This paper reports on the development and optimization of high-efficiency single-junction GaAs photovoltaic laser power converters (PVLPCs) designed for the 800–850 nm spectral range. The heterostructures have been grown by metalorganic vapor-phase epitaxy, and their photovoltaic parameters have been investigated under direct laser illumination. The study compares simplified upright-growth heterostructures with complex inverted-growth PVLPCs featuring integrated back reflectors. For the inverted structures, an efficiency of approximately 64% was achieved at an irradiance of 70 W/cm2. In contrast, the upright-growth heterostructures were optimized by balancing the absorber layer thickness and carrier collection efficiency, which was enabled by high minority carrier diffusion lengths exceeding 15 μm. Further optimization of the spreading layer thickness and front contact grid geometry allowed the upright-growth PVLPCs to reach a peak conversion efficiency of 66.1% at 70 W/cm2, while maintaining efficiencies above 60% up to 200 W/cm2. The study highlights that while inverted structures offer higher theoretical potential due to multiple photon passes, the optimized upright-growth technology provides superior practical performance. This makes the upright-growth approach highly competitive for high-power laser power beaming applications.

An experimental study on the luminescence properties of strained InGaAs/AlGaAs multiple quantum wells (MQWs) using strain-compensating layers (SCLs) based on quaternary AlGaAsP solid solutions was performed. Since the main goal was to implement these heterostructures in near-infrared LEDs (940 nm), they were grown using metalorganic vapor-phase epitaxy on vicinal GaAs substrates misoriented by 6° from the (100) surface. It was demonstrated that several theoretical models based on continuum elasticity theory can precisely predict the optimal SCL thickness required to achieve the highest photoluminescence performance of the MQWs. Furthermore, even the simplest calculation methods that neglect differences in material stiffness parameters are shown to be suitable for this estimation. Based on the optimized MQW active region, infrared LEDs were fabricated, exhibiting a peak external quantum efficiency exceeding 57%, an energy efficiency of over 63%, and an output optical power of approximately 80 mW at a current of 100 mA.

The paper presents an overview of studies of the multi-junction (MJ) solar cells (SC) with IV characteristics having nonlinear peculiarities. It is shown that such peculiarities can arise either due to hetero-interface barriers (HB) for majority charge carriers or due to problems with tunnel diodes (TD). It is usually difficult to identify which of these hetero-structural objects is the cause of this nonlinearity, since the peculiarities appear similarly in the IV characteristics of MJ SC. The experimental method presented in this work is based on the study of IV characteristics during the overheating of MJ SCs. The behavior of nonlinear peculiarities caused by an imperfect TD or an HB is fundamentally different during the overheating of SCs, which makes it possible to identify the type of hetero-structural object. Since the number of hetero-interfaces in MJ SC is large, a method determining the position of problematic objects in the MJ structure was also developed. The method is based on the illumination of individual subcells using different laser wavelengths. Both methods considered were tested experimentally on GaInP/GaAs/Ge SCs.

The method described in this article offers a simple and convenient way to obtain highly efficient, ultrathin, and flexible solar cells (SCs) based on III‐V/Ge heterostructures. This is achieved by thinning Ge to several tens, or even a few units of microns, which accounts for up to 95% of the total thickness and weight of a SC. The only low‐temperature thermal peelable tape REVALPHA as a temporary carrier supports and saves the heterostructure along the process route. The carrier is then easily and cleanly removed by heating without damaging the thinned SC. The temporary carrier provides a reliable transfer of the thinned SC with a developed low‐temperature (i.e., without annealing) indium back contact to an arbitrary light and flexible substrate (Kapton or carbon sheet). The possibility of creating highly efficient, ultrathin, and ultralight SCs on a flexible carrier is demonstrated using mass‐produced GaInP/Ga(In)As/Ge heterostructures. Based on the results obtained, a possible architecture and technology for assembling coupons from ultrathin solar cells based on any III‐V/Ge heterostructures on a Kapton or carbon carrier for space and terrestrial applications are proposed.

