Flexible wearable thermoelectric generator with vertically aligned architecture of pedot pss and carbon nanotube films

Abstract

Energy harvesting has become pivotal for wearable electronics, which require a constant power supply. Recent research has paved the way for the development of a wide variety of self-powered devices that harvest energy from the human body. Thermoelectric generators (TEGs) facilitate maintenance-free sustainable energy transduction, making them an enticing and feasible option for harvesting energy. Notwithstanding, their energy conversion process suffers because of inadequate design and rigidity owing to the use of brittle and toxic inorganic material-based thermoelements, making them inappropriate for energy harvesting from the human body. To address the issues, flexible wearable TEGs have been developed by integrating flexible conducting polymer based thermoelements. Nonetheless, their performance suffered significantly due to the deficient TEG designs, where thermoelements were integrated into the lateral layout with cross-plane heat flow direction. The design and implementation of such lateral TEGs is challenging for harvesting energy from the human body, where the temperature gradient (ΔT) lies between the body heat and the ambient temperature. Thus, developing a vertical structured TEG with flexible thermoelements with high deformability is a requisite. In this thesis, novel wearable TEGs with vertically aligned architecture of thermoelements based on flexible organic poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) and single-wall carbon nanotube (SWCNT) films were designed and fabricated. Finite element analysis was performed to analyze the heat dissipation through the thermoelements as well as to optimize their length for the highest ΔT and enhanced output performance. Thermoelements were prepared via solution-processing and drop-cast techniques, while the overall architectures of the TEGs were developed through low-cost 3D printing followed by a sacrificial molding technique. Flexible polydimethylsiloxane was used to develop TEG structures and encapsulation layers for all the thermoelements. The structures possess a high degree of flexibility and can sustain a maximum bending angle of 52 degrees without significantly changing their electrical parameters. In addition, this thesis examined the effects of acid-based post-treatments and polyethylenimine concentration on the performance of the thermoelectric properties of PEDOT:PSS and SWCNT films, respectively. As a proof of concept, a TEG was initially developed using five pairs of p-type PEDOT:PSS film and n-type aluminum wire-based thermoelements that produced an open-circuit voltage (Voc) and output power density (Pd) of 1.46 mV and 1.5 nWcm-2, respectively, at a ΔT of 11.27 °C from the wrist. Likewise, another TEG was composed of five pairs of p-type PEDOT:PSS and n-type SWCNT film-based thermoelements that generated a Voc and Pd of 1.75 mV and 10.17 nWcm-2, respectively, at a ΔT of 11.24 °C from the wrist. The proposed design approaches represent a significant step toward developing next-generation flexible organic TEG that could pave the way for self-powered wearable electronics in a sustainable way by utilizing the body heat.