Influence of Surface Energy and Roughness on Hole Mobility in Solution-Processed Hybrid Organic Thin Film Transistors

Abstract

We investigate the influence of the surface energy and roughness on the hole mobility in organic thin-film transistors where a poly(3,3”'-dialkylquarterthiophene) (PQT-12) hybridized with an octyltrichlorosilane self-assembled monolayer is employed as the semiconducting layer on a silicon nitride (SiNx) gate insulator. Here, these surface properties are modified with varying the duration of oxygen plasma treatments on the SiNx surface, eluding to a different surface roughness and energy. From our analysis coupled with the experimental results, it is found that the surface roughness (Ra) controls the degree of surface roughness scattering (χSR) while the surface energy (ES) determines the reference mobility (μb), yielding the effective hole mobility expressed as a product of two terms associated with μb and χSR, respectively. It is found that μb follows a power law as a function of ES, and χSR grows exponentially with increasing Ra. In addition, a characteristics scattering length (λc) appears in the mobility expression, which turns out to be a demarcation, suggesting that Ra is required to be at least smaller than λc to minimize χSR.

Keywords

• Organic thin film transistors
• surface roughness scattering
• surface energy
• hole mobility