Synthesis and Application of 1,3,4,5,7,8-Hexafluorotetracyanonaphthoquinodimethane (F6-TNAP): A Conductivity Dopant for Organic Light-Emitting Devices

Conductivity dopants are used in organic light-emitting devices (OLEDs) to reduce the operating voltage and consequently improve the power efficiency. Here, we report the synthesis, as well as photophysical and electroluminescent properties, of an organic molecular p-type conductivity dopant: 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6-TNAP). F6-TNAP was obtained in a three-step two-pot synthesis from commercially available octafluoronaphthalene. When 1%-5% of F6-TNAP was coevaporated with N,N'-di-l-naphthyl-N,N'-diphenyl-1,1'-biphenyl-4,4'diamine (alpha-NPD) an absorption band at 950 nm was formed, which is attributed to charge transfer and assigned to the F6-TNAP radical anion. Single-carrier (hole-only) devices fabricated with F6-TNAP doped into alpha-NPD as the hole transport layer (HTL) show a >2 V decrease in operating voltage, compared to the undoped device. A decrease in operating voltage was also demonstrated in blue OLED devices using a F6-TNAP-doped HTL, with only a slight decrease in external quantum efficiency, thus resulting in a net improvement in power efficiency. These results demonstrate that F6-TNAP may be useful in generating high-efficiency OLEDs.