Wearable Photo‐Thermo‐Electrochemical Cells (PTECs) Harvesting Solar Energy

Abstract Solar induced thermal energy is a vital heat source supplementing body heat to realize thermo‐to‐electric energy supply for wearable electronics. Thermo‐electrochemical cells, compared to the widely investigated thermoelectric generators, show greater potential in wearable applications due to the higher voltage output from low‐grade heat and the increased option range of cheap and flexible electrode/electrolyte materials. A wearable photo‐thermo‐electrochemical cell (PTEC) is first fabricated here through the introduction of a polymer‐based flexible photothermal film as a solar‐absorber and hot electrode, followed by a systematic investigation of wearable device design. The as‐prepared PTEC single device shows outstanding output voltage and current density of 15.0 mV and 10.8 A m –2 and 7.1 mV and 8.57 A m –2 , for the device employing p‐type and n‐type gel electrolytes, respectively. Benefiting from the equivalent performance in current density, a series connection containing 18 pairs of p–n PTEC devices is effectively made, which can harvest solar energy and charge supercapacitors to above 250 mV (1 sun solar illumination). Meanwhile, a watch‐strap shaped flexible PTEC (eight p–n pairs) that can be worn on a wrist is fabricated and the realized voltage above 150 mV under light shows the potential for use in wearable applications.