Electric Field Promotes Pentacene Dimerization in Thin Film Transistors

Density functional theory (DFT) calculations were used to assess the effect of electric fields of varying magnitudes and directions on the molecular structure of pentacene and other acenes. The aim is to understand the response of acenes in organic field effect transistors, specifically the structure of the first monolayer(s) deposited on the gate dielectric, where the transversal electric field and the charge carrier density are largest and charge transport occurs. Pentacene cycloaddition can be enhanced by the application of electric fields oriented along the direction of the forming bonds. Dimerization is likely to occur in low-density, disordered domains, such as grain boundaries or terrace edges. Together with other factors, dimerization could affect device performance leading to an irreversible decrease of mobility due to the creation of new trap states.