A strategy towards p-type doping of organic materials with HOMO levels beyond 6 eV using tungsten oxide

The authors present a concept to p-dope organic hole transport materials with highest occupied molecular orbital ( HOMO) levels on the order of 6 eV (e. g. 4,4',4 ''-tris(N-carbazolyl)-triphenylamine (TCTA) or 4,4'-bis(carbazol-9-yl)biphenyl (CBP)) by using WO3 as acceptor. Owing to its large work function, WO3 allows for efficient electron transfer from organic semiconductors with HOMO levels in this region. The effect of p-type doping is evidenced by optical absorption spectroscopy, electrical transport characteristics and Kelvin probe analysis. Moreover, OLED devices have been realized which exhibit 30% enhanced power efficiency due to the p-type doping. The results are expected to have a significant impact on the development of organic (opto-) electronic devices.