Schottky-Barrier-Dependent Electrical Characteristics in Conjugated Polymer Transistors With Various Contact Metals

Despite the intensive study on the promotion of device performance, the device physics regarding the effects of Schottky barrier on the charge injection in conjugated polymer transistors still need more discussions. Here, the indacenodithiophene–co-benzothiadiazole (IDT-BT) organic field-effect transistors (OFETs) with four different contact metals (Pt, Au, Cu, and Cr) were fabricated to explore the effects. Different Schottky barriers were achieved with the contact electrode’s work function (W_F) varying. The I_ON/I_OFF ratio of IDT-BT OFETs increases from 10³ to 10⁶ as the W_F increases from 4.6 to 5.65 eV. The hole mobility also increases from 0.01 (for Cr) to 2.79 cm²V^–1s^–1 (for Pt) when the W_F approaches the highest occupied molecular orbital (HOMO) level of the conjugated polymer. Moreover, the threshold voltage and subthreshold swing of the devices both decrease with increasing the W_F. These could be ascribed to the lowered Schottky barrier with W_F, which promotes charge injection. The lowest Schottky barrier (0.123 eV) and contact resistance (1.06 × 10⁴ Ω⋅cm) can be achieved in the devices with Pt contacts, owing to the highest work function.