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Materials Breakthrough Could Lead to More Efficient Solar Cells

16 October 2013

Researchers at Stanford University, the University of Illinois-Urbana Champaign and North Carolina State University have collaborated to create a heat-resistant thermal emitter that could significantly improve the efficiency of solar cells by using ceramic-type materials.

A typical solar cell has a silicon semiconductor that absorbs sunlight directly and converts it into electrical energy. Silicon semiconductors used in solar panels only respond to infrared light. Higher-energy light waves, including most of the visible light spectrum, are wasted as heat, while lower-energy waves simply pass through the solar panel.

Thermophotovoltaic systems, by contrast, send sunlight directly to the solar cell, through an intermediate component where the absorber heats up when exposed to sunlight, and the emitter converts the heat to infrared light, which is then beamed to the solar cell.

“This is a record performance in terms of thermal stability and a major advance for the field of thermophotovoltaics,” claimed Shanhui Fan, professor of electrical engineering at Stanford.

Unlike earlier prototypes that fell apart at temperatures below 2,200 degrees Fahrenheit (1,200 degrees Celsius), the new thermal emitter remains stable at temperatures as high as 2,500 F (1,400 C), according to the researchers.

In this latest feat, the researchers in Illinois coated commonly used tungsten emitters in a nanolayer of a ceramic hafnium dioxide material.

When subjected to temperatures of 1,800 F (1,000 C), the ceramic-coated emitters retained their structural integrity for more than 12 hours. When heated to 2,500 F (1,400 C), the samples remained thermally stable for at least an hour.

At Stanford, Fan and his colleagues confirmed the ceramic-coated emitters were still capable of producing infrared light waves that are ideal for running solar cells.

“We demonstrated for the first time that ceramics could help advance thermophotovoltaics as well other areas of research, including energy harvesting from waste heat, high-temperature catalysis and electrochemical energy storage,” according to former Illinois graduate student Kevin Arpin, lead author of the study.

“Hafnium and tungsten are abundant, low-cost materials, and the process used to make these heat-resistant emitters is well established. Hopefully these results will motivate the thermophotovoltaics community to take another look at ceramics and other classes of materials that haven’t been considered," said Paul Braun, co-author of the study and a professor of materials science at the University of Illinois-Urbana Champaign.

The researchers plan to test other ceramic-type materials and determine if the experimental thermal emitters can deliver infrared light to a working solar cell.

The results of the study are published in the October 16 edition of the journal Nature Communications.

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