Critical Impact of Source/Drain Surface Modification Treatment on the Performance of 4H-21DNTT OTFT

The metal/semiconductor interface plays a crucial role in determining contact resistance and it significantly influences the performance of organic thin-film transistors (OTFTs). The quantitative impact of UV–ozone (UV–O3) and 2,3,4,5,6-pentafluorothiophenol (PFBT) self-assembled monolayer (SAM) treatment on the Au source/drain contact for bottom-contact (BC) OTFTs with 4H-21DNTT as an organic semiconductor and Parylene C as an organic gate dielectric was systematically analyzed. The interface properties were characterized by AC3, X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), contact resistance, and trap state analysis. The results showed that with PFBT SAM and UV–O3 treatment, the OTFT performance was significantly improved, while on increasing the UV–O3 exposure time from 3 to 7 min, the threshold voltage shifted from 1.2 to 4.6 V. It was observed that due to UV–O3 exposure, the interface traps were induced, as chemical groups (C–O) were formed in underlying Parylene C. The best mobility of 11.39 cm2 V–1 s–1 was obtained for 4H-21DNTT OTFT with UV–O3 (3 min exposure) + PFBT Au surface treatment. The results demonstrate that a simple UV–O3 and PFBT interface treatment has a substancial effect on the properties of the metal/organic interface and the underlying dielectric surface. Thus, the regulation of the UV-O3 exposure duration gives a way to modulate the OTFT parameters.