Production data on 0.55 eV InGaAs thermophotovoltaic cells

Low bandgap 0.55 eV (2.25 {micro}m cutoff wavelength) indium gallium arsenide (In{sub 0.72}Ga{sub 0.28}As) thermophotovoltaic (TPV) cells use much more of the long wavelength energy emitted from low temperature (< 1,200 C) thermal sources than either Si or GaSb cells. Data are presented on a statistically significant number (2,500) of these TPV cells, indicating the performance obtainable in large numbers of cells. This data should be useful in the design and modeling of TPV system performance. At 1.2 A/cm{sup 2} short-circuit current, an average open-circuit voltage of 283 mV is obtained with a 60% fill factor. The peak external quantum efficiency for uncoated cells is 65% and is over 50% from 1.1 to 2.2 {micro}m. Internal quantum efficiency is over 76% in this range assuming an estimated 34% reflectance loss

MBE growth of GaInAsSb p/n junction diodes for thermophotovoltaic applications

This paper reports recent progress in the development of quaternary III-V thermophotovoltaic (TPV) devices based on MBE grown Ga{sub x}In{sub 1{minus}x}As{sub y}Sb{sub 1{minus}y}. TPV is of great interest for a variety of applications. The objective of this work is to develop a TPV cell which is tunable to the emission spectrum of a heated blackbody, at temperatures in the range of 1200--1473 K. One aspect of this tuning is to match the band gap, E{sub gap}, of the photovoltaic device to the peak output of the heat source., An advantage of the quarternary III-V semiconductor systems is that devices can be fabricated by molecular beam epitaxy on a suitable binary substrate, such as GaSb or InAs, and the band gap and lattice constant can be adjusted more or less independently, to match requirements. Quarternary cells, with band-gaps in the 0.5 to 0.72 eV range, have been fabricated and tested. For 0.54 eV devices the authors obtained V{sub oc} = 0.3 V and I{sub sc} = 1.5 amperes/cm{sup 2} under infrared illumination of a 1200 K blackbody. Under high illumination levels the V{sub oc} and I{sub sc} ranged from 0.5 V at 3 amperes/cm{sup 2} for 0.72 eV devices to 0.31 V at 1.2 amperes/cm{sup 2} for 0.5 eV devices, indicating good photovoltaic device characteristics over the range of bandgaps. The diode ideality factor for 0.54 eV devices ranged from 2.45 at low illumination indicating tunneling-dominated dark current, to 1.7 at high illumination intensity indicating recombination-generation dominated dark currents

Limiting phase separation in epitaxial GaInAsSb

GaInAsSb alloys are of great interest for lattice-matched thermophotovoltaic (TPV) devices because of the high performance attainable at 2.2 {micro}m. Extension of the TPV device cutoff wavelength to beyond 2.2 {micro}m is especially desirable since the emissive power of the source is significant at these longer wavelengths. However, the GaInAsSb quaternary alloy system exhibits a miscibility gap in the wavelength range of interest, and no devices with cutoff wavelengths longer than 2.3 {micro}m have been demonstrated. This paper reports the successful growth of GaInAsSb alloys which exhibit room temperature photoluminescence (PL) at wavelengths as long as 2.5 {micro}m. TPV devices with cutoff wavelengths out to 2.5 {micro}m exhibit external quantum efficiencies of 57%. These values are comparable to those measured for 2.2 {micro}m devices

Current status of low-temperature radiator thermophotovoltaic devices

The current performance status of low-temperature radiator (< 1,000 C) thermophotovoltaic (TPV) devices is presented. For low-temperature radiators, both power density and efficiency are equally important in designing an effective TPV system. Comparisons of 1 cm x 1 cm, 0.55 eV InGaAs and InGaAsSb voltaic devices are presented. Currently, InGaAs lattice-mismatched devices offer superior performance in comparison to InGaAsSb lattice-matched devices, due to the former`s long-term development for numerous optoelectronic applications. However, lattice-matched antimony-based quaternaries offer numerous potential advantages

Measurements of Conversion Efficiency for a Flat Plate Thermophotovoltaic System Using a Photonic Cavity Test System

The performance of a 1 cm{sup 2} thermophotovoltaic (TPV) module was recently measured in a photonic cavity test system. A conversion efficiency of 11.7% was measured at a radiator temperature of 1076 C and a module temperature of 29.9 C. This experiment achieved the highest direct measurement of efficiency for an integrated TPV system. Efficiency was calculated from the ratio of the peak (load matched) electrical power output and the heat absorption rate. Measurements of these two parameters were made simultaneously to assure the validity of the measured efficiency value. This test was conducted in a photonic cavity which mimicked a typical flat-plate TPV system. The radiator was a large, flat graphite surface. The module was affixed to the top of a copper pedestal for heat absorption measurements. The heat absorption rate was proportional to the axial temperature gradient in the pedestal under steady-state conditions. The test was run in a vacuum to eliminate conductive and convective heat transfer mechanisms. The photonic cavity provides the optimal test environment for TPV efficiency measurements because it incorporates all important physical phenomena found in an integrated TPV system: high radiator emissivity and blackbody spectral shape, photon recycling, Lambertian distribution of incident radiation and complex geometric effects. Furthermore, the large aspect ratio between radiating surface area and radiator/module spacing produces a view factor approaching unity with minimal photon leakage

Higher Rates of Hemolysis Are Not Associated with Albuminuria in Jamaicans with Sickle Cell Disease

BACKGROUND: Albuminuria is a marker of glomerular damage in Sickle Cell Disease (SCD). In this study, we sought to determine the possible predictors of albuminuria in the two more prevalent genotypes of SCD among the Jamaica Sickle Cell Cohort Study participants. METHODS: An age-matched cohort of 122 patients with HbSS or HbSC genotypes had measurements of their morning urine albumin concentration, blood pressure, body mass index, haematology and certain biochemistry parameters done. Associations of albuminuria with possible predictors including hematological parameters, reticulocyte counts, aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) levels were examined using multiple regression models. RESULTS: A total of 122 participants were recruited (mean age 28.6 years ±2.5 years; 85 HbSS, 37 HbSC). 25.9% with HbSS and 10.8% with HbSC disease had microalbuminuria (urine albumin/creatinine ratio  =  30-300 mg/g of creatinine) whereas 16.5% of HbSS and 2.7% of HbSC disease had macroalbuminuria (urine albumin/creatinine ratio>300 mg/g of creatinine). Mean arterial pressure, hemoglobin levels, serum creatinine, reticulocyte counts and white blood cell counts were statistically significant predictors of albuminuria in HbSS, whereas white blood cell counts and serum creatinine predicted albuminuria in HbSC disease. Both markers of chronic hemolysis, i.e. AST and LDH levels, showed no associations with albuminuria in either genotype. CONCLUSIONS: Renal disease, as evidenced by excretion of increased amounts of albumin in urine due to a glomerulopathy, is a common end-organ complication in SCD. It is shown to be more severe in those with HbSS disease than in HbSC disease. Rising blood pressure, lower hemoglobin levels and higher white blood cell counts are hints to the clinician of impending renal disease, whereas higher rates of hemolysis do not appear to play a role in this complication of SCD