Realizing high energy density supercapacitors assisted by light-induced charging

The increasing demand for energy storage devices has initiated research on alternative sustainable energy storage mechanisms, such as supercapacitors. Here, we report a skillful design strategy that harvests visible light energy and has immense potential applications in boosting the storage capacity of supercapacitors - one of the energy storage devices. A down-conversion phosphor layer is introduced over a reduced graphene oxide-based supercapacitor electrode having an optical window to harvest visible light. The fabricated cell exhibits an excellent areal energy density of 233 mu Wh/cm2 (at an areal current density of 4 mA/cm2 for the voltage ranging from 2 to 4.25 V) under optical illumination, which is 2.5 times higher than that achieved without illumination. Under light illumination, the cell operates across a high voltage range (0-4 V) and current density (40 mA/cm2) and shows a light-induced charging voltage of 354 mV, without any external bias. Thus, such exceptional supercapacitor performance generates significant possibilities for developing novel energy storage devices with high energy and power densities, through which portable devices can be charged using visible light.