Nanowires to improve solar cells, LEDs

A group of researchers at Arizona State University claim that their work will lead to better photovoltaic cells and improved light emitting diodes (LEDs).

Cum Zheng Nim and Allan Pan said they will improve quaternary alloy semiconductor nanowire materials.

Quaternary alloys are made of semiconductors with four elements, quite often by making alloys of two or more compound semis.

The engineers aim to increase band gaps for both PV cells and LEDs. In theory you get the best solar cell efficiency by matching the entire solar spectrum for photovoltaic cells.

And if you have better band gaps in LEDs, that means more colours can be emitted from the semiconductors.

Making alloys of two or more semiconductors helps to increase the band gaps – but that needs a condition to exist called lattice constant matching.

The research team at Arizona alloyed two semiconductors – zinc sulphide (ZnS) and cadmium selenide (CdSe to produce a quaternary alloy ZnCdSSe and that gives continuously varying composisions of elements on one substrate.

That, claims the team, is the first time a quaternary semiconductor has been produce as a nanowire or nanoparticle – they’ve produced light emissions raning from 350 to 720 nanometres on one small substrate.

The next step for the engineers is to make a monolithic lateral super cell containing multiple subcells in parallel, with each one optimised for a given wavelength band.

It may be quite some time before the techniques reach the production stage.