Investigation of nitrogen-doped carbon dot/ZnO nanocomposites and their application as interlayer in solution-processed organic light emitting diodes

Abstract

Nitrogen-doped carbon dots (N-CD) were synthesized and added to ZnO dispersions. The resulting composites were deposited between an emissive poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) layer and the top metal electrode of organic light-emitting diodes (OLEDs). The structural, morphological and optical properties of N-CD sample and composite films were investigated. In solid-state, the N-CD presented a highly anisotropic behaviour, with significant size change, as demonstrated in microscopic images. Nevertheless, it was found that small amounts of N-CD reduced the surface roughness of the ZnO films and facilitated electron injection from the electron transport layer (ETL) to the polymeric light-emitting layer, thus demonstrating that ZnO/N-CD composites with appropriate ratios can be successfully used as ETL to boost the performance of OLEDs. All the OLEDs investigated emitted the blue colour characteristic of PFO, with minor shifts in the chromaticity coordinates, suggesting that the N-CD did not play a significant role as light-emitters in these devices.