Energy harvesting and storage by indoor light using dye-sensitized solar battery (DSSB)

Abstract

Photo-rechargeable batteries (PRBs) have been developed as all-in-one energy devices having a merit that both energy harvesting and storage are realized in a single device. A major portion of the PRBs are based on non-faradaic processes (capacitive PRBs) for their energy storage. On the other hand, several works have focused on using faradaic processes (faradaic PRBs) because the faradaic PRBs are much superior in terms of energy densities. However, for the spontaneous electron transfer between the photo-electrode and the storage-electrode, the energy levels of the two active materials should be matched well, so that there are not so many storage materials having faradaic reaction. In addition, dim-light performances of the faradaic PRBs have not been reported as far as we know. Herein, we present an external-power-free single-structured faradaic PRB, named dye-sensitized solar battery (DSSB), developed specifically for indoor light harvesting. The DSSB was designed to be photo-charged by the photo-anodic process of dye-sensitized solar cells (DSSCs) and the cathodic process of LiMn2O4 (LMO). Redox mediators in electrolyte of the compartment to the photo-electrode are oxidized to regenerate activated dye molecules. The charged DSSB can be discharged by returning to their original state of the two redox active materials. The performances of DSSBs were strongly dependent on the thermodynamic and kinetic parameters of redox mediators. At one sun condition, the kinetics of mediator determined the light-to-charge energy efficiency (ηoverall). A kinetically-fast but thermodynamically-unfavorable (can make smaller cell voltage) mediator (I-/I3-) showed the best results in terms of photo-charging current (JCh) and discharge capacity (QdCh). However, in dim-light condition (200 ~ 2000 lux), a thermodynamically-favorable (can make larger cell voltage) mediator (Cu+/2+(dmp)2) delivered the highest photo-charging energy density (EDCh) corresponding to ηoverall of 11.5 % because kinetic limitation becomes negligible. The successful demonstration of the DSSB to operate an IoT sensor node only by an indoor light (500 lux) opens the possibility of realizing indoor-light-harvesting PRBs.