Electroluminescence from hybrid conjugated polymer -: CdS:Mn/ZnS core/shell nanocrystals devices

Reverse micelle-derived CdS:Mn/ZnS core/shell nanocrystals were synthesized with a core crystal diameter of 2.3 nm and a 0.4 nm thick ZnS shell and used as an electroluminescent material. Direct current (dc) electroluminescent (EL) devices were tested having a hybrid organic/inorganic multilayer structure of ITO// PEDOT-PSS//conjugated polymer//CdS:Mn/ZnS nanocrystal//Al, where two different conjugated polymers (poly(N-vinylcarbazole) (PVK) and poly(rho-phenylenevinylene) (PPV)) were used. The poly(3,4-ethylene-dioxythiophene)/poly(styrenesulfonate) (PEDOT-PSS) layer was used for enhanced hole injection from the ITO electrode. Orange and green EL emission was observed from devices with PVK and PPV devices, respectively. These data mean that electron-hole recombination is confined to the CdS:Mn/ZnS nanocrystalline layer in PVK-based devices but occurs in the PPV layer in PPV-based devices. Compared to a PPV EL device without a CdS:Mn/ZnS layer, the hybrid PPV-based nanocrystalline EL device showed large current flow and considerably enhanced EL emission. This suggests that the CdS:Mn/ZnS nanocrystal layer serves as an electron transport layer (ETL) in the hybrid device. These observations are shown to be consistent with the energy level diagrams of the EL devices.