印刷银纳米线柔性透明电极及其可拉伸OLED器件关键问题研究

Silver nanowires (AgNWs) have recently attracted a lot of attention for potential applications as transparent electrodes in flexible wearable organic light-emitting devices (OLEDs) since their excellent photoelectrical properties and mechanical flexibility. However, several challenged issues must be addressed in the development of AgNW transparent electrodes and their stretchable OLEDs. (1) New low-cost, large area manufacture technologies need to be developed for the fabrication of patterned AgNW transparent electrodes. (2) The as-formed AgNW network electrode would exhibit poor conductive performance because of relative large nanowire cross junction resistance. (3) Stretchable OLED often shows low luminous efficiency due to lack of light out-coupling structure. This project addresses these important technology challenges through screen-printing large area patterned AgNW transparent electrode on glass substrate and microwave welding AgNWs to reduce the nanowire cross junction resistance. The AgNW transparent electrode would be transferred to the elastomeric polymer overcoat when it is peeled off the glass substrate. Furthermore, the metal oxide nanoparticles with high refractive index would be doped into the elastomeric polymer for increasing the refractive index of elastomeric polymer substrate and thus eliminating the total internal reflection at the organic/substrate interface. The quasiperiodic nanolens array would be fabricated on the surface of elastomeric polymer substrate by soft nanoimprinting technology to extract photons trapped within the substrate. Light out-coupling structures would be integrated into the electrode substrate to enhance light extraction efficiency of stretchable OLEDs. The mechanical failure mechanism of stretchable OLEDs would be explored through bending and stretching tests. The successful project implementation will offer important theoretical and practical foundations for development of large area patterned transparent electrodes and high performance stretchable organic optoelectronic devices.

银纳米线具有优异的光电特性和机械柔韧性，成为发展柔性可穿戴OLED器件最受瞩目的电极材料之一，但银纳米线透明电极及其可拉伸OLED器件发展面临的几个共性关键问题亟待解决：大面积制备图案化电极困难；银纳米线间接触电阻大；可拉伸OLED器件光输出效率低。本项目拟采用丝网印刷制备大面积图案化的银纳米线透明电极，利用微波焊接电极降低银纳米线间的接触电阻，通过剥离技术实现银纳米线嵌入弹性聚合物衬底表面的可拉伸透明电极。同时在聚合物衬底材料中掺杂高折射率的金属氧化合物纳米粒子，调控衬底折射率与有机层相匹配，消除波导模式光损失；在衬底表面压印准周期结构的微透镜阵列，抑制衬底模式光损失，将光耦合输出结构集成到电极衬底上，实现可拉伸OLED器件的光输出效率增强。通过器件的弯折和拉伸研究，初步探明可拉伸OLED器件的机械失效机理。项目的研究将为大面积透明电极及高性能可拉伸有机光电子器件的发展奠定重要的基础。

银纳米线具有优异的光电特性和机械柔韧性，成为发展柔性可穿戴有机电致发光器件（OLED）最受瞩目的电极材料之一。针对银纳米线透明电极大面积图案化制备困难、纳米线间接触电阻大，可拉伸OLED器件光输出效率低等问题，本项目围绕丝网印刷银纳米线透明电极及其微波焊接，弹性聚合物衬底光耦合输出结构集成，可拉伸OLED器件制备及其力学性能进行深入系统的研究。主要研究结果包括：（1）采用不含氟的表面活性剂调制出优异的银纳米线丝网印刷油墨，通过优化网板的目数，丝网印刷的角度和速度，结合油墨的优化，在柔性基底上印刷出不同图案的低方阻、高透过率和图案边界清晰的柔性透明电极；（2）采用钼酸铵、天然蜂胶等材料修饰银纳米线透明电极，研制的复合透明电极表面粗糙度为6.2 nm，方阻和透光率为15 Ω/sq和93%，并具有优异的机械弯折稳定性、热稳定性、抗湿和抗酸稳定性，其柔性白光OLED器件效率为56.6 cd/A；（3）通过在聚合物衬底中掺杂TiO2光散射纳米粒子和衬底表面压印非周期微纳透镜阵列，将光耦合输出结构集成到柔性透明电极衬底，抑制衬底和波导模式光损失，制备出效率为148 cd/A的柔性白光OLED器件，EQE达到46.1%；（4）系统研究了柔性透明电极和OLED器件的弯折稳定性，透明电极10000次弯折后方阻几乎无变化，器件在2000次弯折后亮度和效率的衰减小于10%，并初步探明了影响柔性可拉伸OLED器件机械稳定性的关键因素。本项目所研制的柔性透明电极可应用于OLED、触摸屏、电容器、传感器、电子皮肤、太阳能电池等领域，尤其是银纳米线/生物材料复合透明电极可进一步采用roll-to-roll技术大面积制备，有望获得产业化应用。我们提出的柔性透明电极与衬底光耦合输出结构集成策略已实现高效率的柔性OLED器件应用，该设计策略和实践经验可为高效柔性OLED器件的产业发展提供重要指引与参考。