ABSTRACT
Polypyrrole ...................................................................................... 305
3.3.1.4 SAM-TPD ....................................................................................... 307
3.3.1.5 Fluorocarbon Polymers ................................................................... 307
3.3.1.6 Inorganic Hole Injection Materials.................................................. 308
3.3.1.7 Doping the Hole Transport Materials ............................................. 308
3.3.2 Cathode Interfacial Materials ....................................................................... 309
3.3.2.1 LiF, CsF .......................................................................................... 310
3.3.2.2 M2O: Al (M: Li, Na, K, Rb) ........................................................... 310
3.3.2.3 Li=Cs Dopant with BCP and Li-Quinolate Complexes .................. 311 3.3.2.4 Organic Polymer Surfactants ........................................................... 311
3.4 Hole Transport Materials ........................................................................................ 312
3.4.1 Triarylamines ................................................................................................ 312
3.4.2 Triphenylmethanzes ...................................................................................... 320
3.4.3 Phenylazomethines and Their Metal Complexes........................................... 321
3.5 Electron Transport Materials................................................................................... 322
3.5.1 Metal Chelate Electron Transport Materials ................................................ 323
3.5.2 TPBI and N-Containing Aromatic Transport Materials .............................. 326
3.5.3 Oxadiazole and Triazole Transport Materials .............................................. 328
3.5.4 Fluorine-Substituted Electron Transport Materials ...................................... 328
3.5.5 Silole (Silacyclopentadiene) ........................................................................... 329
3.5.6 4n-p and Boron-Based Electron Transport Materials................................... 330
3.6 Light-Emitting Materials ......................................................................................... 330
3.6.1 Host-Guest Molecules .................................................................................. 332
3.6.2 Host Materials .............................................................................................. 333
3.6.2.1 Electron Transport Hosts ................................................................ 333
3.6.2.2 Hole Transport Hosts ...................................................................... 334
3.6.2.3 Silane Compound Host Materials for Blue and
White Phosphorescent Organic Light-Emitting Diodes................... 336
3.6.2.4 Fluorescent Blue Host Materials ..................................................... 337
3.6.2.5 Polymer Hosts ................................................................................. 338
3.6.3 Fluorescent Dopants ..................................................................................... 338
3.6.3.1 Green Fluorescent Dopants............................................................. 339
3.6.3.2 Red Fluorescent Dopants ................................................................ 343
3.6.3.3 Blue Fluorescent Emitters................................................................ 349
3.6.3.4 White Fluorescent Organic Light-Emitting Diodes ......................... 365
3.6.4 Phosphorescent Dopants............................................................................... 369
3.6.4.1 Synthesis of Iridium Complexes ...................................................... 370
3.6.4.2 Green Phosphorescent Dopants ...................................................... 372
3.6.4.3 Red Phosphorescent Dopants.......................................................... 375
3.6.4.4 Blue Phosphorescent Dopants ......................................................... 377
3.6.4.5 White Phosphorescent Organic Light-Emitting Diodes................... 379
3.7 Stabilizers and Hole-and Electron-Blocking Materials ........................................... 382
3.7.1 Stabilizers ...................................................................................................... 382
3.7.2 Sensitizers ...................................................................................................... 385
3.7.3 Hole-Blocking Materials ............................................................................... 386
3.7.4 Electron-Blocking Materials.......................................................................... 389
3.8 Current Best Performance of the Three Primary Color Materials and
Device Structures ..................................................................................................... 390
3.8.1 Red Emitters and Device Structures ............................................................. 391
3.8.2 Green Emitters and Device Structures .......................................................... 392
3.8.3 Blue Emitters and Device Structures............................................................. 393
3.9 Conclusion and Remarks ......................................................................................... 394
Acknowledgments ............................................................................................................ 395
References ........................................................................................................................ 395
Small-molecule organic light-emitting diodes (SMOLEDs), inspired by the search for blue
light-emitting devices based on organic crystals such as anthracene, can be traced back to the
early work of Pope et al. in the 1960s [1]. The development of thin-film organic electrolumin-
escent devices with relatively low driving voltages (below 30 V DC) by Vincett et al. at Xerox
Canada in 1982 was a major step forward in this field [2]. A significant breakthrough in
achieving high electrical efficiency OLEDs using small-molecule-based organic materials was
the discovery of the organic light-emitting diodes (OLEDs) reported by Kodak scientists in
1987 [3]. In that publication, a double layer consisting of thin films of a hole transport
triarylamine and a light emitting and electron transporting Alq3 layer, sandwiched between
a transparent indium tin oxide (ITO) electrode and an Al=Mg electrode, emitted green light under applied DC voltage. Although the quantum efficiency (QE) of such fluorescent
and
material based SMOLEDs is limited by spin statistics to only ~25%, the recently developed
phosphorescent SMOLEDs from the Princeton and USC groups achieved quantum efficien-
cies approaching 100% [4,5]. These efficiencies far exceed those of any previously described
devices. Such a fundamental breakthrough in device engineering and materials selection has
ignited progress in the OLED field (Scheme 3.1 shows the chemical structures of organic
materials used in the early studies). Undoubtedly, device construction, device engineering
and, particularly, new materials design continue to drive advances in this field.
