A solar cell’s efficiency is defined through its capacity to convert as much as possible from the light spectrum into electricity, or,otherwise said, the solar cell has to have a wide range of energy bandgaps.
Cun-Zeng Ning and Alian Pan, from Arizona State University, have discovered and fabricated the first quaternary semiconductor nanowire materials, by alloying two binary semiconductors (ZnS + CdSe) – Zinc Sulfide and Cadmium Selenide, and obtained ZnCdSSe.
By controlling the spatial variation of various elements and the temperature of the substrate (the dual-gradient method), the team has produced light emission ranging in wavelength from 350nm to 720nm on a single substrate just a few centimeters in size.
The color spread across the substrate can be controlled to a large degree, and Ning says he believes that the dual-gradient method can be more generally applied to produce other alloy semiconductors or expand the bandgap range of these alloys.
The use in photovoltaics, though, involves developing a lateral multi-cell design combined with a dispersive concentrator. The concept of spectral split concentration (or dispersion concentration) has been studied for decades, but until now typical applications use separate solar cells for each wavelength band.
By making a monolithic lateral super-cell containing multiple subcells, Ning hopes to build a material that can absorb the entire light spectrum, and thus to have a high efficiency with a low fabrication cost, every solar cell manufacturer’s dream.