Stable photothermal conversion in single-walled carbon nanotube device with pn-junction under uniform sunlight irradiation

N -type single -walled carbon nanotube (SWCNT) films with high air stabilities have attracted significant attention for their potential application in SWCNT devices featuring pn-junctions for power generation. However, SWCNT devices must be locally heated or formed into suspended structures to generate a temperature difference and produce output power. In this study, pn-junction SWCNT films were fabricated via vacuum filtration and subsequently attached to a polyimide substrate, enabling the creation of SWCNT devices without the need for suspended structures. Upon uniform irradiation with artificial sunlight, the SWCNT device produced a stable output voltage and short-circuit photocurrent. A thermographic image showed the emergence of a temperature gradient originating from the center of the SWCNT film and extending to the edge of the polyimide substrate. This phenomenon can be attributed to the higher optical absorption of SWCNT films compared to that of polyimide substrates. Consequently, the diffusion of carriers within the device generated an electric potential difference. Therefore, the SWCNT device generated a temperature gradient and yielded output power under uniform sunlight irradiation. These findings may aid in the development of facile and flexible optical devices, including photodetectors and hybrid devices integrating solar cells.