Recent Advances in Doping Strategies for N-type Carbon Nanotube-Based Thermoelectric Materials

The quest for high-performance, flexible thermoelectric (TE) materials has spurred considerable interest in carbon nanotube (CNT)-based systems. Efficient CNT based devices require both p- and n-type CNT-based TE materials, however, the performance and stability of n-type CNTs are far behind those of p-type. Effective n-type doping strategies are crucial for advancing the development of CNT-based TE materials. This review comprehensively summarizes recent advances in n-type CNT-based TEs, covering the structure-performance relationship, n-type doping strategies, and stability issues and strategies. The doping strategies are systematically summarized and categorized into alkali/alkaline earth metals, organic dopants and ionic dopants. More importantly, the mechanisms, advantages, and limitations of each doping avenue are thoroughly analyzed to offer guidance for developing high-efficiency n-type CNT-based TEs. In addition, the intrinsic instability issues of n-type CNTs are carefully discussed alongside emerging solutions, including various encapsulation methods and the intrinsic self-protection mechanisms of CNTs. Finally, the discussion extends beyond material synthesis to device-level integration, expounding how these chemical strategies can enhance output performance and mechanical durability in power generation modules. Through the systematic analysis spanning structure-property correlations, doping strategies, comparative studies, and stability assessments, the review aims to highlight the most promising directions for achieving long-term robust and high-performance n-type CNT-based TEs. The insights presented herein are expected to catalyze further innovation and accelerate the evolution of CNT-based TEs for next-generation energy harvesting applications.