Cu₃Se₂/graphite (p-type) and β-MnO₂ (n-type)-based screen-printed flexible thermoelectric generator: Improved power factor through compositional tuning of graphite

An efficient electrical conductivity and minimal thermal conductivity of abandoned available, low-cost, and non-toxic copper chalcogenides, owing to their phonon-liquid electron crystal structure, has gained importance in the present work. The influence of graphite on the thermoelectric performance of flexible thermoelectric generators based on Cu₃Se₂/graphite hybrid composite ink as p-type and β-MnO₂ as n-type, fabricated using screen printing, is reported. The addition of 0.5–2 wt% of graphite has increased the bandgap of Cu₃Se₂ from 3.29 to 3.93 eV; along with that, fine grinding of the composites during ink preparation has resulted in the tuning of microstructure, which optimized the carrier mobility, carrier concentration and resulted in enhanced Seebeck coefficient and electrical conductivity. The maximum open circuit power output, power factor, and power density of a flexible thermoelectric generator consisting of 1.5 wt% of graphite in Cu₃Se₂ at a temperature difference of 100 °C were 184.0 nW, 76.67 nW/m²K², and 147.44 mW/m², respectively. These results are superior to previously reported works using novel materials. The simple and cost-effective method using sustainable materials explored in this work can be easily scaled up for mass production of the devices.