A strategy to design substrate integrated flexible transparent electrodes for high-performance organic optoelectronic devices

Abstract

Flexible transparent electrode is an indispensable component in a great range of flexible optoelectronic applications such as solar cells, displays, transistors, sensors and touch screen. As for being high-performance and durable flexible electrodes in real applications, it is essential to develop new flexible transparent electrodes that need to fulfill the requirements of high transparency, good conductivity, smooth surface roughness, efficient charge transportation and appropriate work functions with adjoining functional layers, and robust reliability simultaneously under continuous electrical bias and repetitive mechanical bending at humid conditions. Among potentially valuable candidates for flexible transparent electrodes, silver nanowires are one of the promising candidates.

To promote the development and application of flexible transparent silver nanowire electrodes meeting the requirements above mentioned, we have conducted the following research work:

1. Achieve high-performance flexible transparent electrode via one-step multifunctional treatment for silver nanowire composites semi-embedded in low-temperature-processed substrate for highly performed flexible organic photovoltaics

A novel one-step multifunctional chemical approach is introduced into silver nanowire composites with conductive polymers to achieve a) selective welding at nanowires cross junctions to form Ag nanonetwork, b) removal of PVP from silver nanowires, and c) elimination of PSS from PEDOT:PSS. The low-temperature-processed substrate provides the protection of silver nanowires from the thermally activated Plateau–Rayleigh instability. By using the treated flexible electrodes, organic solar cells have been fabricated and achieved the high power conversion efficiency value of averaged 14.46% (best 15.12%).

2. Demonstrate practical stability of flexible transparent electrodes under multiple loads and its efficient charge extraction by chemical approach universally applicable to silver nanowire composites with metal oxide nanoparticles semi-embedded in colorless polyimide for durable and high-performance flexible organic photovoltaics

The proposed universal chemical approach on flexible transparent silver nanowire electrode composites with either n- or p-type metal oxide nanoparticles semi-embedded in colorless polyimide substrates provides a) removal of incoherent PVP ligands from Ag NWs, b) pinhole-free surface topography of the metal oxide nanoparticle films, and c) enhanced chemical integrations (bridged electrical/thermal pathways) between silver nanowires and metal oxide nanoparticles, simultaneously. The treated flexible transparent silver nanowire electrodes show excellent stability under continuous electrical bias and repetitive mechanical bending at humid conditions at the same time. The performance and stability of flexible organic solar cells based on the treated flexible transparent electrodes are highly improved with a record of high power conversion efficiency of 15.66 %. Notably, the outstanding stability of organic solar cells in electricity productions under both the AM 1.5G illumination and repetitive bending cycles has been achieved.

3. Investigate strategic design for improving external quantum efficiency of flexible inverted organic light-emitting diodes by silver nanowire composite electrodes semi-embedded in colorless polyimide

With designing the high refractive index contrast within flexible transparent silver nanowire electrode composites, its light-extraction efficiency in the fabricated organic light-emitting diodes is improved. In addition, the wide electron injection pathways in the flexible electrodes ensured to make the better charge balance factor. Consequently, the designed flexible electrode structures in organic light-emitting didoes show the increased external quantum efficiency.