Continuous Modulation of Electrode Work Function with Mixed Self-Assembled Monolayers and Its Effect in Charge Injection

Abstract

Self-assembled monolayers (SAMs) of binary mixtures of n-decanethiol and the fluorinated analogue (3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluoro-1-decanethiol) were formed on silver surface. The film structure was characterized by reflection absorption IR and XPS to be a homogeneous mixture of the two components. The mixed monolayers serve to tune the work function of silver over a wide range by varying the surface composition of the mixed monolayer from 4.1 to 5.8 eV. The mixed SAM-modified Ag surfaces were used as the anode in the fabrication of hole-only devices with the device structure Ag/SAM/HTL/Ag, where HTL represents a hole-transporting layer. It is shown that depending on the HTL used and thus the HOMO level involved, the maximum current injection into the device occurred with differently modified Ag. Top-emitting organic light-emitting diodes fabricated with differently modified silver electrodes showed that the maximum current and maximum luminance efficiency occur at anodes of different modifications due to a change in the hole-electron charge balance.

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

“…Self-assembled monolayers (SAMs) have been used to modify the surface chemistry of polymer, [1,2] metal, [3][4][5][6][7][8][9] and metal oxide [10][11][12][13][14][15][16] electrodes in order to control properties including wettability, work function, and charge transfer, by using many functional group/substrate combinations. Examples range from thiols on gold, [3][4][5][6][7][8] to silanes on hydroxyl-terminated surfaces, [11,12,15,17] to mixtures of SAMs containing different terminal functional groups on metal oxide buffer layers. [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.…”

“…Examples range from thiols on gold, [3][4][5][6][7][8] to silanes on hydroxyl-terminated surfaces, [11,12,15,17] to mixtures of SAMs containing different terminal functional groups on metal oxide buffer layers. [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.…”

Binary functionalization of H:Si(111) surfaces by alkyl monolayers with different linker atoms enhances monolayer stability and packing

“…26 A similar study on gold, using deposited alkanethiol SAMs with two different terminal groups, namely carboxylic acid and amine, reported a linear relationship between the concentration of each SAM and the surface WF; the WF varies within the boundaries set by functionalization with the corresponding single components. 27 Mixed functionalization can afford electronic tunability on semiconductor substrates.…”

Pulsed-Laser Ablation of Au Foil in Primary Alcohols Influenced by Direct Current

“…As an excellent example, the modification by amino-and/or mercapto-alkylsiloxane, or porphyrins can be referenced (Buining et al, 1997;Doron et al, 1995;Grabar et al, 1996;Šloufová-Srnová & Vlčková, 2002;Sládková et al, 2006). Obviously, surface modifications may be useful in or, on the contrary, disable some applications because they change electrical and optical properties of nanoparticles as well as of substrates (Carrara et al, 2004;de Boer et al, 2005;Durston et al, 1998;Rotello, 2004;Schnippering et al, 2007;Wu et al, 2009). Therefore, many research groups look for other types of nanoparticles assembling.…”