Comparison of top- and bottom-contact pentacene field-effect transistors using photocurrent microscopy

Overview Bottom-contact (BC) organic field-effect transistors (OFETs), though more industry-relevant than top-contact (TC) OFETs, are prone to low source-drain currents. The underlying mechanisms behind this remain debated. Thus, our work uses photocurrent microscopy (PCM) to examine charge injection in BC and TC geometries. PCM maps were generated first for OFETs with no electrode or gate dielectric treatments. Potential plots were quantitatively derived from the results using a method from previous work. [1] PCM maps were then collected for devices treated with 1. pentafluorobenzenethiol (PFBT), known to improve semiconductor morphology [2], and 2. UV-ozone, which is thought to enhance trap-assisted carrier transport. [3] These treatments were chosen, because they significantly increase source-drain current in BC devices, but in vastly different ways. In addition, unlike other photocurrent studies, we used a range of illumination wavelengths so as to probe various exciton states.