S. V. Sorokina

Solar cells based on gallium antimonide

Liquid-phase epitaxy and diffusion from the gas phase have been used to create various kinds of GaSb-based solar cell structures intended for use in cascaded solar-radiation converters. A narrow-gap (GaSb) solar cell was studied in tandem based on a combination of semiconductors GaAs-GaSb (two p-n junctions) and GaInP/GaAs-GaSb (three p-n junctions). The maximum efficiency of photovoltaic conversion in GaSb behind the wide-gap cells is η = 6.5% (at sunlight concentration ratio of 275X, AM1.5D Low AOD spectrum).

Thermophotovoltaic generators based on gallium antimonide

Designs of thermophotovoltaic (TPV) generators with infrared emitters heated by concentrated solar radiation are developed, fabricated, and tested. Emitters made of SiC, W, or Ta of various forms and sizes are studied. To the GaSb-based thermophotovoltaic cells, the efficiency of transformation of thermal radiation of W emitters was 19%. The features of operation of two variants of TPV generators, namely, of cylindrical and conical types, are considered. In a demonstration model of the TPV generator consisting of 12 photocells, the output electric power with conversion of the concentrated solar radiation was P = 3.8 W.

Photovoltaic laser-power converter based on AlGaAs/GaAs heterostructures

Photovoltaic laser-power converters for a wavelength of λ = 809 nm are developed and fabricated on the basis of single-junction AlGaAs/GaAs structures grown by metal-organic vapor-phase epitaxy. The parameters of the photovoltaic structure constituted by an optical “window” and a cladding layer are optimized by mathematical simulation. Photovoltaic converters with areas of S = 10.2 and 12.2 mm2 and 4 cm2 are fabricated and studied. For photocells with S = 10.2 mm2, the monochromatic efficiency (η) was 60% at a current density of 5.9 A/cm2. A photovoltaic module with a working voltage of 4 V (η = 56.3% at 0.34 A/cm2) is assembled.

Simulation of the ohmic loss in photovoltaic laser-power converters for wavelengths of 809 and 1064 nm

The method of mathematical simulation is used to examine the influence exerted by the characteristics of the epitaxial structure and contact grid of photovoltaic laser-power converters on their ohmic loss. The maximum attainable photoconverter efficiency at a Gaussian distribution of the laser-beam intensity on the surface of a photovoltaic converter and at dark-current densities of p–n junctions typical of structures grown by the metal-organic vapor-phase epitaxy (MOVPE) technique are determined. An approach to finding the optimal parameters of GaAs and In0.24Ga0.76As/GaAs photovoltaic converters in relation to the optical power being converted is suggested, and the structural parameters for incident-power values of 5, 20, and 50 W at wavelengths of 809 and 1064 nm are determined. It is found that, at laser-light intensities of up to 5 W, >60% efficiency can be achieved in laser-light conversion at a wavelength of 809 nm and >55% efficiency, at a wavelength of 1064 nm.

A decrease in ohmic losses and an increase in power in GaSb photovoltaic converters

The transmission-line model with radial and rectangular geometry of contact pads has been used to study the contact systems Cr-Au, Cr-Au-Ag-Au, Ti-Pt-Au, Pt-Ti-Pt-Au, Pt-Au, Ti-Au, Ti-Pt-Ag, Ti-Pt-Ag-Au, and Pt-Ag deposited on the p-GaSb surface by the methods of magnetron sputtering and resistive evaporation. It is established that the contact systems Ti-Pt-Ag-Au and Ti-Pt-Ag exhibit the smallest values of the specific contact resistance (ρc ≤ 10−6 Ω cm2), which makes it possible to use these systems in fabrication of photovoltaic converters generating photocurrents with densities as high as 15 A/cm2.

High-efficiency (η = 39.6%, AM 1.5D) cascade of photoconverters in solar splitting systems

A concentrator photovoltaic module with spectral splitting of solar radiation is developed. The module is based on a Fresnel lens and two dichroic filters. Solar cells based on AlGaAs and GaAs are grown by low-temperature liquid-phase epitaxy. GaSb photoconverters are fabricated by zinc gas-phase diffusion into a base epitaxial layer or an n-type GaSb substrate. The total efficiency of three solar cells developed for the spectral splitting module reached 39.6% (AM 1.5D spectrum).

Spectral-splitting concentrator photovoltaic modules based on AlGaAs/GaAs/GaSb and GaInP/InGaAs(P) solar cells

A concentrator photovoltaic module with sunlight spectral splitting by Fresnel lens and dichroic filters is developed. The photoelectric conversion efficiency of such a module is estimated at a level of 49.4% when three single-junction cells are used and may reach 48.5–50.6% when a tandem two-junction cell is combined with narrow-band cells. Single-junction AlGaAs, GaAs, GaSb, and InGa(P)As solar sells are fabricated by zinc diffusion from the vapor phase into an n-type epitaxial layer. GaInP/GaAs cascade solar cells are prepared by MOS hydride epitaxy. The overall efficiency of the three single-junction solar cells developed for the spectral-splitting module is 38.1% (AM1.5D) at concentration ratio Kc = 200x. The combination of the solar cells with the cascade structure demonstrates an efficiency of 37.9% at concentrations of 400–800 suns. The parameters of the spectral-splitting photovoltaic module are measured. The photovoltaic efficiency of this module reaches 24.7% in the case of three single-junction cells and 27.9% when the two-junction and single-junction cells are combined.

High-efficiency GaSb photocells

High-current solar cells based on gallium antimonide and intended for use in solar modules and systems with solar-spectrum splitting at large solar light concentration ratios, in thermophotovoltaic generators with a high-temperature emitter, and in laser energy converters have been designed and fabricated by the diffusion of zinc from the gas phase. The influence exerted by the thickness of the p+ diffusion layer on the basic characteristics of the solar cell has been studied. The optimal doping profile and the p-n-junction depth providing a high photovoltaic conversion efficiency at photocurrent densities of up to 100 A cm−2 have been determined.

Laser (λ = 809 nm) power converter based on GaAs

Laser-power converters with a wavelength of λ = 809 nm are fabricated on the basis of single-junction AlGaAs/GaAs heterostructures grown by the method of liquid-phase epitaxy (LPE). Photovoltaic modules with an operating voltage of 4 V for converting radiation of various densities are developed and tested. Two approaches—without the use of optical concentrating systems and with the use of Fresnel lenses are investigated. A monochromatic conversion efficiency exceeding 44% is attained with a photovoltaic module based on 64 laser-radiation converters 0.04 cm2 in area and a concentrating system made of a quartz-lens matrix.

Gas-fired thermophotovoltaic generator based on metallic emitters and GaSb cells

A prototype compact TPV generator with a propane burner (pressure 2 bar) and a metallic netted emitter has been developed and tested. A photovoltaic generator unit with 24 (1 × 1 cm2) GaSb cells has been fabricated. The fabrication technology of photovoltaic cells has been optimized. It is shown that the data obtained can be used to select the starting bulk material for fabrication of photovoltaic cells with similar output parameters. It has been experimentally demonstrated that, to achieve maximum efficiency, it is necessary, in addition to using photovoltaic cells with similar characteristics, to provide identical conditions of their operation (temperature, illuminance).