Scientists at the National Renewable Energy Laboratory (NREL) have collaborated with researchers at Washington State University and the University of Tennessee to improve the maximum voltage available from a cadmium telluride (CdTe) solar cell—a development they say could help pave the way for solar energy to compete directly with electricity generated by conventional energy sources.

Silicon solar cells currently represent 90% of the solar cell market but, according to NREL, it will likely be difficult to significantly reduce their manufacturing costs. CdTe solar cells offer a lower-cost, lower-carbon-footprint alternative that adapts better than silicon in real-world conditions, including low light and hot, humid weather. However, CdTe solar cells have not been as efficient as multicrystalline silicon solar cells until recently.

CdTe solar cells with open-circuit voltage above 1 volt have been fabricated for the first time. Image credit: Dennis Schroeder/NREL.One key area where CdTe has underperformed in is the maximum voltage available from the solar cell, a measure called open-circuit voltage. Historically, the quality of CdTe materials has prevented industry, universities and national laboratories from obtaining open-circuit voltage exceeding 900 millivolts; the vast majority have been limited to 750 to 850 millivolts.

The research team was able to improve cell voltage by shifting away from a standard processing step that uses cadmium chloride. Instead, they 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.

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 innovation establishes new research paths for solar cells to become more efficient and provide electricity at lower cost.