Department of Energy grant aims for more efficient solar technology

PULLMAN, Wash. – A team of Washington State University and National Renewable Energy Laboratory researchers has received a U.S. Department of Energy award to advance solar energy research and development.

Led by John McCloy, professor in the School of Mechanical and Materials Engineering and director of the Institute of Materials Research, the team aims to improve cadmium telluride (CdTe) solar technology to make it more competitive with silicon solar cells, which currently makes up 90 percent of the solar cell market.

“This project aims to combine the low-cost manufacturing advantage of cadmium telluride technology with strategies to increase efficiency and reliability,” McCloy said. “I believe this project’s success will positively impact the US solar industry, manufacturing, and energy security, since the US is the leading manufacturer of CdTe photovoltaics.”

Because of the way that they’re manufactured, CdTe solar cells offer a low‑cost alternative to silicon. They have the lowest carbon footprint and perform better than silicon in real world conditions, including in hot, humid weather and under low light. While they can be manufactured easily, however, they underperform in the maximum voltage available from the solar cell, called open-circuit voltage. Researchers have been working to improve the efficiency of the technology but have been unable to reach its predicted limits.

A few years ago, a team of researchers from WSU, NREL, and the University of Tennessee, made a key improvement in the technology by adding phosphorus doping atoms during the manufacturing process, improving its open‑circuit voltage. WSU researchers also used similar doping techniques to add indium to cadmium selenium telluride (Cd-Se-Te) and CdTe crystals to change the electrical conductivity mode to conduct electrons, rather than the hole carriers that are typically used in phosphorus-containing materials.

“WSU and NREL have a longstanding history of developing novel doping to advance photovoltaics,” said McCloy.

As part of the new $300,000 award from the Solar Energy Technologies Office (SETO), the researchers are using electron-doped and hole-doped CdTe together to improve an interface between these semiconductor materials.  SETO supports early-stage research and development to improve the affordability, reliability, and domestic benefit of solar technologies on the grid.

The researchers hope that their work will lead to increased efficiency to enable the CdTe technology to reach an energy cost target of 2 cents per kilowatt hour, which is the cost needed to make solar electricity cost-competitive with traditionally generated electricity.

“CdTe is the leading thin-film photovoltaic technology with the lowest cost per watt due to its low-cost manufacturing,” McCloy said. “The cost can be further reduced by improving efficiency without significantly changing manufacturing processes.”

The WSU team was selected as a part of the SETO Fiscal Year 2020 funding program, an effort to advance research and development projects that will lower solar electricity costs, increase the competitiveness of American solar manufacturing and businesses, improve the reliability and resilience of the grid, and expand solar to new applications. They are one of several photovoltaic (PV) projects that will improve PV device efficiency, service lifetime, and manufacturability of PV technologies.

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