Conversion of Solar Energy into Electrical Energy Storage: Supercapacitor as an Ultrafast Energy‐Storage Device Made from Biodegradable Agar‐Agar as a Novel and Low‐Cost Carbon Precursor

Solar cells hold promise as energy conversion devices but intermittent sunlight limits their continuous applications. The self‐powering integrated solar cells and electrical energy storage devices can be an alternative to resolve this problem. This study demonstrates the integration of solar cell with supercapacitor (SC) device and evaluates its performance for energy conversion and storage for practical validity. SC carbon is derived from agar‐agar as low‐cost carbon precursor and a high‐performance SC electrode is utilized for the first time. The fabricated SC shows an excellent specific capacitance of 170 F g(−1) and retains 85% of its original value up to 15 000 charge/discharge cycles at 1 A g(−1), and it holds a maximum energy density of 17.7 Wh kg(−1). The integration of SCs (three cells in series with 5.4 V) with a commercial solar lantern for a self‐sustaining power pack is demonstrated. The SC is charged by solar cells in a few seconds and powers a solar lantern with 40 light‐emitting diodes without sunlight, demonstrates its potential for efficient conversion of solar energy into electrical energy storage. This result highlights that solar SC can be considered as an ultrafast next‐generation energy‐storage device that can mitigate the energy demand in the near future.