p–n patterning strategies for single-walled carbon nanotubes for the fabrication of joint-free thermoelectric generators

Abstract

Single-walled carbon nanotubes (SWCNTs) exhibit exceptional electrical, thermal, and mechanical properties because of their one-dimensional electronic structure, making them promising materials for flexible thermoelectric generators (TEGs). Recent advances in molecular doping and device engineering have enabled joint-free TEGs in which p- and n-type regions are seamlessly formed within a continuous SWCNT film or fiber, thus eliminating interfacial resistance and improving mechanical robustness. Realizing such architectures requires precise spatial control of carrier polarity, driving the development of selective doping strategies, including solution processing, thermal evaporation, and plasma- or light-assisted dopant removal. This review highlights recent progress on these methods, with a particular focus on photo-induced electron doping using photobase generators (PBGs). In particular, PBG1, a representative PBG, enables mask-defined n-type conversion without damaging SWCNTs, provides excellent stability, and achieves micrometer-scale p–n patterning. The demonstrations of planar TEGs based on p–n-patterned SWCNTs confirm the feasibility of scalable, flexible thermoelectric devices. The remaining challenges include maintaining sufficient temperature gradients despite lateral heat spreading in SWCNT networks and ensuring long-term operational stability. Opportunities in dopant design, nanoscale junction engineering, and thermal management are also discussed as pathways toward practical SWCNT-based thermoelectric technologies. Photo-induced dopants are patterned onto SWCNT films through UV mask exposure, where local irradiation tunes the electronic states of the adsorbed species to generate defined p- and n-type regions. This photopatterning process creates seamless, joint-free p–n architectures within the SWCNT network, forming continuous pathways for charge transport. As a result, the patterned SWCNT films function as monolithic, junction-free thermoelectric materials suitable for constructing integrated SWCNT-based thermoelectric generators