Co-Filtered Versus Carbon-Paste-Bonded p–n Junctions in Cold-Source-Free Single-Walled Carbon Nanotube Thermoelectric Generators

Single-walled carbon nanotube (SWCNT) p–n junction thermoelectric generators develop an in-plane temperature difference under uniform heating. They convert it into a voltage with no cold source. This suits maintenance-free Internet-of-Things sensors. Two routes form such a junction and differ in how each region is processed, so which junction property governs the output has remained open. Here we compare a co-filtered route, which couples the p- and n-type regions in a single wet process, with carbon-paste bonding of two separately filtered films. A hyperbolic-tangent fit resolves each Seebeck profile into a transition width and a total Seebeck coefficient ΔS. Bonding preserves the intrinsic p-type coefficient. It raises ΔS from 76 to 98 µV/K and narrows the transition from 7.7 to below 3.5 mm. The internal resistance rises by 36–42%. On infrared-transparent cycloolefin polymer, the effective in-plane temperature difference differed by only 9% between the routes. The 29% gain in ΔS transferred directly to the output, 0.42 against 0.30 mV. The maximum power rose from 0.47 to 0.65 nW. The total Seebeck coefficient therefore sets the output. Bonding offers higher output and printable scalability; the co-filtered route offers a jointless film, higher electrical conductivity, mechanical robustness, and simpler processing.