As useful and ubiquitous as solar energy is becoming, it still has one major Kryptonite: gloomy weather. Now, a team of Chinese engineers has developed a hybrid solar cell that can produce electricity come rain or shine, using the triboelectric effect to harvest energy from the movement of raindrops on its surface.

Triboelectric nanogenerators (TENGs) create a charge from the friction of two materials rubbing together, which you may recognize as static electricity. It could find eventual practical uses in harvesting energy from movement or vibrations through clothing, car wheels, floors, or touchscreens.

In this case, the researchers tapped into the motion of raindrops rolling off the surface of a solar cell. To do so, they added two polymer layers to form a TENG on top of a photovoltaic cell. The top layer consists of a polymer called polydimethylsiloxane (PDMS), while the lower layer is made of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). To improve the performance of both layers, the polymers are first textured with grooves by imprinting them with the pattern from the data side of DVDs.

The hybrid solar cell uses layers of two polymers to harvest energy from raindrops as well, using the triboelectric effect ACS Nano

The top layer is activated when drops of water land on it and roll off, bringing the polymer into contact with the lower layer. The PEDOT:PSS film acts as a mutual electrode between the TENG and the solar cell, conducting energy from the former to the latter. To make sure the photovoltaic cell still functions when it's sunny, both polymer layers are transparent.

According to the team, the device had a peak short-circuit current of about 33 nA, and a peak open-circuit voltage of around 2.14 V. That's not particularly high, but it is enough to demonstrate that the concept works, and might be scalable.

This isn't the first time researchers have experimented with TENGs to make solar cells more useful in other weather conditions, but the team says the new device is a simpler design, less bulky and easier to manufacture than others.

The research was published in the journal ACS Nano.

Source: American Chemical Society