Systematic Investigation of Nanoscale Adsorbate Effects at Organic Light-Emitting Diode Interfaces. Interfacial Structure−Charge Injection−Luminance Relationships

Abstract

Molecule-scale structure effects at indium tin oxide (ITO) anode-hole transport layer (HTL) interfaces in organic light-emitting diode (OLED) heterostructures are systematically probed via a self-assembly approach. A series of ITO anode-linked silyltriarylamine precursors differing in aryl group and linker density are synthesized for this purpose and used to probe the relationship between nanoscale interfacial chemical structure and charge-injection/electroluminescence properties. These precursors form conformal and largely pinhole-free self-assembled monolayers (SAMs) on the ITO anode surface with angstromlevel thickness control. Deposition of a HTL on top of the SAMs places the probe molecules precisely at the anode-HTL interface. OLEDs containing ITO/SAM/HTL configurations have dramatically varied hole-injection magnitudes and OLED responses. These can be correlated with the probe molecular structures and electrochemically derived heterogeneous electron-transfer rates for such triarylamine fragments. The large observed interfacial molecular structure effects offer an approach to tuning OLED hole-injection flux over 1-2 orders of magnitude, resulting in up to 3-fold variations in OLED brightness at identical bias and up to a 2 V driving voltage reduction at identical brightness. Very bright and efficient (∼70 000 cd/m 2 , ∼2.5% forward external quantum efficiency, ∼11 lm/W power efficiency) Alq (tris-(8-hydroxyquinolinato)aluminum(III))-based OLEDs can thereby be fabricated.

Influence of Molecular Aggregation on Electron Transfer at the Perylene Diimide/Indium-Tin Oxide Interface

“…Transparent conductive oxides (TCOs) are essential electrode materials for applications in organic electronics, such as organic photovoltaics (OPVs), [1][2][3][4] organic thin-film transistors, 5 organic light-emitting diodes, 6,7 and perovskite solar cells. 8 Understanding and controlling the surface properties of TCO electrodes can improve the performance of these types of devices.…”

“…Furthermore, PDI redox potentials can be tuned, most effectively through substitutions at the "bay" (1,6,7,12) and/or "ortho" (2,5,8,11) positions, allowing them to be energetically matched to different active-layer and TCO materials. 25,26 In a recent study, 27 we began examining the properties of PDI monolayers tethered to ITO via phosphonic acid (PA) anchoring groups.…”

Modification of ITO surface using aromatic small molecules with carboxylic acid groups for OLED applications

“…ITO surface has been modified with SAM technique using suitable materials for hole injection to improve the interfacial compatibility [19] with charge transfer at the interface between ITO and organic hole-transport layer (HTL) [20]. To enhance such charge transfers in an OLED device, thereby improving turn-on voltage, brightness, and external quantum efficiency, coating of triarylamine-based molecules with trichlorosilane-binding groups on ITO as nanoscale layers were performed in the literature [21][22][23]. But, it is a very well-known fact that such kind of silane derivatives and trialkoxy silanes as well have a tendency to self-condensation in solution [24,25] causing the formation of uniform monolayers difficult.…”

Thiolate Chemistry: A Powerful and Versatile Synthetic Tool for Immobilization/Functionalization of Oligothiophenes on a Gold Surface

“…[23,[32][33][34] In particular, the double fixation of a p-conjugated system with a controlled horizontal orientation can be of both fundamental and technical interest. [34,35] Besides an improved stability related to multiple anchoring sites, [5f, 9a, 34] such horizontal orientation is considerably more efficient for absorption of incident light.…”