Qinglan Huang

Progress in high work function TCO OLED anode alternatives and OLED nanopixelation

As organic light-emitting diodes (OLEDs) increase in sophistication and our understanding of building block-structure-luminous response mechanism increases, the remarkable properties of these heterostructures raise intriguing possibilities for future optoelectronics. In this contribution, we address two complimentary areas of interest in OLED science and engineering: (i) development and application of new transparent conducting oxide (TCO) materials for OLED anodes; (ii) effective OLED patterning strategies for nanofabrication.

Realization of high-efficiency/high-luminance small-molecule organic light-emitting diodes: synergistic effects of siloxane anode functionalization/hole-injection layers, and hole/exciton-blocking/electron-transport layers

High-efficiency/high-luminance small-molecule organic light-emitting diodes (OLEDs) are fabricated by combining thin, covalently-bound triarylamine hole injection/adhesion interlayers with hole- and exciton-blocking/electron transport interlayers in tris(8-hydroxyquinolato)aluminum (III) (Alq)-based OLEDs. Power and forward external quantum efficiencies as high as 15.2 lm/W and 4.4±0.5%, respectively, and turn-on voltages ∼4.5 V are achieved in devices of the structure ITO/TPDSi2/NPB/Alq:DIQA/BCP/Li/MgAg [NPB=(N,N′-di(1-napthl)-N,N′-diphenyl benzidine)] TPDSi2 interlayers are straightforwardly fabricated by spin-casting N,N′-diphenyl-N,N′- bis(p-trichlorosilylpropylphenyl)(1,1′-biphenyl)-4,4′-diamine TPDSi2 onto the ITO surface, while 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) interlayers are introduced by thermal evaporation. High quantum efficiencies are attributed to the synergistic enhanced hole/electron injection and exciton confinement effects of the TPDSi2 and BCP interlayers, respectively.

Small molecule organic light-emitting diodes can exhibit high performance without conventional hole transport layers

It is generally accepted that hole transport layers (HTLs) with thicknesses on the order of tens of nm are indispensable to the function of small molecule organic light-emitting diodes (OLEDs) if high electroluminescence and quantum efficiencies are to be achieved. In the present letter, small molecule OLEDs with high luminance and external quantum efficiencies are fabricated in which the HTL is replaced solely by an ultrathin (1–2 nm) self–assembled, saturated hydrocarbon organosiloxane monolayer. These results require some reconsideration of conventional design criteria regarding the necessity of HTLs and argue that the role of the self-assembled monolayer here is to enhance hole injection and charge recombination efficiency, while blocking electron transport to the anode. These results therefore offer significantly simplified device fabrication.

Triarylamine siloxane anode functionalization/hole injection layers in high efficiency/high luminance small-molecule green- and blue-emitting organic light-emitting diodes

High efficiency/high luminance small-molecule organic light-emitting diodes (OLEDs) are fabricated by combining thin, covalently bound triarylamine hole injection/adhesion interlayers with hole- and exciton-blocking/electron transport interlayers in tris(8-hydroxyquinolato)aluminum(III) (Alq) and tetrakis(2-methyl-8-hydroxyquinolinato)borate (BQ4−)-based OLEDs. Green-emitting OLEDs with maximum luminance ∼85000cd∕m2, power and forward external quantum efficiencies as high as 15.2lm∕W and 4.4±0.5%, respectively, and turn-on voltages ∼4.5V are achieved in devices of the structure, ITO∕N,N′-diphenyl-N,N′-bis(p-trichlorosilylpropylphenyl)(1,1′-biphenyl)-4,4′-diamine (TPD-Si2)/1,4-bis(1-naphthylphenylamino)biphenyl (NPB)/Alq doped with N,N′-di(3-heptyl)quinacridone (DIQA)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)∕Li∕AgMg. Also, bright and efficient blue-emitting OLEDs with turn-on voltages ∼5.0V, maximum luminance ∼30000cd∕m2, and ∼5.0lm∕W and 1.6±0.2% power and external forward quantum efficiencies,...

A polymer blend approach to fabricating the hole transport layer for polymer light-emitting diodes

This contribution describes an approach to fabricating high-efficiency hole-transport layers (HTLs) for polymer light-emitting diodes (PLEDs). HTLs fabricated by this approach have two components: a siloxane-derivatized, crosslinkable, hole-transporting material and a hole-transporting polymer. These HTLs exhibit high transparency, have no corrosive effects on the indium tin oxide anode, and have minimal pixel “cross-talk” potential. PLEDs that are fabricated using these HTLs exhibit superior performance (40% greater maximum current efficiency) versus analogous devices using a conventional poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) HTL. Most importantly, this approach has considerable flexibility and can be applied as a general strategy to manipulate energy level alignments in PLEDs.

Highly transparent and conductive CdO thin films as anodes for organic light-emitting diodes: Film microstructure and morphology effects on performance

— Highly conductive and transparent CdO thin films have been grown on glass and on single-crystal MgO(100) by MOCVD at 400°C and were used as transparent anodes for fabricating small-molecule organic-light emitting diodes (OLEDs). Device response and applications potential have been investigated and compared with those of control devices based on commercial ITO anodes. It is demonstrated that highly conductive CdO thin films of proper morphology can efficiently inject holes into such devices, rendering them promising anode materials for OLEDs. Importantly, this work also suggests the feasibility of employing other CdO-based TCOs as anodes for high-performance OLEDs.

Highly Transparent and Conductive CdO Thin Films as Anodes for Organic Light-Emitting Diodes

In this paper, CdO thin films are used for the first time as transparent anodes for organic light-emitting diodes (OLEDs). Highly conductive and transparent CdO thin films have been grown on glass and on single-crystal MgO(100) by low pressure metal-organic chemical vapor deposition (MOCVD) at 400°C, and were implemented in small-molecule OLED fabrication. Device response and applications potential have been investigated and compared with those of commercial ITO-based control devices. It is found that as-deposited CdO thin films are capable of injecting holes into such devices, rendering them promising anode materials for OLEDs. A maximum luminance of 32,000 cd/m 2 and an external forward quantum efficiency of 1.4 %, with a turn-on voltage of 3.2 V are achieved on MgO(100)/CdO-based devices.

Nanoprecise Self-Assembly of Electro-Optic and Electroluminescent Molecular Arrays

Although the current state of molecular synthesis has reached an impressive level of sophistication in the past decades, the ability of scientists to organize array of engineered molecular building blocks to achieve certain specific materials functions is currently in its infancy. Of particular attraction would be pathways which led via spontaneous self-organization processes to robust arrays of molecules with designed electronic and/or opto-electronic characteristics and spatial relationships. Ideally, the structural control of the assembly process would be at the sub-nm level and the structures would “click” into place after initial self-assembly. In the present contribution, we briefly discuss two complementary efforts to achieve such capabilities. In one effort, we focus on self-assembly routes to fabricate nanoscopically acentric arrays of high-hyperpolarizability building blocks for electro-optic function and in the other on the nanoscopic interfacial phenomena that tune charge injection and radiative recombination efficiencies in electroluminescent molecule-based organic heterostructures. Each approach makes use of well-characterized siloxane condensation chemistry, which can be used in successions of self-limiting chemisorptive processes, to deposit conformai, adherent, and virtually pin hole-free layers of molecular entities with sub-nm precision. An important consideration here is to apply a battery of physical characterization techniques to precisely define nanostructure and to correlate this with photonic response.