Multilayer Device Delivers Solar and Raindrop Energy Harvesting

Let’s face it: Energy harvesting of all types generates significant interest and attention, as it has that aura of getting a little bit of something – electrical energy – for almost nothing in cost. Usually, it functions silently and endlessly (in most cases). Moreover, it can eliminate the need for a product to include its own fixed-life source or charge one from an outside energy source. What’s not to like?

Reality is that many of these harvesting schemes turn out to be impractical for various reasons, including very low harvested-energy density as judged by various metrics. Further, most harvesting schemes can only extract energy from a single physical phenomenon such as light, vibration, friction, airflow, or ambient RF, to cite some well-known options.

Perovskite Plus Triboelectric Nanogenerators

Now, a research team at the Institute of Materials Science of Seville (ICMS), a joint center of the Spanish National Research Council (CSIC) and the University of Seville (US), have created a single hybrid-function device that can generate energy from both sunlight and rainfall (Fig. 1). Their energy-harvesting system, which combines perovskite solar cells (PSCs) with drop-driven triboelectric nanogenerators (D-TENGs), offers an interesting approach to more effective power harvesting under diverse conditions.

Key to the harvester operation is its patented thin film that protects perovskite solar cells and improves their durability, even in harsh weather. These fluorinated polymer (CFₓ) films function as multifunctional encapsulation layers that simultaneously provide water resistance, triboelectric functionality, and optical transparency (>90 %). The same film nanogenerators also produce more than 100 V — admittedly at very low current — from the impact of a single raindrop.

One major challenge with perovskite cells is their tendency to degrade under environmental stress; this has been a limitation to their expanded use. To address this limitation, the ICMS team used plasma technology to deposit a protective coating about 100 nm thick onto the cells.

This coating serves two key roles. It acts as a protective layer that shields the material chemically while also enhancing its ability to absorb light. At the same time, it has a triboelectric surface (which generates electrical charge through friction or contact) that converts the energy of falling raindrops into usable electricity.

Test and Evaluation of the Harvester and Its Coating

The team performed a list of ruggedness tests on the coating with impressive results. They also ran tests and compiled data on solar- and raindrop-driven harvesting performance (Fig. 2).

They also built a self-charging prototype with a custom boost converter to drive an LED array and demonstrate the practicality of this multisource energy harvesting for low-power electronics. It delivered open-circuit voltage peaks up to 110 V and a maximum power density of ~4 mW/cm2 under rainwater droplets, while retaining over 85% of its initial output after more than 17,000 droplet impacts.

The hybrid PSC/D-TENG device achieved short-circuit current densities of 11.6 mA/cm² under 0.5 sun illumination and peak voltages of 12 V per raindrop, enabling simultaneous solar and rain energy harvesting.

The device maintained 80% of its initial performance after 300 hours of continuous illumination under humid conditions and demonstrated stability under continuous dripping and illumination for more than five hours. This drop-driven triboelectric nanogenerator offers an intriguing solution for continuous power generation under diverse weather conditions.

Now if they also combined it with a nighttime radiant-energy harvester, they would have a triple-threat device.

Details of their work, including setup, implementation, materials, test arrangements, and results are in their lengthy paper “Water-resistant hybrid perovskite solar cell - drop triboelectric energy harvester” published in Nano Energy.