Low Band Gap Furan-Flanked Diketopyrrolopyrrole-Naphthobisthiadiazole Based Conjugated Polymer/Stretchable Blend for Organic Field Effect Transistors

Abstract

N-type organic semiconducting materials that are compatible in stretchable organic field effect transistors (OFETs) still lag in performance behind that of p-type materials. Herein, a n-type conjugated polymer (DPPF-NTz) is reported that comprises a furan flanked diketopyrrolopyrrole (DPPF) as a monomer and napthobisthiadiazole (NTz) as a comonomer units, respectively, in a conjugated polymer backbone. The low band gap of 1.34 eV and suitable frontier energy levels allow its utilization in OFETs as an n-type semiconducting material. Optimized bottom-gate top contact OFETs based on chloroform and chloroform: o-dichlorobenzene processed DPPF-NTz showed a maximum electron mobility (µ_e) of 0.00042 cm² V⁻¹ s⁻¹ and 0.00078 cm² V⁻¹ s⁻¹, respectively, in devices annealed at 150 °C. Interestingly, upon mixing the DPPF-NTz with a stretchable polymer, polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS), yielded a stretchable semiconducting polymer composite, which displayed an enhanced µ_e of 0.0024 cm² V⁻¹ s⁻¹ in devices annealed at 250 °C over pristine DPPF-NTz. The improved µ_e and mechanical stretchability of the DPPF-NTz: SEBS polymer blend over pristine DPPF-NTz polymer is examined by nano-mechanical atomic force microscopy. The research investigation finding provides a critical insight into the structural and nano-mechanical properties of n-type stretchable polymer semiconductors, which are essential for the development of next-generation wearable OFETs.