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A high-altitude AM0 solar cell calibration platform capable of attaining conditions close to those of space, i.e. 30km (100,000ft) or more is presented. The platform leverages the latest advances in the fields of miniaturized flight control electronics and sun pointing systems. This provides the ability to build a calibration platform of comparable or superior performance to previous airplane and balloon based systems but at two to three orders of magnitude less weight and size which results in launches with lower operating cost and short notice. Further advantages are the capability to measure temperature coefficients and a guided retrieval system. Test and high-altitude flight data are presented.

The transport processes of majority carriers through potential barriers at heterointerface layers of GaAs solar cell structures are experimentally analyzed by optical-injection-dependent and temperature-dependent current–density voltage (J–V) measurements. It is shown that the influence of front-surface-field and back-surface-field layers on majority carrier transport mechanisms is most pronounced in the J--V characteristics when high-concentration or low-temperature operating conditions are concerned. A method to determine the effective majority carrier potential barrier height at heterointerfaces is described and exemplified at GaAs solar cells structures. Discussion is provided on how a significant improvement of the majority carrier flow at heterointerfaces is achievable by modification of the doping concentration profiles of the solar cell structure. The results are also applicable to other optoelectronic devices such as light-emitting diodes or detectors.

This contribution discusses the radiation hardness of germanium (Ge) photovoltaic cells under space conditions corresponding to an irradiation dose of 1-MeV 1 × 1015 cm-2 electrons. For this purpose, different germanium photovoltaic cell technologies based on p-type substrates are analyzed. The investigation comprises standard Ge photovoltaic cells with a substrate doping concentration of NA = 1 × 1017 cm-3, as well as recently developed Ge photovoltaic devices with extended quantum efficiency in the IR (λ > nm), which are based on low-doped substrates with NA = 1-4 × 1016 cm-3 in conjunction with an electrical rear-side passivation layer. In comparison to the standard Ge photovoltaic cell design, higher germanium subcell current densities of up to 14% at begin of life and up to 13% after electron exposure are achieved. This is particularly advantageous for high-efficiency metamorphic GaInP/GaInAs/Ge triple-junction solar cell structures, where the Ge subcell may become current limiting. Measurement results are presented, showing that the quantum efficiency related to the direct and indirect absorption transitions is differently affected by the cosmic electron particle irradiation. Furthermore, the impact of irradiation on free carrier absorption processes is discussed.

In this paper we present a methodology that uses the detailed balance method to determine the optimum bandgap combination of III–V triple-junction solar cells for the highest yearly energy production. As an example of the methodology, we analyze two geographical locations on Earth with distinct spectral conditions. For these places the monthly average of the measured aerosol optical depth and the precipitable water are used to calculate direct solar spectra with a discretisation of one spectrum per hour. The model is used to analyze the spectral sensitivity of the bandgap design of four practical III–V triple-junction solar cell structures. Furthermore, the ideal bandgap combination for a maximal energy harvest is calculated for each location. It is shown that the metamorphic solar cell structure of Ga0.35In0.65P/Ga0.83In0.17As/Ge with transparencies optimized for the standard AM1.5d reference spectrum leads to the highest energy harvesting efficiencies and shows the lowest spectral sensitivity. The standard lattice-matched structure of Ga0.50In0.50P/Ga0.99In0.01As/Ge shows the highest spectral sensitivity with up to 10%rel difference in the yearly energy harvesting.

Based on theoretical considerations, optimum triple-junction bandgap combinations are determined in order to achieve highest electrical energy production for a mission on the Martian surface. The solar cell structures analysed in this contribution are based on the Ga y In 1-y P, Ga x In 1-x As and Ge material system. A comparison of theoretical and already realised triple-junction solar cell structures is presented. For the evaluation of long-term electrical energy production, different geographic and climatic Martian scenarios are considered. Copyright © 2010 John Wiley & Sons, Ltd.

