Ultrathin nanoclay films with tunable thickness as barrier layers in organic light emitting devices

Abstract

A novel concept where the inorganic ultrathin nanoclay (organo-treated montmorillonite) film is incorporated into the organic light-emitting diodes (OLEDs) as a buffer layer is exploited to enhance the performance and the stability of the devices. To precisely control the thickness of organoclay films within ∼1 nm scale, which can be a critical length in OLEDs research, we employ the charge-controlled deposition technique wherein the molecular interactions between nanoclay sheets and charged polymeric surface (mixture of poly(3,4-ethylenedioxythiophene) and poly(styrenesulfonate)) are elaborately manipulated. As a result, significantly improved device performance is observed for the case with the 5 nm thick clay films as compared to those without buffer layer, wherein the reduced turn-on voltage and the suppression of luminous efficiency (Cd A⁻¹) decay over time can be obtained. Eventually, device lifetime of the OLEDs is greatly enhanced and the brightness is maintained while minimizing the occurrence of dark spots. This substantial improvement in environmental stability of the device can be attributed to the role of the ultrathin nanoclay film which prevents the active polymer layer from directly contacting the indium contaminated and strongly acidic PEDOT:PSS bottom layer. In addition, it also works as a barrier film against the oxygen and moisture.