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We report on research carried out at the Ioffe Physical Technical Institute in the field of operational conditions of the high‐concentration photovoltaic (HCPV) module components. The subject of investigations are thermal regimes of the primary Fresnel lenses and multijunction solar cells. Two main issues governing the design of a solar concentrator module with III–V triple‐junction solar cells (SCs) are considered: the effective concentration of radiation using Fresnel lenses, and effective heat removal from SCs. By theoretical and experimental simulating these processes, the design parameters of modules’ elements have been found. A test batch of sub‐modules (HCPV modules based on individual Fresnel lenses) has been fabricated and tested. The influence of different operation temperatures on the optical efficiency of Fresnel lenses and conversion efficiency of solar cells have been estimated.

In the work, results of comparative investigation of the optical efficiency and power characteristics of concentrating systems with primary Fresnel lenses and secondary optical elements (SOE) are presented. The following types of the secondary optics are under consideration: an open truncated tetrahedral equilateral pyramid with specular walls and a kaleidoscope with a flat or convex top surface, which ensure achieving the high optical efficiency of a two‐element optical system, lowering its sensitivity to the Sun tracking inaccuracy and increasing uniformity of concentrated radiation distribution on a solar cell. As a result of the investigations carried out, the optimum parameters of the secondary optics have been determined, and the best optimal versions are recommended for practical usage in concentrator modules.

A solar TPV generator development and characterization are presented. A double stage sunlight concentrator ensures 4600x concentration ratio. TPV modules based on tungsten emitters and GaSb cells were designed, fabricated and tested at indoor and outdoor conditions. The performance of tungsten emitter under concentrated solar radiation was analyzed. Emitter temperatures in the range of 1400–2000 K were measured, depending on the emitter size. The light distribution in the module has been characterized, 1×1 cm GaSb TPV cells were fabricated with the use of the Zn‐diffusion and LPE technologies. The cell efficiency of 19% under illumination by a tungsten emitter (27% under spectra cut‐off at λ > 1820 nm) heated up to 1900–2000 K had been derived from experimentally measured PV parameters. The series connection of PV cells was ensured by the use of BeO ceramics. The possibilities of system performance improvement are discussed.

GaSb based structures were developed and fabricated by the Zn‐diffusion technique for thermophotovoltaic applications. Investigation of characteristics of cells for a conical system was carried out under a flash tester. Outdoor measurements of an array of three GaSb cells connected in parallel in a cylindrical system were carried out under illumination from tungsten emitters of different lengths. The maximum cylindrical system array photocurrent of 3.5 A has been obtained at the tungsten emitter temperature of 1400 °C. An optimum Zn diffused profile and penetration depth of p‐n junction have been found, which allowed to obtain the maximum efficiency of GaSb cells at high generated photocurrent density of up to 5 A/cm2. Study of the doping profile and characteristics of GaSb cells fabricated by means of a non‐traditional diffusion — from a solid state film diffusant — was performed as well. The external quantum yield of these cells was 0.82–0.87 at wavelength range of 800–1600 nm.

High efficiency TPV GaSb and Ge based cells fabricated by a non‐toxic and inexpensive Zn‐diffusion technique have been developed. GaSb based cells optimised for operation with solar powered photon emitter allowed increasing the efficiencies up to 27–28% at black body temperature > 2000 K assuming 90% reflection of sub‐bandgap photons. Combination of the MOCVD technique or LPE growth and Zn diffusion from the gas phase allows fabricating Ge photocells on the base of the GaAs/Ge heterostructures, which are characterized by high photocurrent and open circuit voltage values. Efficiencies of 13% were obtained in GaAs/Ge TPV cells under the black‐body (1700–2100 K) irradiation assuming the achieved 90% reflection of sub‐bandgap photons.

Solar thermophotovoltaic efficiency is theoretically estimated using the following optimisation parameters: sunlight concentration ratio, absorber/emitter temperature/efficiency, photon recirculation efficiency and TPV cell parameters. It has been found that emitter temperature exceeding 2000 K, absorber/emitter efficiency of 90% and TPV systems efficiency exceeding 30% can be obtained at sunlight concentration ratio exceeding 8⋅103 suns with using GaSb cells with back surface reflector and grey‐body emitter in vacuum. Utilization of the selective emitter allows to increase the efficiency: calculated efficiency of TPV system with tungsten emitter increases from 30% to 36%.

Developed solar TPV system consists of sunlight tracker, sunlight concentrator, absorber of concentrated sunlight, selective emitter of radiation, internal reflectors of radiation from the emitter, and PV cells cooled by water or forced air. The concentration ratio exceeding 8000 suns is ensured by the developed 300W dish mirror with secondary compound parabolic concentrator. The emitter is made of tungsten evacuated in a vacuum bulb. To decrease the losses of the photons emitted back to outside of TPV system, the area of the emitter surface exceeds up to 10 times the absorber aperture area. The developed PV cells based on Ge and GaSb have a back‐surface mirror, which reflects the sub‐bandgap photons to the emitter increasing its temperature and overall system efficiency.

Results of growth, material characterization and device performance of TPV cells based on Ge, Si, InGaAs/InP, GaSb, InGaAsSb, AlGaAsSb, InAsSbP and InAs fabricated by LPE, MOCVD, MBE and diffusion methods are presented. The highest efficiencies have been obtained in TPV cells based on GaSb and InGaAs (lattice matched to InP substrate): external quantum yield as high as 90% in IR‐part of photosensitivity spectrum; Voc=0.45–0.52 V; FF=0.7–0.8 at photocurrent densities of 1–5 A/cm2 and efficiency of more than 10% under available matched radiators. A low‐cost Zn‐diffusion technology for reproducible fabrication of p‐n‐GaSb structures has been developed for producing the high efficiency TPV cells being used for TPV generators. Growth of epitaxial lattice‐matched AlGaAsSb wide‐bandgap windows and InGaAsSb low‐bandgap (0.5–0.6 eV) photoactive layers on GaSb substrates, as well as a fabrication of tandem TPV devices based on GaSb top cells and InGaAsSb bottom cells should allow to improve the GaSb‐based cell perf...

We present the results of development of a TPV generator which may be considered as a prototype for a portable 5-20 watt TPV power supply using propane or butane fuel. The system of a cylindrical geometry consists of the following parts: burner; “gray” emitter at the temperature of about 1200 °C fabricated with high-temperature resistant metallic alloy; quartz window; PV array consisting of 15 series-connected GaSb cells surrounding the window. The cells of 2×1 cm2 in area are mounted on copper prisms having passively air-cooled aluminum fins. Generated photocurrent in the circuit of the TPV system is about 1.5A. Advanced cells on the base of liquid phase epitaxial GaSb material and lattice-matched InGaAsSb solid alloys (Eg=0.72–0.55 eV) are under development. External quantum yield as high as 90–96% was measured in such cells. Also, two-terminal monolithic tandem GaSb(top)/InGaAsSb(bottom) TPV devices with a built-in tunnel junction have been designed and fabricated. External quantum yields of 80–85% in ...

A decrease of AlGaAs layer crystallization temperature in LPE down to 550–400 °C allowed us to crystallize quantum wells as thin as 5–20 nm. Structures with a narrow‐gap active layer of 15 nm thick were used to fabricate separate‐confinement buried heterolasers. Low threshold currents Ith=2 mA in a continuous regime (300 K) were measured for lasers with 100 μm long cavities. The maximum external quantum efficiency of radiation was 68% for a laser with Ith=2.3 mA.