SOLAR ENERGY: RAIN, HAIL OR SHINE
08 May 2018
As useful and ubiquitous as solar energy is becoming, it still has one major hurdle: rain. A team of Chinese engineers have developed a hybrid solar cell that produces electricity come rain or shine, providing a sustainable solution for climates across the world.
A team of Chinese engineers have developed a hybrid solar cell that can produce electricity 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, otherwise known as static electricity. It has the potential to be used to harvest energy from movement or vibrations through clothing, car wheels, floors or touchscreens.
The researchers tapped into the motion of raindrops rolling off the surface of a solar cell by adding 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). In order to improve their performance, both polymer layers are imprinted with the same pattern on the data side of DVDs to give them texture. 
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 has a peak short-circuit current of about 33 nA, and a peak open-circuit voltage of around 2.14 V. Although these numbers are not high, they do prove the concept and there is potential to scale up the idea in the future.
This isn't the first time researchers have experimented with TENGs to make solar cells more useful in adverse weather conditions, but this new device is a simpler design, less bulky and easier to manufacture than others.
