辐照实验系统，实现在真空、大气和氮气环境氛围中，光功率密度可调的红绿蓝三种可见光和近红外光对不同参数的石墨烯样品进行辐照，并高精度实时测量石墨烯光辐照下电阻的变化。.实验结果表明：①石墨烯在光照时电阻增大，停止光照电阻降低；②蓝光对石墨烯导电性能变化影响最大，绿光次之，红光最小；③ SiO2基石墨烯导电性能受可见光辐照影响最大，玻璃基次之，PET基影响最小；④ 掺杂后PET和玻璃基石墨烯光照电学稳定性下降，SiO2基稳定性增提高；⑤ 真空环境中石墨烯光照电学稳定性更强；⑥近红外光辐照对石墨烯导电性能影响有限。.通过将暗态环境下石墨烯薄膜电阻变化同温度的关系与基底温升范围进行对比，排除了光热效应的影响，得出光致吸附是引起石墨烯导电性能变化的主要原因。进一步分析可知，光辐照引起石墨烯表面力场改变，使得材料表面吸附或脱附表面附近的环境分子、微粒以及基底分子，使载流子浓度发生变化，进而改变石墨烯的电导率。辐照光源波长和功率、掺杂、环境氛围、基底材料、辐照时长都会对光致吸附／脱附作用产生不同程度的影响，使载流子浓度发生不同的程度的改变，从而使石墨烯的电导率发生不同程度的变化。