Commercially available triple-junction solar cells utilize a Ge bottom cell with an (In)GaAs and InGaP middle and top cell, respectively. This architecture has a well-known efficiency limitation of ~40% at 500 suns. Higher efficiencies can be achieved by changing the effective bandgaps of the junctions, but the selection of materials and approaches to do so is very limited. Solar Junction has adopted the dilute nitride material system to obtain these new bandgaps and break through the 40% efficiency barrier. The unique and powerful advantage of dilute nitrides is that the bandgap can be tuned and varied while maintaining lattice-matched conditions to Ge or GaAs. The dilute nitride technology in Solar Junction’s first commercial product has enabled a significant improvement in efficiencies by using the optimal set of bandgaps. Commercial Solar Junction concentrator cells with efficiencies of 43.5% have been independently verified by NREL and Fraunhofer. These higher efficiencies are generally the result of higher output voltage, not higher current, which keep system-level resistive wiring losses in check.
© 2011 Optical Society of AmericaPDF Article