Surface Etching of Polymeric Semiconductor Films Improves Environmental Stability of Transistors

Solution-processed polymeric semiconductor films are attracting wide interest for applications in flexible electronics, wherein environmental stability is still a big obstacle. In many polymeric thin-film electronic devices, vertical phase separation has been observed, which leads to film depth dependences of electronic properties. Here, a soft plasma-assisted surface etching method to improve the environmental stability and maintain the electronic properties of organic field-effect transistors (OFETs) is proposed, by which the unwanted thin-film surface (exposed to air) is selectively taken away upon soft plasma etching, and the layer beneath the surface (subsurface) is preserved without any damage to the subsurface’s structure or electronic function. Investigation of frequently used polymeric semiconductors poly(3-hexylthiophene) and poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4b′]dithiophen-2-yl)-alt [1,2,5]thiadiazolo[3,4-c]pyridine] shows that the crystallinity of the surface layer is higher than that of the subsurface layer. However, for p-type polymeric semiconductors, higher crystallinity usually leads to a lower ionization energy and higher doping concentration during exposure to air and thus a higher background conductivity, deteriorating the switching-off capability of the organic field-effect transistors (OFETs). Therefore, by removing this surface layer, the lifetime of OFETs in air is effectively increased by over 50%.