Graphene solar cells can work in the rain

RESEARCHERS have developed solar panels coated with a layer of electron-rich graphene that can generate electricity from both sunlight and salt ions in rain water.

A team led by Ocean University of China in Qingdao, devised a method of producing electricity from solar panels during wet weather periods, which can normally disturb power availability for the required demand.

The structural properties of graphene allow electrons to move freely (delocalise), and make it a negatively-charged material when in solution. When rainwater falls onto the panel, the droplets contain positively-charged salt ions of sodium, calcium and ammonia, which can bind with the surface of the graphene layer.

The interaction results in a double-layer, or pseudocapacitor, which causes the potential energy difference between the positively- and negatively-charged layers is enough to drive the delocalised electrons into producing a voltage and current.

The team was able to generate electricity in the hundreds of microvolts range and achieve a solar-to-electricity efficiency of 6.5% from the prototype graphene panel. Current solar panels are able to achieve 20% efficiency.

The team tested the prototype by using a salted solution to simulate rain, and a thin-film photovoltaic cell called a dye-sensitised solar cell.

The primary challenge facing the team is the relatively low concentrations of salt ions in rainwater compared to the salt solutions prepared in the lab, which will make it difficult for the panel to produce large quantities of electricity.

The next step for the team will be to improve efficiency to reach commercially-viable levels. They are currently working on modifying the technology to handle a variety of ion mixtures that can be contained in rainwater.

The team hopes the results can be incorporated into future solar cell designs and open up new ideas for alternative electricity generating capabilities for solar cells –for example, harvesting energy from ambient heat and light for indoor cells.

Angewandte Chemie, DOI: 10.1002/anie.201602114