Despite continual improvements in efficiency, silicon-based solar cells are hampered by the fact that they only deliver power when the sun is shining and that their efficiency falls off markedly at temperatures over 100° C (212° F). To address these limitations, scientists at TU Wien in Vienna have combined perovskite-based solar cells that work at high temperatures with an electrochemical cell that allows the energy from ultraviolet light to be stored chemically.
Unlike a conventional cell, which converts light directly to electricity, the TU Wien system uses UV light to directly pump oxygen ions through a solid oxide electrolyte. According to the team, in operation the pump produces an open-current voltage of up to 920 millivolts at a temperature of 400° C (848° F). It achieves this high temperature capability by swapping out the silicon-based photovoltaics with perovskites, which have shown tremendous potential in solar cell applications.
Georg Brunauer, whose doctoral thesis work while a student at TU Wein the research is based, says this would allow the solar cells to be used in large scale plants that concentrate sunlight onto the cells using mirrors while maintaining high conversion efficiency.
“Our cell consists of two different parts – a photoelectric part on top and an electrochemical part below,” says Brunauer. “In the upper layer, ultraviolet light creates free charge carriers, just like in a standard solar cell. The electrons in this layer are immediately removed and travel to the bottom layer of the electrochemical cell. Once there, these electrons are used to ionize oxygen to negative oxygen ions, which can then travel through a membrane in the electrochemical part of the cell. This is the crucial photoelectrochemical step, which we hope will lead to the possibility of splitting water and producing hydrogen.”
According to Brunauer, the system is capable of being scaled up and with a slight increase in electrical power production it can go from merely pumping oxygen ions to splitting water into hydrogen and oxygen. In addition, it could even be used to split carbon dioxide into carbon monoxide. In this way, it could be used to not only generate electricity, but also to synthesize fuels.