To study the fundamental energy storage mechanism of photovoltaically self-charging cells (PSCs) without involving light-responsive semiconductor materials such as Si powder and ZnO nanowires, we fabricate a two-electrode PSC with the dual functions of photocurrent output and energy storage by introducing a PVDF film dielectric on the counterelectrode of a dye-sensitized solar cell. A layer of ultrathin Au film used as a quasi-electrode establishes a shared interface for the I-/I3- redox reaction and for the contact between the electrolyte and the dielectric for the energy storage, and prohibits recombination during the discharging period because of its discontinuity. PSCs with a 10-nm-thick PVDF provide a steady photocurrent output and achieve a light-to-electricity conversion efficiency (η) of 3.38%, and simultaneously offer energy storage with a charge density of 1.67 C g-1. Using this quasi-electrode design, optimized energy storage structures may be used in PSCs for high energy storage density.
Keywords: Dye-sensitized solar cells; PVDF film; energy storage; self-charging.