Phase separation induced high mobility and electrical stability in organic field-effect transistors

Abstract

Phase separation induced high carrier mobility and electrical stability are achieved in organic field-effect transistors using TIPS-pentacene:polystyrene blends. Rigid Si/SiO2 substrate was especially chosen to explore the phase separation. A vertical phase separation between TIPS-pentacene and polystyrene as confirmed from scanning electron microscopic image, evetually leads to excellent carrier mobility in polymer blend devices compared to that of neat TIPS-pentacene. Maximum hole mobility improved from 0.2cm2V−1s−1 for neat TIPS-pentacene on SiO2 to 2.6cm2V−1s−1 for TIPS-pentacene blends with PS, with average value of 1.5cm2V−1s−1. Apart from higher mobility, TIPS-pentacene:PS blend devices also showed much lower decay in drain current (∼30%) during a constant bias-stress of 2h, compared to neat devices (∼80%). Interestingly, This decay was fully recovered for blend devices under rest conditions. The corresponding shift in the threshold voltage due to bias-stress was lower for TIPS-pentacene:PS device due to better quality of interface as confirmed by lower values of density of interface traps and higher trapping time. High electrical stability in TIPS-pentacene:polystyrene blend devices was also supported by repeatabiliiy studies, which exhibited nearly unchanged device characteristics.