Solar cells made more efficient

Scientists have reported progress in photovoltaic research as they have improved a component that will enable solar cells to use more energy of the sun and thus create a higher current.

The improvement concerns a conductive oxide film that now has more transparency in the infrared region.

Similar attempts had been made before, but this is the first time that these films were prepared by a one-step process and, at the same time, stable in air.

"The films made at the University of Luxembourg have been exposed to air for one and half years and are still as conductive as when they were freshly prepared," said Susanne Siebentritt, head of the laboratory for photovoltaics at the University of Luxembourg.

"It is a fantastic result, not only for solar cells, but also for a range of other technologies," she added.

In solar cells the film has to be conductive because it constitutes the upper electrode. At the same time it has to be transparent in order for sunlight to reach the layer underneath, where the current is formed.

Transparent conductive oxides are used in any device combining electronics and light, like LEDs, solar cells, photo-detectors or even touch screens.

The oxides forming this film can be made conductive by deliberately adding impurities. Zinc oxide with aluminium added is a widely used example.

Now scientists have modified the process used to make the film in order to make pure zinc oxide more conductive.

"Our multi-disciplinary team had the idea to add an additional component - another gas plasma - in the so called sputter process. This makes the material conductive even without aluminium," explained Siebentritt.

This method enables to have less but faster moving free electrons.

"With this result, the conductivity is similar to the one with aluminium, but it enables a much better transparency which makes solar cells more efficient," said the researcher.

The findings were published in the journal Progress in Photovoltaics.