Photolithographic p–n patterning of single-walled carbon nanotube sheets using photobase generators

Abstract

Single-walled carbon nanotubes (SWCNTs) are promising thermoelectric materials because of their high electrical conductivity and Seebeck coefficient. To construct a thermoelectric generator (TEG) employing SWCNTs, the development of n-type regions within a single piece of p-type SWCNTs has gained interest, offering a seamless TEG structure without the need for metal electrodes to bridge the p- and n-type regions. Several patterning methods such as thermal deposition, plasma-induced degradation, and photoinduced doping have been put forward as potential substitutes for traditional drop casting owing to their straightforward processes and superior patterning resolution. In this study, a photobase generator (PBG) was utilized as an n-type dopant for photoinduced doping. The PBG-doped SWCNTs demonstrated exceptional thermal stability, retaining a p-type nature in the absence of UV irradiation, which, upon UV exposure, spontaneously transitioned to n-type. Moreover, the resulting n-doped region displayed remarkable stability in air for more than 100 days. Employing this technique, planar-type TEG devices with up to six p- and n-type regions in sequence were constructed. The TEGs exhibited an in-plane open-circuit voltage and maximum power output of 3.45 mV and 5.75 nW, respectively, when a temperature gradient of 30 °C was applied between the front and back sides of the sheets.