Synthesis and Characterization of Zinc based Electroluminescent Metal Complexes for their Applications in OLEDs

Abstract

Organic semiconductors have attracted lot of attention in technological community due to its potential applications in organic light emitting diodes (OLEDs), organic photovoltaic cells and field effect transistor etc. OLED is being considered as one of the most promising technology for flat-panel displays and in general lighting. An organic light emitting diode (OLED), is a light emitting diode whose emissive electroluminescent layer is composed of a film of organic compounds. The layer usually contains a polymer substance or small molecular weight metal chelates that allow suitable organic compounds to be deposited. The small molecule based metal chelates are the appropriate candidates as they are processed by conventional vacuum deposition techniques. Small molecule based Zn metal complexes can be used in OLED devices as electron and hole transport layer. It can also be used as an emissive layer because of their wide spectral response in the visible region. Two Zinc based Photoluminescence metal complexes Zinc(2,2’-bipyridine)-5-chloro-8- hydroxyquinoline and Zinc(2,2’-bipyridine)-5-7-dichloro-8-hydroxyquinoline have been synthesized and characterized by different characterization techniques (FT-IR, TGA, UV visible and Photoluminescence Spectroscopy). Both the Photoluminescence and electroluminescence properties are extensively studied. The Photoluminescence properties of Zinc(2,2’-bipyridine)-5-chloro-8-hydroxyquinoline shows maximum absorption at 360 nm, photoluminescence peak at 534 nm and that of Zinc(2,2’-bipyridine)-5-7-dichloro-8- hydroxyquinoline shows maximum absorption at 360 nm, photoluminescence peak at 560 nm. The x-ray diffraction analysis of the materials Zinc(2,2’-bipyridine)-5-chloro-8- hydroxyquinoline and Zinc(2,2’-bipyridine)-5,7-dichloro-8-hydroxyquinoline have been studied, which shown below in figure 4.5. The result shows the first material is amorphous in nature and second one shows some crystalline nature at an angle 2θ=23.455. The crystallite size at 2θ=23.455, is 168.605nm. Device have been fabricated with the structure ITO(120nm)/α-NPD(50 nm)/Zinc (2,2’-BPY)- 5,7-dichloro-8-hydroxyquinoline(50nm)/LiF(1nm)/Al(150 nm) by using the synthesized zinc complexes, Zinc (2,2’-BPY)-5,7-dichloro-8-hydroxyquinoline as emissive material. Device shows wide electroluminescent spectra which peaks at 560nm and turn-on voltage is 10V.