Lin Chiao-Chi, Lin Dong-Xuan, Lin Shih-He
Department of Materials Science and Engineering, Feng Chia University, Taichung 40724, Taiwan.
Nanotechnology. 2020 May 22;31(21):215705. doi: 10.1088/1361-6528/ab724f. Epub 2020 Feb 3.
Silver nanowire (AgNW) transparent electrode inevitably encounters ultraviolet (UV) irradiation from the environment, leading to stability and durability problems when in operation. Since UVA is the most abundant UV band and highly penetrating to AgNW related optoelectrical devices, it is crucial to understand the UVA damage caused to AgNWs. In this study, transparent electrodes composed of pristine AgNWs and glass substrates were manufactured with optimized processing parameters, and then used as model samples for aging tests. UVA exposure was conducted at elevated temperatures including 45 °C, 60 °C and 75 °C at 12 ± 5.5% relative humidity (RH) conditions. Comparative aging tests using conditions of damp heat (85 °C/85% RH) and 105 °C without UV (dark conditions) were also conducted. The relationship between optoelectrical property degradation, morphological changes and photo-corrosion was discussed. Under UVA exposure, the sheet resistance of electrodes increased gradually in an induction period before an abrupt change occurred. A nominal sheet resistance value of 200 Ω/sq was considered as a predestined failure of electrical property. It took 16, 24 and 60 h for UVA exposure at 75 °C, 60 °C and 45 °C, respectively, and 288 h by damp heat aging to degrade to the same status of predestined failure. Aging results of dark conditions indicated no degradation effect on AgNWs for 126 d aging. Moisture caused a different mechanism in damaging the capping agents on AgNWs. Nanocubes of silver chloride and sodium chloride were prone to precipitate at higher aging temperature such as 75 °C with UVA exposure. Sulfidation accounted for deterioration of optical transmittance, and occurred significantly at 45 °C with UVA irradiation and under damp heat conditions. The synergistic aging effect of UVA irradiance at elevated temperature on AgNW degradation has been unambiguously demonstrated. The results of this study provide guidelines for the design of optoelectronic devices when utilizing AgNW transparent electrodes.
银纳米线（AgNW）透明电极不可避免地会受到来自环境的紫外线（UV）照射，这导致其在运行时出现稳定性和耐久性问题。由于UVA是最丰富的紫外线波段，且对与AgNW相关的光电器件具有高度穿透性，因此了解UVA对AgNW造成的损伤至关重要。在本研究中，采用优化的工艺参数制造了由原始AgNW和玻璃基板组成的透明电极，然后将其用作老化测试的模型样品。在相对湿度（RH）为12±5.5%的条件下，于45℃、60℃和75℃等升高温度下进行UVA照射。还进行了湿热（85℃/85%RH）和105℃无紫外线（黑暗条件）的对比老化测试。讨论了光电性能退化、形态变化与光腐蚀之间的关系。在UVA照射下，电极的薄层电阻在突然变化之前的诱导期内逐渐增加。200Ω/sq的标称薄层电阻值被视为电气性能的预定失效。在75℃、60℃和45℃下进行UVA照射分别需要16、24和60小时，而湿热老化288小时会使其退化到相同的预定失效状态。黑暗条件下的老化结果表明，在126天的老化过程中，AgNW没有退化效应。水分对AgNW上的封端剂造成损伤的机制不同。在较高的老化温度如75℃且有UVA照射时，氯化银和氯化钠的纳米立方体容易沉淀。硫化导致光学透射率下降，在45℃有UVA照射和湿热条件下显著发生。已明确证明高温下UVA辐照对AgNW降解的协同老化效应。本研究结果为利用AgNW透明电极设计光电器件提供了指导。
