Hot-wire vapor deposited tungsten and molybdenum oxide films used for carrier injection/transport in organic optoelectronic devices

Abstract

The purpose of this work is to give an account of the benefits gained by the use of hot-wire vapor deposited tungsten and molybdenum oxide thin films for carrier injection/transport in organic optoelectronic devices. The manuscript is divided in five parts: after a general introduction in organic (opto-) electronic devices, a brief theoretical introduction is done in the physics of transition metal oxides, with emphasis to tungsten and molybdenum, of organic semiconductors and of the semiconductor/metal contacts. Then the experimental method of hot-wire vapor deposition of tungsten and molybdenum oxide is described. Results, dealing mainly with the electronic structure and the microstructure of hot-wire tungsten and molybdenum oxide films are reported next. In particular, it is reported how the stoichiometry and the doping of these oxides with hydrogen alters their electronic structure. Then the benefits gained by using these hot-wire deposited oxide films for injecting/transport of carriers in organic light emitting diodes (OLEDs) and organic photovoltaics (OPVs) are reported and discussed in conjunction with the electronic structure of oxide films. Finally, it is concluded that the hot-wire vapor deposition of W and Mo oxide films is a simple, versatile and inexpensive technique allowing for the precise compositional control of the deposited layers, therefore their electronic structure. The use of such layers to modify the interfaces organic semiconductor/electrodes of OLEDs and OSCs causes significant improvements of the performance of these devices and improves spectacularly their stability in ambient air.