tuhin4u (Unstopable Lover + Mariana World DIAMOND member): A typical OLED is composed of a layer of organic materials situated between two electrodes, the anode and cathode, all deposited on a substrate. The organic molecules are electrically conductive as a result of delocalization of pi electrons caused by conjugation over part 0r all of the molecule. These materials have conductivity levels ranging from insulators to conductors, and are therefore considered organic semiconductors. *05-10-14 - 05:08:39
tuhin4u (Unstopable Lover + Mariana World DIAMOND member): The highest occupied and lowest unoccupied molecular orbitals ( HOMO and LUMO) of organic semiconductors are analogous to the valence and conduction bands of inorganic semiconductors. *05-10-14 - 05:09:27
tuhin4u (Unstopable Lover + Mariana World DIAMOND member): Originally, the most basic polymer OLEDs consisted of a single organic layer. One example was the first light- emitting device synthesised by J. H. Burroughes et al., which involved a single layer of poly (p-phenylene vinylene). However multilayer OLEDs can be fabricated with two 0r more layers in order to improve device efficiency. *05-10-14 - 05:10:55
tuhin4u (Unstopable Lover + Mariana World DIAMOND member): As well as conductive properties, different materials may be chosen to aid charge injection at electrodes by providing a more gradual electronic profile, 0r block a charge from reaching the opposite electrode and being wasted. Many modern OLEDs incorporate a simple bilayer structure, consisting of a conductive layer and an emissive layer. More recent developments in OLED architecture improves quantum efficiency (up to 19%) by using a graded heterojunction. *05-10-14 - 05:12:49
tuhin4u (Unstopable Lover + Mariana World DIAMOND member): In the graded heterojunction architecture, the composition of hole and electron-transport materials varies continuously within the emissive layer with a dopant emitter. The graded heterojunction architecture combines the benefits of both conventional architectures by improving charge injection while simultaneously balancing charge transport within the emissive region. *05-10-14 - 05:14:26