Diffuser optimization for enhancing light extraction from light-emitting electrochemical cells

Light-emitting electrochemical cells (LECs) have enabled many novel solution-processable, low-cost, and flexible emission applications. Nevertheless, relatively inferior device efficiencies render LECs less competitive with other emission technologies. Light extraction would be a promising approach to enhance the device efficiencies of LECs. The diffuser film composed of a transparent photoresist layer doped with large and small TiO2 nano-particles (NPs) embedded between the indium-tin-oxide layer and the glass substrate has shown superior light extraction performance (>2.5X). However, the physical insight of optimization, e.g., adjusting the concentration of small TiO2 NPs in diffuser film, has not been explored yet. In this work, increasing the concentration of small TiO2 NPs is found to increase the thickness, roughness, and refractive index of the diffuser film. The optical simulation indicates that the thickness of the diffuser film has little effect on the light extraction. However, a higher roughness but a lower refractive index is preferred for the diffuser film to achieve better light extraction. As such, it is rational to expect that a proper concentration of small TiO2 NPs to reach a high enough roughness but still keep a relatively low refractive index is required for diffuser optimization. This study clarifies the physical mechanism responsible for diffuser optimization and thus shows a high potential for lighting applications of LECs.

Automated summary

Light-emitting electrochemical cells (LECs) have great potential for novel emission applications, but their relatively low device efficiency hinders their competitiveness with other emission technologies. A study finds that increasing the concentration of small TiO2 nano-particles in the diffuser film can enhance light extraction and improve the device efficiency of LECs.