In recent years, the implementation of bandgap engineering techniques for solar energy conversion has been demonstrated with exciting results, using both quantum wells (QWs) and quantum dots. Here, the exploitation of a fully lattice-matched QW / barrier system is introduced as an attractive new possibility for this type of device. Photovoltaic characterization is performed and relevant solar cell parameters are reported. For these devices, sixteen layers of 5 nm InGaAs QWs / 10 nm InAlGaAs barriers were embedded into the i-region of a 1.0 eV InAlGaAs solar cell, and the results compared to a 1.0 eV InAlGaAs control solar cell. One-sun J sc is enhanced in the QW cell by 5.3% compared to that of the InAlGaAs control device, while the open circuit voltage is reduced by 153 mV compared to the control. External quantum efficiency measurements reveal a 1.6 mA/cm2 gain from the QW absorption region.

The effect of particle radiation in multi quantum well (MQW) multi-junction InGaP/MQW-InGaAs/Ge solar cells was studied. For comparison purposes, and to identify the origin of the degradation, the same study was performed in the correspondent iso-type cells. Results show that under 1 MeV electron irradiation the MQW-middle junction dictates the degradation of the triple junction cell. Alternative, more radiation hard, designs are presented.

Tailoring bandgaps by introducing quantum wells into the intrinsic region of a solar cell has been shown to improve the energy conversion of these devices. Doping superlattices are a potential way to achieve sub-bandgap absorption in a photovoltaic device without the need to introduce additional materials or strain balancing. In this paper we investigate the inclusion of doping superlattices in between the base and emitter regions of a photodiode. External quantum efficiency measurements of these devices demonstrate increased absorption below the GaAs band edge with respect to a GaAs reference cell. AM0 Illuminated J-V measurements of these devices exhibited variable results with PN configuration resulting in 0.81 V open circuit voltage and 7.7 mA/cm2 short circuit current density. Dark J-V curves show a negative differential resistance region indicating tunneling between the n and p doped regions of the doping superlattice. These results suggest that doping induced superlattices may be an effective way to promote subgap photocurrent in a single junction GaAs cell. Additionally, a subcell in a multi-junction stack could employ this structure utilizing the increased design flexibility as compared to conventional heterojunction quantum well solar cells.

In this paper the temperature-dependent behavior of GaAs single-junction solar cells is studied using both experimental and simulation tools. A cryostat is used to allow measurements of the external quantum efficiency (EQE) and IV curve at different temperatures with the corresponding experimental setup at Fraunhofer ISE. Two different GaAs single-junction solar cell structures are characterized in a wide temperature range between 203 K and 398 K. Through numerical modeling of the GaAs solar cells in a semiconductor simulation environment a deeper understanding of the cells' temperature-dependent behavior is obtained. A good correlation between measurement and simulation results is achieved.

A theoretical analysis on the spectral sensitivity of the bandgap design of four practical III–V triple‐junction solar cell structures is presented. The underlying solar cell model uses the detailed balance method. Six locations on Earth are investigated for which the monthly average of the measured aerosol optical depth and the precipitable water are used to calculate direct solar spectra with a discretisation of one spectrum per hour. The model is used to analyze the solar cell designs for the highest yearly energy production. Furthermore, the ideal bandgap combination for a maximal energy harvest is calculated for each location. It is shown that the metamorphic solar cell structure of Ga0.35In0.65P/Ga0.83In0.17As/Ge with transparencies optimized for the standard AM1.5d reference spectrum leads to the highest energy harvesting efficiencies and shows the lowest spectral sensitivity. The standard lattice‐matched structure of Ga0.50In0.50P/Ga0.99In0.01As/Ge shows the highest spectral sensitivity with up to...

Based on theoretical considerations, optimum triple-junction bandgap combinations are determined to achieve highest electrical energy production for a long-term mission on the Martian surface. The solar cell structures analyzed in this contribution are based on the GaInP/GaInAs/Ge material system. Realistic ambient temperature and atmospheric dust profiles as well as spectral illumination conditions as observed on the Martian surface are considered. The variation of optimum bandgap combinations during the yearly cycle is discussed with respect to the environmental parameters.