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As power sources for Internet-of-Things sensors, thermoelectric generators must exhibit compactness, flexibility, and low manufacturing costs. Stretchable and flexible painted thermoelectric generators were fabricated on Japanese paper using inks with dispersed p- and n-type single-walled carbon nanotubes (SWCNTs). The p- and n-type SWCNT inks were dispersed using the anionic surfactant of sodium dodecylbenzene sulfonate and the cationic surfactant of dimethyldioctadecylammonium chloride, respectively. The bundle diameters of the p- and n-type SWCNT layers painted on Japanese paper differed significantly; however, the crystallinities of both types of layers were almost the same. The thermoelectric properties of both types of layers exhibited mostly the same values at 30 °C; however, the properties, particularly the electrical conductivity, of the n-type layer increased linearly, and of the p-type layer decreased as the temperature increased. The p- and n-type SWCNT inks were used to paint striped patterns on Japanese paper. By folding at the boundaries of the patterns, painted generators can shrink and expand, even on curved surfaces. The painted generator (length: 145 mm, height: 13 mm) exhibited an output voltage of 10.4 mV and a maximum power of 0.21 μW with a temperature difference of 64 K at 120 °C on the hot side. [ABSTRACT FROM AUTHOR]

To produce electricity via photothermoelectric effects, single-walled carbon nanotubes (SWCNT)-thermoelectric generators (TEGs) featuring different Seebeck coefficient distributions across pn-junctions are fabricated using vacuum filtration. In general, it is difficult to regulate the patterning area with wet processes as the dispersion tends to diffuse laterally into the SWCNT sheet. However, we modify the conditions of vacuum filtration, and the change rates of Seebeck coefficient across the pn-junction can be controlled from 2.5 to 8.3 μV/(K·mm). Temperature gradients are generated in the SWCNT-TEGs when artificial sunlight is applied to irradiated and non-irradiated areas. The SWCNT-TEG with a steep Seebeck coefficient distribution (8.3 μV/(K·mm)) exhibits at an output voltage of 1.5 mV, which is three times higher than that of the SWCNT-TEG with gradual Seebeck coefficient distribution. These results lead to improve the performance of SWCNT-TEGs for energy harvesting. [Display omitted] • Photothermoelectric effects have been investigated using SWCNT films. • Flexible SWCNT-TEGs with a pn-junction were prepared by vacuum filtration. • Rates of change of the Seebeck coefficient across the pn junction can be controlled. • SWCNT-TEG with a steep Seebeck coefficient distribution exhibits high output voltage. • The results lead to improved performance of SWCNT TEGs for energy harvesting. [ABSTRACT FROM AUTHOR]