Fabrication of continuous polystyrene nanosphere/PEDOT:PSS conducting film and their use for organic light emitting diodes

Abstract

We herein propose an efficient, cost-effective method for producing a conducting thin film that combines efficient light extraction with enhanced stability in organic light emitting diodes (OLEDs). Continuous poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) film (PEDOT:PSS) with corrugated surface nanostructure was fabricated using an assembly of cross-linked polystyrene nanospheres (PS NSs) as template and was applied as a hole injection layer (HIL) in OLEDs. And, the 65-nm size PS NSs produce a random pattern of corrugated surface structures, which is ideal for enhancing light extraction without any spectral distortion and angle-dependence. For example, power and luminous efficiencies of the Ir(ppy)3-based solution-processable OLEDs with PS NS-PEDOT:PSS HIL were enhanced by factors of 2.0 and 1.4 respectively, compared to the control device. In addition, the improved device shows Lambertian emission pattern. It is also demonstrated that the PS NS-PEDOT:PSS HIL is highly effective in improving the ambient stability of solution-processable OLEDs. The continuous PEDOT:PSS domain in the HIL can be formed by utilizing significantly reduced amount of PEDOT:PSS (only 25 % compared to prisitine PEDOT:PSS film), which alleviates degradation induced by the acidic and hygroscopic nature of PEDOT:PSS. Stability enhancement by the factor of up to four is thus demonstrated in the proposed devices over the control device.