84 to 1.0 eV. The structures were grown by solid source MBE, equipped with SUMO cells for group III atoms, thermal crackers for group V elements and RF plasma source for atomic N flux generation. The N composition (y) of Ga1−x In x N y As1−y was 0.035 while the In composition (x) was approximately 2.7 times the N composition to ensure lattice matching to GaAs. The GaInNAsSb samples were also closely lattice-matched to GaAs using Sb compositions of up to 0.04. For all structures, the lattice matching was verified by X-ray diffraction measurements. We also fabricated a GaInP/GaAs/GaInNAs triple-junction test SC structure including a GaInNAs subjunction with a bandgap of 0.9 eV. The triple-junction

solar cell and the fabrication details are described elsewhere [10]. After the MBE process, the samples were Bucladesine in vitro processed to solar cells having TiAu contact metals on p-side and NiGeAu for the n-side. Then the surface was coated with a two-layer TiO/SiO antireflection (AR) coating. The current–voltage (I-V) characteristics of single and multijunction solar cells were measured at the real sun (AM1.5G). The real sun intensity level was measured with a Kipp&Zonen check details CM11 pyranometer (Delft, the Netherlands). The external quantum efficiency (EQE) of the GaInNAs SC was also measured. Our EQE system was calibrated using NIST-calibrated Si and

Ge detectors. Moreover, we measured the room-temperature photoluminescence (PL) spectra to determine the bandgaps of GaInNAsSb subjunction materials. The solar cell measurements and calculations OSBPL9 are performed for one sun illumination unless otherwise stated when data is presented. The theoretical efficiency

of the multijunction solar cells incorporating 1 eV GaInNAsSb materials, was estimated using standard diode equations and AM1.5G/D current generation limits set by the absorbed light, bandgap value, and average EQE (EQEav) of each junction. The equations below were used to estimate the I-V characteristics, and were derived from series-connected diodes with two terminals using Kirchhoff’s laws. (1) (2) (3) Here, I is the current of the multijunction device which contains one to four junctions inside, I i is the current through an individual solar cell, V i (I) is the voltage of single-junction device, n i is the quality factor of the ith diode, k B is the Boltzmann coefficient, T is the device temperature (T = 300 K), I Li is the current generated by the junction i, E gi is the bandgap (300 K) of the ith junction, I 0i is the reverse saturation current of the ith junction at 300 K, R s is the device total series resistance, and V is the device total voltage. We have neglected the shunt resistance for simplicity, which is a good approximation for most of the high-quality SC devices. Here, we have also approximated the tunnel junctions as ideal lossless contacts between the solar cell junctions.