The U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) says it and partners have reached a critical milestone in cadmium telluride (CdTe) solar cell technology, helping pave the way for solar energy to directly compete with electricity generated by conventional energy sources.
Scientists at NREL collaborated with researchers at Washington State University and the University of Tennessee to improve the maximum voltage available from a CdTe solar cell, which NREL says is a key factor in improving solar cell efficiency. The research appears in the Nature Energy journal article “CdTe solar cells with open-circuit voltage breaking the 1 V barrier.”
According to NREL, silicon solar cells currently represent 90% of the solar cell market, but it will be difficult to significantly reduce their manufacturing costs. The lab says CdTe solar cells offer a low-cost alternative, have the lowest carbon footprint and adapt better than silicon in real-world conditions, including hot, humid weather and low light. However, NREL adds, CdTe solar cells have not been as efficient as multicrystalline silicon solar cells until recently.
One key area where CdTe has underperformed is in the maximum voltage available from the solar cell, a measure called open-circuit voltage, the lab explains. The quality of CdTe materials has prevented industry, universities and national laboratories for the past 60 years from obtaining open-circuit voltage exceeding 900 millivolts on billions of solar cells; NREL says the vast majority have been limited to 750 to 850 millivolts.
The research team improved cell voltage by shifting away from a standard processing step using cadmium chloride. Instead, the researchers placed a small number of phosphorus atoms on tellurium lattice sites and then carefully formed ideal interfaces between materials with different atomic spacing to complete the solar cell. NREL says this approach improved the CdTe conductivity and carrier lifetime each by orders of magnitude, thereby enabling the fabrication of CdTe solar cells with an open-circuit voltage breaking the 1-volt barrier for the first time.
The lab says this innovation establishes new research paths for solar cells to become more efficient and provide electricity at lower cost.
The research was funded by the Energy Department’s SunShot Initiative, which aims to make solar cost-competitive with traditional energy sources. It was also supported, in part, by Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences.