Scientists at the Energy Department’s National Renewable Energy Laboratory (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 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,” authored by James Burst, Joel Duenow, David Albin, Eric Colegrove, Matthew Reese, Jeffery Aguiar, Chun-Sheng Jiang, Maulik Patel, Mowafak Al-Jassim, Darius Kuciauskas, Santosh Swain, Tursunjun Ablekim, Kelvin Lynn, and Wyatt Metzger.
Silicon solar cells currently represent 90% of the solar cell market, but it will be difficult to significantly reduce their manufacturing costs. CdTe solar cells offer a low-cost alternative. These cells also have the lowest carbon footprint and adapt better than silicon in real-world conditions including hot, humid weather and low light. However, 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 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; the vast majority has 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, 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.