Integrated solar cells and supercapacitor: a self-rechargeable power source for Internet of Things devices

The rapid development of low-power connected devices, widely used in fields like the Internet of Things, building automation, smart agriculture, and wearables, is opening up new opportunities for unconventional use of photovoltaics. Usually, these devices need to be powered locally and without any wire connection, therefore rechargeable or disposable batteries are used. Batteries are a reliable energy source, but the need of periodically recharging or replacing them can become a limitation in terms of user friendliness or maintenance costs, hindering the development of large, connected sensor networks or resilient systems. In these cases, integrating energy harvesting and energy storage technologies in self-rechargeable units can enable self-sufficient, maintenance free low-power devices. In this context, third generation photovoltaics such as dye-sensitized solar cells and perovskite solar cells are proving to be excellent solutions to efficiently harvest energy in non-conventional lighting conditions such as indoor illumination and diffused sunlight. Moreover, they can be easily integrated with supercapacitors thanks to custom device architectures and shared active material, providing compact hybrid self-rechargeable energy sources. Indeed, supercapacitors, despite having lower energy density than batteries, are intrinsically more suitable to be integrated with solar cells thanks to their higher cycling stability and lower sensibility to charging current variation and working voltage. In this contribution, we demonstrate a self-rechargeable energy unit obtained by the integration of a dye-sensitized solar module and a high voltage supercapacitor, fabricated on the same current collector with shared fabrication steps. The integrated device is successfully tested in real life indoor conditions to continuously power a temperature and humidity sensor, demonstrating the compatibility of this technology as a complementary power source in battery powered electronic devices.