Solution-processable ambipolar organic field-effect transistors with bilayer transport channels

Ambipolar organic field-effect transistors (A-OFETs) allow a significant reduction in the complexity of organic integrated circuits (ICs) because they act as both n- and p-type transistors. In this paper, we report an efficient A-OFET based on the bilayer architecture of p-type poly(benzodithiophene(2-thienyl)-pyrrolopyrrole-dione) (PBDTTPPD) and n-type [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). By achieving the saturation condition of the dichloromethane (DCM) solvent for preparing the PCBM solution, we successfully obtained a complete bilayer of PCBM and PBDTTPPD and used it as a carrier transport layer in an A-OFET. The A-OFET exhibits clear bipolar transport and operates as an n-type and a p-type transistor in a single device. When a positive bias is applied between the gate electrode and the source electrode, the A-OFET serves as an n-type transistor with an n-channel generated for electron transport at the interface of PCBM and PBDTTPPD. On the other hand, it serves as a p-type transistor with a p-channel generated for hole transport at the interface between PBDTTPPD and SiO₂ when a negative bias is applied. The bipolar transport is modulated by morphology control using a 1,8-diiodooctane (DIO) additive and the PBDTTPPD layer thickness. The optimized A-OFET shows reasonable carrier mobilities for an ambipolar transistor with an average electron mobility of 2.22 × 10⁻³ cm² V⁻¹ s⁻¹ and an average hole mobility of 2.29 × 10⁻³ cm² V⁻¹ s⁻¹.