Bicyclic-ring base doping induces n-type conduction in carbon nanotubes with outstanding thermal stability in air

Abstract

The preparation of air and thermally stable n-type carbon nanotubes is desirable for their further implementation in electronic and energy devices that rely on both p- and n-type material. Here, a series of guanidine and amidine bases with bicyclic-ring structures are used as n-doping reagents. Aided by their rigid alkyl functionality and stable conjugate acid structure, these organic superbases can easily reduce carbon nanotubes. n-Type nanotubes doped with guanidine bases show excellent thermal stability in air, lasting for more than 6 months at 100 °C. As an example of energy device, a thermoelectric p/n junction module is constructed with a power output of ca. 4.7 μW from a temperature difference of 40 °C.

Outstanding Robust Photo- and Thermo-Electric Applications with Stabilized n-Doped Carbon Nanotubes by Parylene Coating

“…Although there are several reports on n-dopants, their stabilization and degradation mechanisms have not been elucidated in detail. − Therefore, we aim to clarify the factor that governs n-dopant degradation by measuring the transient response of the thermo-electric properties of n-doped CNTs under various conditions. Figure depicts the fundamental properties of the n-doped CNTs used in this experiment.…”

“…Hole (p-type) or electron (n-type) injection can be controlled by the molecular structure. To enhance the performance of photo-thermo-electric devices, p–n junctions are typically utilized to increase the alternative Seebeck coefficient of materials; therefore, as a pristine state under air conditions, n-dopants for p-CNTs are particularly important and have been developed in various methods, such as polyethyleneimine, nitrogen-containing molecules, , amidine-based molecules, imidazolium salts, − and supramolecular complexes. , However, the critical problem of the n-doped stability in air remains because the CNTs gradually accept holes from oxygen molecules (oxidations) in air and are dedoped to p-type in several days up to months. Furthermore, although the features of these dopants, which are soluble in water and alcohol, make it easy to fabricate devices, they have the disadvantage of impeding the wearable and outdoor use of CNT devices.…”

Solution processed organic thermoelectric generators as energy harvesters for the Internet of Things

“…Some of the most widely studied and commercially available high performing n-type dopants include [73][74][75] and 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD). 76,77 Other n-dopants, such as triaminomethane (TAM) 68,78 and 1,3-dimethylimidazolium-2-carboxylate (DMImC), 70,78 have a smaller molecular volume and improved miscibility with the host, but these are not commercially available at high purities. In general, n-type dopants tend to demonstrate low doping efficiencies, sometimes falling below 1% 64,79 which can be prohibitive for TEGs, but strategies like functionalization of the dopant or host to improve miscibility 80,81 and processing techniques 67,82,83 have been shown to improve the doping efficiencies.…”

Advances in Thermoelectric Composites Consisting of Conductive Polymers and Fillers with Different Architectures

“…Therefore, to promote the development of the organic thermoelectric field, it is urgent to strengthen the development of high-performance n-type organic TE materials. For this plight, CNTs seem to be a great solution; however, CNTs and their composites are usually p-type in the ambient conditions without chemical treatment, n-type CNTs and composites doped with redox dopants are easily oxidized in the air, and the Seebeck coefficient becomes positive again gradually [ 76 , 77 , 78 ]. Against all odds, some progress was achieved through the unremitting efforts of researchers.…”