Organic light-emitting diodes using 3,6-difluoro-2,5,7,7,8,8-hexacyanoquinodimethane as p-type dopant

We demonstrate that 3,6-difluoro-2,5,7,7,8,8-hexacyanoquinodimethane (F2-HCNQ) can serve as an excellent electrical doping material for hole transport materials with the highest occupied molecular orbital level as high as 5.4 eV, such as N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB). With its relatively strong electron-accepting ability and high thermal stability, F2-HCNQ doped NPB organic light-emitting diode (OLED) showed improved power efficiency with low driving voltage. The tris(8-hydroxyquinoline)aluminum based OLED with F2-HCNQ doped NPB layer and Cs2O doped bathophenanthroline electron transport layer exhibits power efficiency of 3.6 lm/W with driving voltage of 3.2 V at 100 cd/m2.