An improvement of performance in n-channel organic field effect transistors with N-phenyl[60]fulleropyrrolidines by molecular doping

Abstract

The high performance of soluble [60]fulleropyrrolidine upon its use as the active layer of n-channel organic field-effect transistors (OFETs) is reported. The two materials, N-phenyl derivatives C60-fused-N-phenyl-2-phenylpyrrolidine ([C60]PhNPh) and C60-fused N-phenyl-2-hexylpyrrolidine ([C60]HexNPh), have well-controlled molecular structures with a modification of the pyrrolidine ring, with no increase in the LUMO level, achieving a high mobility and highly ambient stable n-type OFET. The top-gate, bottom-contact device shows a high electron charge-carrier mobility of up to 0.14 and 0.08 cm² V⁻¹ s⁻¹ for [C60]PhNPh and [C60]HexNPh, respectively, (I_on/I_off = 10⁶) with the commonly used CYTOP dielectric. Excess carriers introduced by a small amount of chemical doping of polyethyleneimine (PEI) compensate traps by shifting the Fermi level (E_F) toward the respective transport energy levels and therefore increase charge-carrier mobility (0.26 and 0.1 cm² V⁻¹ s⁻¹) and provide good ambient operational stability compared with pristine devices.