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 (SiN x ) gate insulator. Here, these surface properties are modified with varying the duration of oxygen plasma treatments on the SiN x surface, eluding to a different surface roughness and energy. From our analysis coupled with the experimental results, it is found that the surface roughness ( $R _{a}$ ) controls the degree of surface roughness scattering ( $\chi _{\mathrm{ SR}}$ ) while the surface energy ( $E_{S}$ ) determines the reference mobility ( $\mu _{b}$ ), yielding the effective hole mobility expressed as a product of two terms associated with $\mu _{b}$ and $\chi _{\mathrm{ SR}}$ , respectively. It is found that $\mu _{b}$ follows a power law as a function of $E_{S}$ , and $\chi _{\mathrm{ SR}}$ grows exponentially with increasing $R_{a}$ . In addition, a characteristics scattering length ( $\lambda _{c}$ ) appears in the mobility expression, which turns out to be a demarcation, suggesting that $R_{a}$ is required to be at least smaller than $\lambda _{c}$ to minimize $\chi _{\mathrm{ SR}}$ .