Hollow cylindrical design could improve solar cells' efficiency

20 January 2012

‘We tweaked the traditional flat design for luminescent solar concentrators and made them into cylinders,’ said Prof Sayantani Ghosh of California University, Merced. ‘The results of this architectural redesign surprised us, as it significantly improved their efficiency.’

According to the university, luminescent solar concentrators are designed to absorb solar radiation over a range of colours and to re-emit it over a narrower range (for example, only red) — a process known as down-converting. This light is transported to solar cells for photocurrent generation. The quantum dots embedded in the concentrator are the materials that carry out this colour conversion.

The biggest advantage they offer over traditional solar cells is that they can work even in diffuse sunlight, such as on cloudy days. And, because of this, they do not need to directly face the sun at all times, eliminating the need for tracking mechanisms.

The main problem preventing luminescent concentrators from being used commercially is that they have high rates of self-absorption, meaning that they absorb a significant amount of the light they produce instead of transporting it to the PV cells.

The research team showed that the problem can be addressed by changing the shape of the concentrator. They discovered that a hollow cylindrical solar concentrator is a better design compared with a flat concentrator or a solid cylinder concentrator. The hollow cylinders absorb more sunlight while having lower self-absorption losses.

Ghosh said that the design enhances performance while using the same number of quantum dots and therefore could be cost effective, as well as suitable for integration onto vertical surfaces such as walls and windows.