Nanocrystals aid PV cell creation

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Single-junction solar cells that could reach efficiencies of 45 per cent are being developed with the help of nanocrystals by researchers at Glasgow University.

The work, being led by Prof Colin Stanley at the university’s department of Electronics and Electrical Engineering, centres around the use of quantum dot crystals to develop photovoltaic (PV) cells known as Intermediate Band Solar Cells (IBSCs).

In PV cells a proportion of the solar spectrum is unused because the semiconductor from which the cell is made is transparent to photons with energies less than its bandgap. A higher proportion of the solar spectrum can be absorbed by using a semiconductor with a small bandgap.

‘A cell made from this material will produce a lot of current, but at a low voltage,’ explained Stanley. ‘Conversely, if a wide bandgap semiconductor is employed, the output voltage will be high but the current will be low.’

In an attempt to address these trade-offs, the team at Glasgow has been working on a new type of PV based on III-V semiconductor quantum dots, which has the potential to outperform existing types of multi-junction III-VPVs.

According to Stanley, the IBSC can generate both high voltage and high current.

‘The structure is, in essence, simpler; it is a single-junction device and does not require the same degree of current matching to make it work efficiently, nor does it need tunnel diodes.’

Much of the physics that underpins the IBSC has been demonstrated by Stanley’s team at Glasgow University, in collaboration with colleagues at Universidad Politecnica de Madrid. Glasgow University has also recently spun-out the company, Solway Photovoltaics, to exploit the technology.