Materials and interfaces issues in pentacene/PTCDI-C8 ambipolar organic field-effect transistors with solution-based gelatin dielectric

• Gelatin is a natural protein, which works well as the gate dielectric for pentacene/PTCDI-C8 ambipolar OFETs.
• The optimum condition occurs at pentacene/PTCDI-C8 with electron μFE of 0.85 cm2 V−1 s−1 and hole μFE of 0.95 cm2 V−1 s−1.
• Layer sequence, relative thickness and water absorption influence the device performance of ambipolar OFETs.

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-C8) 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 (μFE) values of pentacene/PTCDI-C8 ambipolar OFETs in vacuum and in air ambient. In contrast, water absorption in gelatin has higher contribution to the electron and hole μFE values in air ambient. The ambipolar performance of pentacene/PTCDI-C8 ambipolar OFETs depends on their layer sequence. For example, when PTCDI-C8 is deposited onto pentacene, i.e. in the structure of PTCDI-C8/pentacene, unbalanced ambipolar characteristics appear. In contrast, better ambipolar performance occurs in the structure of pentacene/PTCDI-C8. The optimum ambipolar characteristics with electron μFE of 0.85 cm2 V−1 s−1 and hole μFE of 0.95 cm2 V−1 s−1 occurs at the condition of pentacene (40 nm)/PTCDI-C8 (40 nm). Surprisingly, water absorption plays a crucial role in ambipolar performance. The device performance changes tremendously in pentacene/PTCDI-C8 ambipolar OFETs due to the removal of water out of gelatin in vacuum. The optimum ambipolar characteristics with electron μFE of 0.008 cm2 V−1 s−1 and hole μFE of 0.007 cm2 V−1 s−1 occurs at the condition of pentacene (65 nm)/PTCDI-C8 (40 nm). The roles of layer sequence, relative layer thickness, and water absorption are proposed to explain the ambipolar performance.

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