Synergistic Interactions in Sequential Process Doping of Polymer/Single‐Walled Carbon Nanotube Nanocomposites for Enhanced n‐Type Thermoelectric Performance
Po‐Shen Lin, Jhih‐Min Lin, Shih‐Huang Tung, Tomoya Higashihara, Cheng‐Liang Liu
Abstract
Abstract This study focuses on the fabrication of nanocomposite thermoelectric devices by blending either a naphthalene‐diimide (NDI)‐based conjugated polymer (NDI‐T1 or NDI‐T2), or an isoindigo (IID)‐based conjugated polymer (IID‐T2), with single‐walled carbon nanotubes (SWCNTs). This is followed by sequential process doping method with the small molecule 4‐(2,3‐dihydro‐1,3‐dimethyl‐1 H ‐benzimidazol‐2‐yl)‐ N , N ‐dimethylbenzenamine (N‐DMBI) to provide the nanocomposite with n‐type thermoelectric properties. Experiments in which the concentrations of the N‐DMBI dopant are varied demonstrate the successful conversion of all three polymer/SWCNT nanocomposites from p‐type to n‐type behavior. Comprehensive spectroscopic, microstructural, and morphological analyses of the pristine polymers and the various N‐DMBI‐doped polymer/SWCNT nanocomposites are performed in order to gain insights into the effects of various interactions between the polymers and SWCNTs on the doping outcomes. Among the obtained nanocomposites, the NDI‐T1/SWCNT exhibits the highest n‐type Seebeck coefficient and power factor of −57.7 µV K −1 and 240.6 µW m −1 K −2 , respectively. However, because the undoped NDI‐T2/SWCNT exhibits a slightly higher p‐type performance, an integral p–n thermoelectric generator is fabricated using the doped and undoped NDI‐T2/SWCNT nanocomposite. This device is shown to provide an output power of 27.2 nW at a temperature difference of 20 K.