This paper presents an analysis of the photovoltaic characteristics and parameters of individual subcells of space multi-junction solar cells after irradiation by high-energy particles. Dark currents, charge carrier lifetimes, and damage coefficients for wide-bandgap subcells were determined both theoretically and experimentally.

This work is devoted to the study of the effect of temperature on the spectral irradiance blurring (concentrated in the focal plane of a Fresnel lens) arising due to the inher-ent chromatic aberration (CA) of the lens. This paper presents equipment for recording both irradiance distribution and spectral irradiance redistribution for the radiation concentrated by a small-sized energy concentrator adapted to temperature measurements, as well as the results of a study of Fresnel lenses.

Based on the electroluminescent method and the two-diode equivalent circuit model of a solar cell, the current-voltage characteristics of wide-bandgap subcells in the struc-ture with the corresponding parameters of saturation dark currents are obtained. In addition, the approach has been tested on samples exposed to various radiation doses, which made it possible to determine the degradation rate of the photovoltaic characteristics of solar cells.

Temperature dependencies of the refractive indices, n, for InxGa1-xAs and InxAl1-xAs metamorphic layers with x=0.06-0.25 have been determined. For this purpose, we performed variable-temperature (80 to 400 K) measurements of the specular reflection coefficient using custom distributed-Bragg-reflector structures in the spectral range from 0.8 µm to 2.2 µm. All the compositions exhibited a nearly linear temperature dependence of n. For InxGa1-xAs, the temperature coefficient (dn/dT) increases from 2.0⋅10-4K-1 for x=0.06 to 4.5⋅10-4K-1 at x=0.25. In turn, the temperature coefficient of the InxAl1-xAs refractive index stays at the level of (1.7-2.0)⋅10-4K-1 at the considered indium contents.

The influence exerted by the carrier concentration in the range (1–50) × 1014 cm–3 in n-4H-SiC chemical-vapor deposited (CVD) epitaxial layers on the spectral characteristics of UV photodetectors with Cr Schottky barriers in the range of 200–400 nm is revealed and explained in terms of the photoconductivity theory. Schottky barriers with a Cr film thickness of 20 nm and diameter of 8 mm are formed by thermal evaporation in vacuum through masks. A noticeable effect of the carrier concentration in the CVD epitaxial layers on the spectral characteristics of photodetectors upon heating to 200°C is also observed and accounted for by a difference between the generation-recombination processes. The irradiation of photodetectors with 15-MeV protons at a fluence of 4 × 1012 cm–2 and a temperature of 200°C leads to an increase in the quantum efficiency as compared to samples irradiated in similar modes at 25°C. This is indicative of an increase in the radiation hardness and service life of 4H-SiC devices at elevated temperatures.

The effect of irradiation by protons with an energy of 15 MeV with fluences of (1-40)٠1012 cm-2 on the spectral characteristics of UV 4H-SiC photodetectors was considered. Photodiodes with Schottky barriers were formed by thermal vacuum sputtering with a thickness of 20 nm and a diameter of 8 mm on 4H-SiC structures with CVD epitaxial layers with a concentration of uncompensated donors Nd-Na=(1-4)٠1014 cm-3 grown on n+-4H-SiC substrates. UV photodetectors withstand irradiation by protons with a fluences of 4٠1013 cm-2 with a photosensitivity improvement due to the gettering of simple radiation defects by localized cluster and amorphous areas, and partial structural improvement of the irradiated material. Irradiation of photodetectors by 15 MeV protons with a fluence of 4٠1012 cm-2 at a temperature of 2000 C led to an increase in quantum efficiency compared to samples irradiated in similar modes at 250 C due to an additional defective rearrangement.

The paper proposes an experimental approach to determine the external quantum efficiency of multijunction solar cells with pronounced optical coupling. A new technique based on the cascade mechanism of coupling has been elaborated to separate the influence of the induced luminescent flux from the external illumination and to establish the absolute values of photosensitivity without negative impact of optical interaction between subcells. The novelty of this work lies in the method extended to multijunction devices with N-number of subcells.

Abstract The influence exerted by the carrier concentration in the range (1–50) × 10^14 cm^–3 in n -4 H -SiC chemical-vapor deposited (CVD) epitaxial layers on the spectral characteristics of UV photodetectors with Cr Schottky barriers in the range of 200–400 nm is revealed and explained in terms of the photoconductivity theory. Schottky barriers with a Cr film thickness of 20 nm and diameter of 8 mm are formed by thermal evaporation in vacuum through masks. A noticeable effect of the carrier concentration in the CVD epitaxial layers on the spectral characteristics of photodetectors upon heating to 200°C is also observed and accounted for by a difference between the generation-recombination processes. The irradiation of photodetectors with 15-MeV protons at a fluence of 4 × 10^12 cm^–2 and a temperature of 200°C leads to an increase in the quantum efficiency as compared to samples irradiated in similar modes at 25°C. This is indicative of an increase in the radiation hardness and service life of 4 H -SiC devices at elevated temperatures.

