The most common triple-junction solar cell design which has been commercially available to date utilizes a germanium bottom cell with an (In)GaAs and InGaP middle and top cell respectively. This type of device has a well-known efficiency limitation somewhere around 40% at 500 suns. Higher efficiencies can be obtained by changing the effective bandgaps of the three junctions, but the choice of materials and approaches to do so is very limited. We at Solar Junction have adopted the dilute nitride material system to obtain these new bandgaps, and break through the 40% efficiency barrier. The unique advantage of the dilute nitrides is that the bandgap and lattice constant can be tuned independently, allowing bulk material lattice matched to Germanium or GaAs over a wide range of bandgaps. The dilute nitride technology in our first commercial product has enabled us to maximize the efficiency of a triple junction solar cell by using the optimal set of bandgaps (including one around 1eV). 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 keeps system-level resistive wiring losses in check.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.