17.4: Highly Power Efficient Organic Light-Emitting Diodes with a Novel P-Doping Layer

Abstract

We demonstrate p‐i‐n organic light‐emitting diodes (OLEDs) incorporating a p‐doped transport layer which comprises tungsten oxide (WO3) and 4,4′,4″‐tris(N‐(2‐naphthyl)‐N‐phenylamino) triphenylamine (2‐TNATA) to replace the volatile and low Tg F4‐TCNQ. We propose the 2‐TNATA:WO3 composition functions as a p‐doping layer which significantly improves hole‐injection and conductivity of the Alq3 based p‐i‐n OLEDs with long lifetime, low driving voltage (3.1 V), and high power efficiency (3.5 lm/W) at 100 cd/m2

p -type doping efficiency of MoO3 in organic hole transport materials

“…[4][5][6] Concomitantly, the need for thick organic layers to optimize the optical cavity of single and stacked OLEDs led to the application of p-type doping of hole transport materials by TMOs. [6][7][8][9][10] The reason for the wide range of applications of TMOs is associated with their high work function, indicating an electronic structure, which is suitable for p-type doping of even wide band gap materials with an energetically deep lying highest occupied molecular orbital ͑HOMO͒ level. Kelvin probe analysis has revealed a high work function of 6.7 eV for a neat film of WO 3 .…”

“…12 Interestingly, it appears to be a general observation, that the typically applied concentration of the TMO dopant in the organic matrix is rather high ͑up to 60 mol %͒. [6][7][8][9][10] This is in contrast to the established cases of p-type doping with tetrafluorotetracyanoquinodimethane ͑F 4 -TCNQ͒ where only a few mol % of dopant molecules are used. 13 Thus, the question about the doping efficiency in TMO doped hole transport materials is raised.…”