Monolithic Self-Charging Storage Device with Stable 3 V Operation

Abstract

Monolithic self-charging storage device with Stable 3 V Operation The energy paradigm has been changing from the traditional power plant system to micro-gride system based on renewable energy. However, renewable energy including wind, solar, and vibration, is intermittent and influenced by time, weather, and location. Thus, the suitable storage device is required for efficient utilization of renewable energy. The representative combination of renewable energy and energy storage device is an energy storage system (EES) consisting of photovoltaic systems and Lithium-ion batteries. The EES is mainly applied to social infrastructure system that generate large amounts of energy. As the Fourth Industrial Revolution progresses, the rechargeable power supply including Lithium-ion batteries is widely applied to wireless system such as sensor network, wearable device, and electric vehicles. However, the batteries have only storage function, so periodic charging is required. Thus, it is necessary to develop technologies for portable and small energy generation/storage as standalone power sources that can continuously supply power to various electronic devices. Large-scale energy production/storage system has entered the maturity stage, but the development of portable and small energy generation/storage systems based on IoT is in its early stages. To date, research on this system is conducted by simply connecting energy harvesting and energy storage device to external wires after manufacturing them independently. However, the introduction of additional wires is complicated in system design and manufacturing and has difficulty in miniaturization. These problems have motivated the integration of both functions into one device. The integrated device is fabricated by sharing one electrode, called a common electrode between the energy harvesting and storage components. Currently, research on a monolithic photo-charging storage device that integrates solar cells and energy storage devices into one device has been developed. This structure can miniaturization and flexible design, thereby it is suitable for the wearable and smart device. Although the importance of an integrated device is emphasized, the current research of monolithic device is limited to the fabrication of an integrated device without considering their practicability. In other words, most studies focus on simply connecting two devices to achieve the highest overall efficiency. In this case, since the open circuit voltage of single solar cell is under 1 V, the operation of photo-charging storage device is limited to 1 V. Thus, we proposed the monolithic photo-charging storage device operating at 3 V. We fabricated the multiple series-connected perovskite solar cell to increase the operating voltage. Since the secondary batteries are difficult to be charged by the high current density of 20 mA cm−2 solar cell owing to their storage mechanism, we choose the supercapacitor with the rapid response to an applied electric field change. We select the silver paste as the common electrode owing to its strong adhesion, high electric conductivity, and lack of chemical/mechanical damage to the solar cell and supercapacitor. Based on density functional theory (DFT) calculation, we prove the common electrode exhibits good compatibility with our supercapacitor and solar cell. For this reason, the proposed photo-charging storage device exhibits an ultra-fast charging time of less than 3 sec under AM 1.5 G illumination and high overall efficiency of 13.17 % at 1 mA cm−2 and 9.87 % at 20 mA cm−2. For electric double layer supercapacitors integrated with a solar cell, higher discharging current densities that 20 mA cm−2 have not been reported so far. We firstly demonstrate the behavior of photo-charging storage device under light/dark state by the impedance analysis. By the impedance analysis, we demonstrated that the solar cell provides a stable power supply to the supercapacitor under light condition. Further, the additional encapsulation ensures the long-term stability of photo-charging storage device and demonstrate the indoor cycling performance. We prove the photo-charging storage device has high potential as an IoT sensor power source. Figure 1