Fabrication of low-cost flexible thermoelectric generator using conductive HB graphite paint operated by solar radiation

Abstract

Paper-based flexible thin film thermoelectric generators have emerged as a promising and feasible alternative to organic and inorganic conductors due to their ability to operate at room temperature within a limited temperature range. Here, a flexible solar thermoelectric generator (STEG) designed from a single material has been introduced, prepared by a simple painting method. We prepared HB graphite-based conductive paint and demonstrated a very unique method to design flexible STEG devices. The graphite paint shows p-type semiconductive behaviour, while, in conjunction with the polyethyleneimine (PEI) polymer, it acts as an n-type material. Based on the transport properties, the paint appears to be a good candidate for designing STEG devices. At room temperature, the power factor of 378 nW m−1 K−2 for p-type paint and 1.51 nW m−1 K−2 for n-type paint is obtained. In order to examine flexibility over the long term, the performance of the material was inspected through 300 repeated cycles, and transport properties (conductivity) were found to increase from 21 700 S m−1 to 73 500 S m−1 due to the excellent emulsifying properties of gum Arabic, which were confirmed by field emission scanning electron microscope analysis. To evaluate the performance of the thermoelectric (TE) generator, eight pairs of p–n legs are fabricated on normal copier (80 GSM) paper, and an output voltage of ∼0.1 mV K−1 (∼5.5 mV) for a temperature gradient T of up to ∼60 K was achieved. Further, the performance of flexible TE devices can be improved by increasing the number of thermoelectric legs and by sandwiching the device between Kapton tapes. Our work suggests a promising and simple approach to achieving cost-effective conversion of solar energy into electricity and highlights the potential of flexible STEGs for low-power applications.