Aug 29, 2008
The fabrication of new functional optoelectronic devices
Until now, we have studied flexible non-volatile organic bistable devices by using a hybrid polymer-CdSe/ZnS quantum-dot (QD) system. In a recent article published in Nanotechnology by D I Son et al., more has been researched about the organic bistable device (OBD) structure and its physical mechanism.
We thoroughly compared the differences between LED and OBD structures, by dispersing CdSe/ZnS QDs with organic materials. Through very careful transmission electron microscopy (TEM) studies, we showed that CdSe/ZnS QDs are located at the surface of PVK polymer particles in the OBD device, and they are distributed over the interface of PVK and TPBi, as well as the surface of TPBi, in the LED device in this single active-layer scheme. This was as expected. It was also revealed that the OBD functionality can be converted into the LED, just by inserting an electron transporting layer (ETL) and controlling the band-gap dependence on the lowest unoccupied molecular orbital (LUMO) level of the ETL side.
Because this hybrid polymer–QD dual-function device can be demonstrated as a combined form of electrical bistability for the non-volatile memory function and QD LED for the electroluminescent displays, we could also expect that the fabrication of hybrid OBD and LED devices will present a united one-board type of display and memory device in the near future.
Through our lab-fabrication process, each functional device is fabricated with a single active-layer structure, on both sides of a common glass substrate under ambient conditions. In a single active layer where inorganic semiconductor QDs are uniformly embedded in polymer nanoparticles, the electrical bistability and the electroluminescence mechanism are carefully investigated with the detailed physical explanation about the energy-level realignment of constituent nanocomposite materials.
Our interesting results about the CdSe/ZnS QD-based dual-function devices with simple and easy fabrication approaches by using a conventional spin-coating method, show the strong possibilities of future transparent optoelectronic devices based on hybrid polymer–QD systems.
About the author
Dong-Ick Son is a PhD student researcher at Korea Institute of Science and Technology (KIST) and a PhD student at the department of Information Display Engineering, Division of Electronics and Computer Engineering in Hanyang University. Dong-Hee Park is a research scientist in the Materials Science and Technology Research Division at KIST. Sang-Yub Ie is a postdoctoral researcher who moved from Yonsei University to KIST in Korea last year. Ji-Won Choi is a senior research scientist in the Thin Film Materials Research Center at KIST. Fushan Li is a postdoctoral researcher who moved from Beijing University in China to Hanyang University in Korea in 2006. Tae-Whan Kim is a professor of the Division of Electronics and Computer Engineering at Hanyang University. Won-Kook Choi, who is a team leader, is a principal research scientist in the Materials Science and Technology Research Division at KIST.