New Alloys Key to Efficient Solar Energy and Lighting

A recent advance by Arizona State University researchers in developing nanowires could lead to more efficient photovoltaic cells as well as better LEDs. ASU electrical engineers are working to improve quaternary alloy semiconductor nanowire materials.

Nanowires are tens of nanometers in diameter and tens of microns in length. Quaternary alloys are made of semiconductors with four elements, often made by alloying two or more compound semiconductors. Semiconductors are the material basis for technologies such as solar cells, high-efficiency LEDs for lighting, and for visible and infrared detectors.


Ideally, the highest solar cell efficiency is achieved by having a wide range of band gaps that matches the entire solar spectrum, said Cun-Zheng Ning, a professor in the School of Electrical, Computer, and Energy Engineering.

Ning said that in LED lighting applications, more available band gaps means more colors can be emitted, providing more flexibility in color engineering or color rendering of light. For example, different proportions of red, green, and blue colors would mix with different white colors. More flexibility would allow white color to be adjusted to suit various situations, or individual preferences.


According to the researchers, the hurdle is that every manmade or naturally occurring semiconductor has only a specific band gap.

One standard way to broaden the range of band gaps is to alloy two or more semiconductors. By adjusting the relative proportion of two semiconductors in an alloy, it’s possible to develop new band gaps between those of the two semiconductors. Accomplishing this requires a condition called lattice constant matching, which requires similar inter-atomic spaces between two semiconductors to be grown together.

“This is why we cannot grow alloys of arbitrary compositions to achieve arbitrary band gaps,” Ning said. “This lack of available band gaps is one of the reasons current solar cell efficiency is low, and why we do not have LED lighting colors that can be adjusted for various situations.”

In recent attempts to grow semiconductor nanowires with “almost” arbitrary band gaps, the research team led by Ning and Alian Pan, an assistant research professor, have used a new approach to produce an extremely wide range of band gaps.

They alloyed two semiconductors - zinc sulfide (ZnS) and cadmium selenide (CdSe) - to produce the quaternary semiconductor alloy ZnCdSSe, which produced continuously varying compositions of elements on a single substrate.






The new quaternary alloy nanowires with large wavelength span can also be explored for color-engineered light applications.


(Arizona State University)