Abstract In the present work processes of direct light coupling in the triple-junction solar cells between top GaInP (wide band gap) and bottom Ge (narrow band gap) subcells are considered, when parameters of intermediate optical medium (comprised of middle GaAs p-n junction layers) are changed. Conditions of luminescent coupling gain and blocking are studied in multijunction structures with selectively tuned built-in photonic structures such as Bragg reflectors. An ability to manage the efficiency of optical interaction between subcells is investigated.

A quantitative error analysis in determining minority charge carrier lifetimes in photoactive layers of III-V photovoltaic cells (multijunction solar and laser power converters) has been carried out. Accuracies of the methods based on simulation: of the spectral dependencies of the internal quantum yield, of photovoltaic cells' dark current densities and transient characteristics in dependence on peculiarities of the heterostructure and of the measurement range have been compared. It has been found that error diagrams for any material can be represented in normalized form with respect to absorption coordinates. Using this assumption estimated were diffusion length relative error values for the base and emitter layers.

The work is aimed at the study of multijunction solar cells with built-in Bragg reflectors. The possibility to use the photon structure for “locking” the secondary recombination radiation, which causes luminescent coupling between individual photoactive p-n junctions in a solar cell, is investigated. Temperature studies were carried out on the reflection spectra of a Bragg reflector, the electroluminescence spectrum of a middle wide bandgap subcell, and the spectra of the external quantum efficiency of a multijunction solar cell.

In this paper, triple-junction solar cells of various middle junction thickness are studied. It is shown that in samples with thin layers, an optical coupling between the top and the bottom subcell is possible as well as a direct leakage of external radiation through the middle one. True values of the spectral dependences of the external quantum efficiency are calculated in accordance with the corrective method. The proposed method reveals some difference in the negative contribution of the luminescence and the positive signal results from the light penetration.

In the present work processes of light redistribution within the multijunction solar cell were investigated. The possibility to control efficiency of luminescent coupling, up to its totally blocking, is described. Temperature of the tested sample is used to provide optical coupling management. Direct penetration of recombination photons from top to bottom p-n junction was observed. The dependence of top-bottom coupling efficiency was studied depending on the thickness of middle subcell layers.

Solar spectral irradiance blurring in the focal plane of the Fresnel lens arising from the chromatic aberration (CA) inherent to a lens was studied. The experimental complex for recording both irradiance distribution and spectral irradiance redistribution for the radiation concentrated by a small-sized energy concentrator based on a solar simulator with the possibility of modeling the spectral composition of light is presented. The methodology for scanning the irradiance spectral redistribution by a fiber spectrometer is described.

In the work, a new experimental equipment to investigate optical and power characteristics of small-size sunlight concentrators (Fresnel lenses) is presented. The system is based on a continuous sunlight simulator with a specular optics. The scheme and design parameters to register spatial distribution of illumination formed by the sunlight concentrator are determined. The compromise solution in the simulation of sunlight parameters was chosen to achieve the goals of the study. The optical system forming collimate light flux fully satisfies the requirements for illumination, spectral composition and angular divergence. The pair "spectrum-angular divergence" was defined as the relevant to determine concentrating capability and optical-power efficiency of Fresnel lenses. A monitoring technique for parameters of the initial light flux and a registration procedure for the irradiance distribution profile in the Fresnel lens focal plane were developed.

In the present research, a multijunction solar cell with a built-in 1D photonic structure − Bragg reflector − is investigated. The joint effect of photon recycling and luminescence coupling on the spectral characteristics of the external quantum efficiency of multijunction solar cells is considered.

Presented are technical solutions on constructing optical systems for experimental simulating the sunlight parameters. Designs of two types of solar simulators are proposed. In the first one, the spectrum and the radiation angular divergence are simulated on the basis of a continuous light source, what corresponds to the principle “necessity and sufficiency” of simulated parameters of the light flux in investigating optical and power characteristics of small-size sunlight concentrators (Fresnel lenses). In the second type simulator, based on a pulsed radiation source, the emphasis has been placed on high-quality simulation of irradiance and spectrum for satisfying requirements in recording current-voltage characteristics of multijunction solar cells and in determining their efficiency.

In the present work, an opportunity to block the negative influence of luminescent coupling between subcells in multijunction solar cells with help of built-in Bragg reflectors is investigated. Temperature modes, at which the blocking of optical interaction in the GaAs-Ge pair of subcells is possible, have been determined.

In the work, optical coupling arising in a multijunction solar cell under powerful laser radiation is investigated. To describe the cascade of interconnected luminescent processes in a structure with optical coupling, the photon-coupled characteristic is used. Investigation for two specimens with different effeciency of luminescent interaction was carried out.

In this work, a new approach to find absolute values of the external quantum efficiency of multijunction solar cells with strong optical coupling between individual subcells is proposed. A distinctive feature of the approach is a single wavelength light biasing - blue laser - for providing required conditions for recording the narrowband subcell spectral characteristics. To find the true photoresponse values (without the negative influence of the optical coupling) a two-dimensional current plane describing photocurrents of subcells and their impact on each other is performed.