SOLUTION-PROCESSED DOPED POLYMER ORGANIC SEMICONDUCTORS

Abstract

Achieving an ohmic contact is essential for high-performance semiconductor devices. A good ohmic contact between the electrode and the semiconductor layer is one that can inject the maximum current density across the contact. This requires ultra high and ultra low workfunctions electrodes to inject holes and electrons respectively. However, it is challenging to produce electrically conducting films with sufficiently high or low work functions, especially for solution-processed semiconductor devices. The key challenges are stabilizing the thin films against de-doping and suppressing dopant migration. In this thesis, the use of solution-processed self-compensated ultra high and ultra low workfunction doped polyelectrolytes was demonstrated to achieve ohmic contacts to organic devices. The hygroscopicity of the conjugated polyelectrolyte films were investigated and water was found to be the cause of dedoping for ultra high workfunction doped polymers, thus limiting the workfunctions of hole-doped polymers. This, however, can be suppressed by using a less hygroscopic counter-ion.