Mechanical and electrical stability of PEDOT: PTS and Au source/drain electrodes for bottom contact OTFTs on plastic films under bending conditions

Abstract

Two types of source/drain (S/D) electrodes, formed of poly(3,4-ethylenedioxythiophene): p-toluenesulfonate (PEDOT:PTS) conducting polymer and Au, were fabricated and mounted on flexible pentacene transistors. Several properties of the S/D electrodes were investigated: the adhesion between electrode and pentacene, the failure induced by mechanical bending, the electrical properties including contact resistance, and the field-effect mobility. The measurement of adhesive force using a 90 degrees peel tester revealed that the adhesive force of the pentacene-PEDOT:PTS interface was 200 N/m, while that of Au-pentacene was too small to be measured. The poor adhesion between the Au and pentacene led to the local delamination of the Au film, starting at a strain of approximately 1% and with a rapid increase of delamination density with increasing strain. The strain-induced mechanical damage has a direct effect on contact resistance, which in turn degrades mobility. In contrast, no delamination is observed with the high adhesive force at the pentacene-PEDOT: PTS interface, which thus led to a slight increase of contact resistance and mobility with strain. Consequently, the pentacene-PEDOT: PTS contacts provide mechanical and electrical stability in flexible organic thin film transistors (OTFTs) under bending tests.