Injection modifications by ITO functionalization with a self-assembled monolayer in OLEDs

Spatially Modulating Interfacial Properties of Transparent Conductive Oxides: Patterning Work Function with Phosphonic Acid Self‐Assembled Monolayers

“…[13] A number of groups have incorporated SAMs into OLEDs, [1][2][3][4]6,[10][11][12]18,19] with many focusing on the use of phosphonic acid SAMs to modulate interfacial properties and improve device performance. [20][21][22][23][24][25][26] Given the strong influence SAM modifiers can have on the performance of organic electronic devices, the ability to microcontact print SAMs with large work function contrast is both scientifically interesting from the standpoint of creating model systems to explore the role of barriers and energy level offsets on charge injection in OLEDs, and technologically useful in the context of applications including low-cost illuminated signs and displays. [3,6] Although a limited amount of work has been performed in this area, notably by microcontact printing thiols on gold, [3,6] silanes on hydroxyl-terminated surfaces, [2,11,12] or phosphoryl chlorides on indium tin oxide (ITO), [27] these functional group/substrate combinations are not necessarily ideal for integration into OPV and OLED applications.…”

Modification of Transparent Conducting Oxide ( TCO ) Electrodes through Silanization and Chemisorption of Small Molecules

“…There is still some debate as to whether the enhancement in device performance is due to enhancements in wettability of the oxide surface toward the nonpolar molecules used in these devices, to changes in work function of the oxide surface, and/or to enhancements in intrinsic rates of charge injection [7][8][9][10][11][12][13]. Many of the same strategies initially used to enhance solution electron transfer rates on these oxide surfaces appear to positively impact device efficiencies in simple OLEDs and OPVs [9,[14][15][16][17][18]]. …”

Self‐assembled Electroactive Phosphonic Acids on ITO: Maximizing Hole‐Injection in Polymer Light‐Emitting Diodes

“…[8] The need for precise control of the electrode/organic semiconductor interface is particularly apparent in the field of polymer light-emitting diodes (PLEDs), where large differences between the work function of the commonly used indium tin oxide (ITO) anode and the highest occupied molecular orbital (HOMO) level of the organic semiconductor limit hole-injection and can lead to high turn-on voltage, low brightness, and low efficiency. Several approaches have been employed in decreasing the hole-injection energy barrier, such as oxygen plasma-treatment, [9,10] ultraviolet-ozone treatment, [11,12] inserting a dipolar layer, [13,14] tuning the surface energy of ITO with SAMs, [6,7,15] depositing a layer of conductive polymer (e.g., PEDOT:PSS), [16] and using an intermediate hole-transporting layer (HTL) having a HOMO level in between that of the ITO work function and the desired organic layer. [17,18] However, these treatments have some drawbacks.…”