AVS 50th International Symposium
    Organic Films and Devices Tuesday Sessions
       Session OF+EM-TuA

Paper OF+EM-TuA3
Hybrid Electroluminescent Devices Based on Conjugated Polymers and CdS:Mn/ZnS Core/Shell Nanocrystals

Tuesday, November 4, 2003, 2:40 pm, Room 318/319

Session: Molecular and Organic Films and Devices-Optoelectronics
Presenter: H. Yang, University of Florida
Authors: H. Yang, University of Florida
P.H. Holloway, University of Florida
Correspondent: Click to Email
Nanocrystals with a CdS:Mn/ZnS core/shell structure with a core crystal diameter of 2.3 nm and a shell thickness of 0.4 nm were synthesized via a reverse micelle route. 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(p-phenylene vinylene) (PPV)) were used. The poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT-PSS) layer was used for enhanced hole injection from the ITO electrode. In PVK-based nanocrystal devices, only orange emission from the CdS:Mn/ZnS nanocrystal layer was observed, with no emission from the PVK. However, only green EL emission was observed from the PPV layer in PPV-based nanocrystal hybrid devices, with no emission from the nanocrystal layer. EL emission from a single layer of a multilayer structure was concluded to result from radiative electron-hole recombination occurring predominantly in that layer. All of these data will be interpreted in terms of energy levels for the PVK, PPV, and quantum-shifted CdS:Mn/ZnS structures, where a charge transport through the device depends upon the valence and conduction band offsets at the interfaces between conjugated polymer and nanocrystal layer. In addition, PPV-only EL devices showed much smaller current flow and weaker EL emission than PPV-based nanocrystal hybrid EL devices, suggesting that the CdS:Mn/ZnS nanocrystal layer serves as an electron transport layer (ETL) in the hybrid device. These observations will be shown to be consistent with the energy level diagrams of the EL devices.