Transparent stretchable thermogalvanic PVA/gelation hydrogel electrolyte for harnessing solar energy enabled by a binary solvent strategy

Aqueous thermocells are environment-friendly power sources capable of converting low-grade thermal energy into electricity to power small electronics in various application scenarios free from batteries. However, its poor portability and transparency, mechanical fragility, and low output performance impose a burden on its extensive application. Here, we demonstrate a highly transparent, flexible and stretchable gel with the cross-linked PVA/gelation double network frame by introducing DMSO/water binary solvent to suppress the formation of hydrogen bonds along the three dimensional directions, forming numerous microcrystalline regions. When the temperature difference is 40 K, the gel-based thermogalvanic cell achieves an open-circuit voltage of about 63 mV with the maximum power density of about 1.2 mW m-2. By implanting a PDMS solar absorber, the assembled solar thermoelectric gel device delivers a maximum temperature difference of about 11.2 K with an open-circuit voltage up to 16.6 mV and short-circuit current of more than 100μA, respectively, upon exposure to sunshine over 12 h. This work may provide new ideas for harnessing ambient heat and solar energy to electrical energy conversion.