Oxide insertion layer in organic semiconductor devices

Open Access
Publisher Website
Google Scholar
Abstract
Organic semiconductors have been demonstrated for their potential in applications including organic photovoltaic (OPV),1−5 organic light-emitting diode (OLED),6−8 organic thin-film transistor,9, 10 as well as in efficient spin injection in organic materials.11, 12 OPV has attracted an enormous amount of attention due to growing energy requirements of the world and declining fossil resources.13 OPV cells offer considerable advantages over crystalline inorganic photovoltaic devices in terms of lower production cost and versatility of applications, such as lightweight, large-area, and flexible solar panels along with being more ecofriendly. A great deal of effort has been made in order to improve the charge transport and collection at the electrodes. Introduction of a high work-function (WF) transition metal oxide insertion layer between conducting indium tin oxide (ITO) and organic semiconductors was an attempt made by Tokito et al.14 More recently, it was reported that improved hole injection and stable device performance can be achieved by the insertion of a molybdenum oxide (MoOx) interlayer in OLED.15, 16 In OPV research, metal oxide as an interlayer between the ITO anode and the hole-collection layer was successfully demonstrated by Shrotriya et al.17 Irwin et al.18 has also demonstrated the efficiency enhancement by a thin nickel oxide insertion layer. Our recent results show 20% improvement in the fill factor and 35% reduction in the series resistance for MoOx interlayer between ITO anode and chloro-aluminum pthalocyanine (AlPc-Cl).19 The observations raised questions of how an insulating layer may reduce the resistivity, what the optimum thickness of such insertion layer is, and what the mechanism of this improvement is.