Single junction InGaP/GaAs solar cells displaying high efficiency and record high open‐circuit voltage values have been grown by metal–organic chemical vapor deposition on Ge/graded SiGe/Si substrates. Open‐circuit voltages of 980 mV under AM0 conditions have been verified to result from a single GaAs junction, with no evidence of Ge‐related sub‐cell photoresponse. AM0 efficiencies close to 16% have been measured for a large number of small‐area cells, the performance of which is limited by non‐fundamental current losses due to significant surface reflection resulting from> 10% front‐surface metal coverage and wafer handling during the growth sequence for these prototype cells. It is shown that at the material quality currently achieved for GaAs grown on Ge/SiGe/Si substrates, namely a 10 ns minority‐carrier lifetime that results from complete elimination of anti‐phase domains, and maintaining a threading dislocation density of ∼8 × 105 cm−2, 19–20% AM0 single‐junction GaAs cells are imminent. Experiments show that the high performance is not degraded for larger‐area cells, with identical open‐circuit voltages and higher short‐circuit current (due to reduced front metal coverage) values being demonstrated, indicating that large‐area scaling is possible in the near term. Comparison with a simple model indicates that the voltage output of these GaAs‐on‐Si cells follows the ideal behavior expected for lattice‐mismatched devices, demonstrating that unaccounted‐for defects and issues that have plagued other methods to epitaxially integrate III–V cells with Si are resolved by using SiGe buffers and proper GaAs nucleation methods. These early results already show the enormous and realistic potential of the virtual SiGe substrate approach for generating high‐efficiency, lightweight and strong III–V solar cells. Copyright © 2002 John Wiley & Sons, Ltd.
Autonomous systems are increasingly used to provide situational awareness and long-term environment monitoring. Photovoltaics (PV) are favored as a long-endurance power source for many of these applications. To date, the use of PV is limited to space and terrestrial (dry-land) installations. The need for a persistent power source also exists for underwater (UW) systems, which currently rely on surface PV arrays or batteries. In this paper, we demonstrate that high-bandgap-InGaP solar cells can provide useful power UW.
Abstract. The Materials Adherence Experiment (MAE) on Pathfinder was designed to measure the rate of dust settling from the Martian atmosphere onto the solar array of the Mars Pathfinder Sojourner Rover. The MAE measurements indicate steady dust accumulation at a rate of about 0.28% per day. This value is consistent with the performance of the lander solar arrays, which decreased in power at an estimated rate of 0.29% per day over the same period. IntroductionThe atmosphere of Mars contains suspended dust, which creates the characteristic light color of the sky seen in photographs taken from the surface of Mars. The amount of atmospheric dust varies, increasing when local or global dust storms raise dust into the atmosphere, decreasing in clear conditions, but the atmosphere is rarely or never completely free of dust.Dust raised by storms will eventually settle out of the atmosphere. The rate and mechanism of atmospheric dust settling are not well characterized, but they are expected to be both geographically variable and to vary from season to season and from year to year.To determine whether atmospheric dust settling will be a problem for longer-duration solar-powered probes to Mars, the "Materials Adherence Experiment" (MAE) was designed to quantify the effect of dust deposition from the Martian atmosphere on the performance of the solar array [Landis and Flood, 1992; Landis, 1993; Jenkins et al., 1997]. The purpose of this instrument was to make a measurement by which degradation of the array output due to dust coverage could be reliably separated from degradation due to other causes or changes in output due to variations in the solar intensity at the surface. With this instrument we have made the first quantitative measurement of the amount of dust deposited and the effect of settled dust on solar cell performance. MAE InstrumentThe MAE experiment is mounted on the front left corner of the solar array of the "Sojourner" rover, as shown in Figure 1 Measurementswere made at noon and at 1400 local solar time. Unfortunately, the tilt of the rover relative to the Sun is dependent on the local terrain, and therefore the measurement has slight variations due to nonnormal angle of incidence. For measurements taken at solar noon, the angle of incidence is typically within reasonable tolerances, but there is considerably more scatter in measurements taken later in the day. The experiment requires that the rotating arm fully remove the cover glass from in front of the solar cell. The rover energizes the actuator, waits a predetermined time, and then measures the solar cell. The measurement is then repeated after the cover is closed. The cover glass reflects 6% of the incident light. Therefore a verification of whether the cover glass has been removed is obtained by measuring at least a 6% increase in lsc when the cell is uncovered.Since the SMA action is thermal in nature, ambient temperature plays an important role in determining how much current is required to activate the rotating arm. Shortly after landing, we pe...
Radiation tolerance is a critical performance criterion of photovoltaic devices for space power applications. In this paper we demonstrate the intrinsic radiation tolerance of an ultra-thin solar cell geometry. Device characteristics of GaAs solar cells with absorber layer thicknesses 80 nm and 800 nm were compared before and after 3 MeV proton irradiation. Both cells showed a similar degradation in Voc with increasing fluence; however, the 80 nm cell showed no degradation in Isc for fluences up to 1014 p+ cm−2. For the same exposure, the Isc of the 800 nm cell had severely degraded leaving a remaining factor of 0.26.
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