We discuss lattice-mismatched (LMM) approaches utilizing compositionally step-graded layers and buffer layers that yield Ill-V photovoltaic devices with performance parameters equaling those of similar latticematched (LM) devices. Our progress in developing highperformance. LMM, InP-based GalnAshAsP materials and devices for thermophotovoltaic (TPV) energy conversion is highlighted. A novel, monolithic. multibandgap, tandem device for solar PV (SPV) conversion involving LMM materials .is also presented along with promising preliminary performance results.
To illustrate the variety and complexity of thermophotovoltaic (TPV) system designs, the present status of selected systems, ranging in power output from 50 W to 2 kW, is reviewed. The design and analysis of each of these power systems is complex due to the interactions among the radiator, photonic cavity and filter/semiconductor device elements. To draw meaningful conclusions and aid the development of new power systems, a methodology for measuring and predicting the performance of system designs is required. To first order, this includes an understanding of the semiconductor diode characteristics, emitter/filter spectra and radiative properties of the system components.
Advanced thermophotovoltaic (TPV) modules capable of producing > 0.3 W/cm 2 at an efficiency > 22% while operating at a converter radiator and module temperature of 1228 K and 325 K, respectively, have been made. These advanced TPV modules are projected to produce > 0.9 W/cm 2 at an efficiency > 24% while operating at a converter radiator and module temperature of 1373 K and 325 K, respectively. Radioisotope and nuclear (fission) powered space systems utilizing these advanced TPV modules have been evaluated. For a 100 W e radioisotope TPV system, systems utilizing as low as 2 general purpose heat source (GPHS) units are feasible, where the specific power for the 2 and 3 GPHS unit systems operating in a 200 K environment is as large as ~ 16 W e /kg and ~ 14 W e /kg, respectively. For a 100 kW e nuclear powered (as was entertained for the thermoelectric SP-100 program) TPV system, the minimum system radiator area and mass is ~ 640 m 2 and ~ 1150 kg, respectively, for a converter radiator, system radiator and environment temperature of 1373 K, 435 K and 200 K, respectively. Also, for a converter radiator temperature of 1373 K, the converter volume and mass remains less than 0.36 m 3 and 640 kg, respectively. Thus, the minimum system radiator + converter (reactor and shield not included) specific mass is ~ 16 kg/kW e for a converter radiator, system radiator and environment temperature of 1373 K, 425 K and 200 K, respectively. Under this operating condition, the reactor thermal rating is ~ 1110 kW t . Due to the large radiator area, the added complexity and mission risk needs to be weighed against reducing the reactor thermal rating to determine the feasibility of using TPV for space nuclear (fission) power systems.
Abstract-A CW laser power of 140 mW was obtained in the 840.39 nm transition of Ag II by electron beam excitation. This electron beam excited metal vapor ion laser is capable of operating using metals with high vaporization temperatures and is of interest for generation of CW coherent radiation in the 220-260 nm spectral region. PREVIOUSLY we reported laser action in ionic and atomic transitions excited by charge transfer reactions [1] and three-body electron-ion recombination [2] in electron beam generated plasmas. CW laser action was obtained in more than 50 infrared and visible lines using de electron beam excitation. In all cases, the active medium was a mixture of helium with another gas or a metal vapor with a relatively low melting point ( < 900 K). In the case of the blue lines of Zn II, an order of magnitude increase in the laser output power and efficiency was obtained with respect to previously used hollow cathode discharges [1]. The electron beam charge transfer excitation scheme also has the potential of producing CW laser light with higher output powers than presently obtainable in the 220-260 nm spectral region. In this case, the active medium must contain Ag, Cu, or Au vapor [3]- [6]. The required metal vapor concentrations are on the order of 10 15 atoms · em -3 , and the associated vaporization temperatures are between 1400 and 2100 K. The optimum metal vapor concentration depends on the plasma density, temperature, and radius. This optimum vapor concentration is the minimum metal atom density required to make charge transfer the dominant loss channel for the noble gas ions over diffusion to the walls and electron-ion recombination.Molecular donors have been used to produce concentrations of these atoms [7], [8], but their use is unsuitable in ultraviolet lasers because of the unacceptable high losses caused by absorption of the laser radiation by molecular transitions. Here we discuss an electron beam laser capable of operating with metal vapors requiring a high vaporization temperature, and we report its CW operation in the 840.39 nm (6p
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