Abstract
Gelatin is a natural protein, which works well as the gate dielectric for pentacene/N,N-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C 8 ) ambipolar organic field-effect transistors (OFETs) in air ambient and in vacuum. An aqueous solution process was used to form the gelatin gate dielectric film on poly(ethylene terephthalate) (PET) by spin-coating and subsequent casting. Pentacene morphology and interface roughness are two major factors affecting the electron and hole field-effect mobility (μ FE ) values of pentacene/PTCDI-C 8 ambipolar OFETs in vacuum and in air ambient. In contrast, water absorption in gelatin has higher contribution to the electron and hole μ FE values in air ambient. The ambipolar performance of pentacene/PTCDI-C 8 ambipolar OFETs depends on their layer sequence. For example, when PTCDI-C 8 is deposited onto pentacene, i.e. in the structure of PTCDI-C 8 / pentacene, unbalanced ambipolar characteristics appear. In contrast, better ambipolar performance occurs in the structure of pentacene/PTCDI-C 8 . The optimum ambipolar characteristics with electron μ FE of 0.85 cm 2 V -1 s -1 and hole μ FE of 0.95 cm 2 V -1 s -1 occurs at the condition of pentacene (40 nm)/PTCDI-C 8 (40 nm). Surprisingly, water absorption plays a crucial role in ambipolar performance. The device performance changes tremendously in pentacene/PTCDI-C 8 ambipolar OFETs due to the removal of water out of gelatin in vacuum. The optimum ambipolar characteristics with electron μ FE of 0.008 cm 2 V -1 s -1 and hole μ FE of 0.007 cm 2 V -1 s -1 occurs at the condition of pentacene (65 nm)/PTCDI-C 8 (40 nm). The roles of layer sequence, relative layer thickness, and water absorption are proposed to explain the ambipolar performance. © 2014 Elsevier Ltd. All rights reserved.