VATIS UPDATE Article

Developed by researchers at the Georgia Institute of Technology (Georgia Tech), the United States, and colleagues from three other institutions, the technique provides a new way of inducing p-type electrical doping in organic semiconductor films. The process involves briefly immersing the films in a solution at room temperature, and would replace a more complex technique that requires vacuum processing. “We believe this technique is likely to impact many other device platforms in areas such as organic printed electronics, sensors, photodetectors and light-emitting diodes,” said Bernard Kippelen, at Georgia Tech.

The research also involved scientists from the University of California, the United States, Kyushu University, Japan, and the Eindhoven University of Technology, The Netherlands. The technique consists of immersing thin films of organic semiconductors and their blends in polyoxometalate (PMA and PTA) solutions in nitromethane for a brief time – on the order of minutes. The diffusion of the dopant molecules into the films during immersion leads to efficient p-type electrical doping over a limited depth of 10 to 20 nanometers from the surface of the film.

The p-doped regions show increased electrical conductivity and high work function, reduced solubility in the processing solvent, and improved photo-oxidation stability in air. This new method provides a simpler alternative to air-sensitive molybdenum oxide layers used in the most efficient polymer solar cells that are generally processed using expensive vacuum equipment. For the first time, single-layer polymer solar cells were demonstrated by combining this new method with spontaneous vertical phase separation of amine-containing polymers that leads to efficient electron collection at the opposing electrode.