Carrier transport mechanisms of hybrid ZnO nanorod-polymer LEDs

Abstract

A hybrid polymer-nanocrystals (NC) light-emitting diode (LED) device with the hole-conducting polymer poly (9-vinyl carbazole) (PVK) and ZnO nanorods (NRs) composite structure of glass/indium-tin-oxide (ITO)/(PEDOT:PSS/PVK + ZnO nanorods)/Al is simply fabricated by a spin coating. In currentvoltage characteristic curve measurement, negative differential resistance (NDR) phenomenon is observed where Al electrode is directly deposited on PVK instead of ZnO NRs. Such an inhomogenous deposition is caused by the agglomeration of ZnO NRs and their low probability of adsorption on PVK due to twodimensional structural property. Carrier transport behavior in the LED device is well described by both ohmic and spacecharge- limited-current (SCLC) processes. Broad blue electroluminescence (EL) consisting of two sub peaks centered at 441 nm and 495 nm is observed, which indicates that the ZnO nanorod plays as a recombination center of exciton. Red shift in EL position compared to photoluminescence can be well explained by band offsets happened at the heterojunction between PVK and ZnO NRs.