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

Abstract

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.