Reliable inkjet contact metallization on printed polymer semiconductors for fabricating staggered TFTs

Even though the fundamental benefits of the staggered bottom-gate top-contact geometry in organic thin-film transistors (TFTs) have been fully demonstrated for enhancing the charge injection efficiency, most printed organic TFTs with inkjet-printed source/drain electrodes have only been fabricated in bottom-contact configurations, probably due to the difficulty of printing with metal-nanoparticle ink on soluble organic semiconductor (OSC) without film deformation/dissolution. Here, we present the printing process and the electrical characteristics of inkjet-printed top contact OSC in bottom-gate TFTs. We first fabricated polymer bottom-gate TFTs by printing in two different top- and bottom-contact configurations. The physical carrier mobility of the two TFTs was extracted from a gated-contact organic TFT model to exclude the effect of geometric contact resistance R_C. When compared to assess the OSC film damage from the printing metallization, the two mobility values were almost identical. This result indicates that the metal nanoparticle ink used in this work formed a top metal contact on the OSC film without significant chemical damage. Furthermore, the printed top-contact TFT exhibited I–V characteristics almost identical to those of a thermally evaporated Ag top-contact TFT. This study suggests the possibility of inkjet-printed top metal contacts for organic thin-film devices such as transistors, solar cells, and diodes.