Periodic Reporting for period 1 - STORE-LIGHT (Photoelectrodes that STORE LIGHT energy)
Reporting period: 2024-03-01 to 2025-08-31
Solar energy is not constant and hence an unstable power source owing to its intermittent nature. Therefore, storage of solar energy is an important issue. Our new technology combines solar energy conversion and storage into one, thus delivering the opportunity to exploit the benefits of solar energy conversion also beyond the availability of sunlight. The objectives offered by STORE-LIGHT are the development of photo-storage electrodes and ultimately devices and micro-devices for the storage of photon energy. The development of integrated solar-to-charge storage systems are of major importance to exploit the full potential of solar energy, and in the same time extending the limits of conventional energy storage systems. A photo-responsive storage system as planned in STORE-LIGHT, achieving direct and seamless solar energy conversion and storage in one single compact architecture, would be a transformative approach to power off-grid devices.
Such unique photo-to-charge storage technology will ultimately affect extended application areas such as self-powered sensors or the next-generation in micro-electronics and IoT.
Such unique photo-to-charge storage technology will ultimately affect extended application areas such as self-powered sensors or the next-generation in micro-electronics and IoT.
Our major goal of STORE-LIGHT is to develop a fully functional stand-alone photo-storage system that can be used to drive external devices. Towards this aim we have employed semiconductor metal oxide (MO) nanocrystals (NCs), such as indium tin oxide (ITO) NCs as light-harvesting and energy-storing materials. We first prepared and characterized them on a small scale. After synthesizing these structures, we analyzed their optical response through spectroscopic techniques. These doped materials can absorb UV light (above the band gap) and store photogenerated electrons, a phenomenon known as photodoping, which lies at the core of our project. We then focused on understanding the mechanisms behind charge accumulation and ways to improve it. To enhance the electron storage ability of ITO NCs, we explored the use of specific hole scavengers. Next, we produced electrodes as thin films based on ITO NCs using different solution-processing deposition techniques. We then integrated a sensitizers with the ITO NCs electrodes to extend their absorption into the visible light range. Finally, we prepared hybrid structures combining ITO NCs and the sensitizer, and characterized their capacitance under light and dark conditions using photo-electrochemical methods. The prepared photoelectrodes were used as working electrodes to fabricate two terminal photocapacitors with a simple design. Device performance under solar illumination was evaluated using photoelectrochemical techniques like cyclic voltammetry (CV) and galvanostatic charge discharge (GCD). These tests showed the MO layer increased capacitance by about 56% compared to the blank device, with illumination boosting it from 30% to 70%, reaching 10-19 µF/cm². To measure charges truly photostored, we applied the light charge–resistor discharge (LCRD) method, resulting in a specific capacitance of 4.5 µF/cm². Our results demonstrate functional photo-electrodes integrated into photo-supercapacitor-like devices for future solar energy technologies.
Typical solar energy conversion and storage devices to date couple solar cells, used as the energy conversion unit, to a super-capacitor or battery as the energy-storage unit. These photo-responsive storage systems exploit the photo-excited electrons and/or holes to drive the redox reactions of the batteries during charging and/or discharging processes. Energy-level matching between the light converting semiconductors and the redox species contained in the redox battery is critical, typically a three- or a four-electrode configuration is required, overall making the system bulky, non-versatile and expensive. Therefore, the combination of both processes of photon-energy conversion and storage into the same photo-storage electrode as targeted by STORE-LIGHT is an innovative approach towards the more efficient, compact and cost effective use of solar energy. Moreover, we will use elements that are derived from non-critical raw materials, relying on elements such as zinc, iron, tin, indium (removed from the list of critical raw materials in 2023) and oxygen.