The optimization of present multijunction junction solar cells and the development of new concepts is an important task for modem photovoltaics. For its development, special attention should be paid to the potential quality of photoactive p-n junctions, as well as to their properties when operating at various temperatures. The present research has shown that for two-diode model of the p-n junction it is convenient to use current invariants Jz1 and Jz2 for calculating the diffusion and recombination saturation dark currents J01 and J02 for p-n junctions based on semiconductor materials with any band-gap energy. It has been experimentally found that Jz1 and Jz2 are constants relating the semiconductor material band gap energy and temperature with J01 and J02. It has also been shown that Jz1 and Jz2 determine the open circuit voltage and the value of voltage offset WOC. Current invariant suggested to be useful tool for evaluating the quality of a p-n junction and for modeling the characteristics of solar cells because it allows making calculations taking into account both main mechanisms of current flow and the operating temperature of the device.

Optimized photoconverters for operation under high-power laser radiation in the green-red spectral range based on MOCVD-grown GaInP/GaAs heterostructures are fabricated. The Au(Ge)/Ni/Au and Pd/Ge/Au contact systems have been studied to form the front contact grid of devices. As a result, the laser photoconverter with a Pd/Ge/Au contact showed an efficiency of more than 50% up to an incident radiation power density of 30 W/cm 2 with a maximum value of 54.4% under 7 W/cm 2 for laser line with wavelength of 600 nm. Keywords: photoconverter, laser radiation, MOCVD, efficiency, spectral sensitivity.

GaInP-based laser power converters (LPC) structure grown by MOVPE and device chip design have been optimized for operation under high-power lasers of the green-red spectral range. Light I-V curves records have shown the performance of the LPC at up to 40-50 W/cm2 of incident power densities. The highest level data were obtained for 532, 600, and 633 nm power laser lines: 44.3%, 46.7%, and 40.6% under 13-16 W/cm2, respectively. LPC demonstrated an efficiency of more than 40% at the incident laser radiation power density elevated up to 40-50 W/cm2. Keywords: laser photoconverter, MOVPE, efficiency, spectral response.

The effect of positioning of the In0.8Ga0.2As quantum dots (QDs) array in the i-region of the solar cell (SC) on its photogenerated current and dark saturation currents, which determine the device operating voltage, have been investigated. It was found out that the indicated photoelectric characteristics depend on the location of the QD array relative to the electric field of the p-n junction. The displacement of the QD array to the boundary of the weakly doped base leads to a decrease in the photogenerated current. But at the same time, the voltage drop effect, which is well-known for nanoheterostructural SC, is minimal. Keywords: solar cells, quantum dots, dark saturation current

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.

Developed and investigated are IR (850 nm) light-emitting diodes based on AlGaAs/Ga(In)As heterostractures grown by the MOCVD technique with multiple quantum wells in the active region and with a double optical reflector consisted of a multilayer Al0.9Ga0.1As/Al0.1Ga0.9As Bragg heterostructure and an Ag mirror layer. Light-emitting diodes with the external quantum efficiency EQE = 37.5

The results of a study of the angular dependence of the reflectivity of black silicon structures with conical and filamentary nanowires, and a silicon surface with a textured pyramidal surface coated with an ITО layer are presented. The possibility to increase the annual electricity generation for solar cells based on black silicon has been demonstrated due to the weak angle dependence of the total reflectance. Compared to the textured pyramidal surface, the increase is 7.34 and 6.33

The paper presents a promising solution for photovoltaic modules that provides overcoming the main conceptual limitation for the concentrator concept in photovoltaics—the impossibility to convert diffused (scattered) solar radiation coming to the panel of sunlight concentrators. The design of a hybrid concentrator-planar photovoltaic module based on heterostructure solar cells: A3B5 triple-junction and Si-HJT is presented. The results of initial outdoor studies of the module output characteristics are discussed and estimates of its energy efficiency are given.

In photovoltaic converters of concentrated sunlight, the thermal flow is directed from the photoactive region (p–n junction) to a heat-spreading basement through the substrate. The heat sink transfers the excess thermal to the environment by convection or cooled by a liquid carrier. Reducing the thickness of the substrate makes it possible to reduce the thermal resistance of the crystal and lower the operating temperature of the photoactive region. However, in this case, the mechanical stresses in it increase. This work discusses the balance between the mechanical strength of the sample and the decrease in its operating temperature.

The efficiency of GaInP/GaAs/InxGa1-xAs triple-junction solar cells obtained by replacing (in the widely used "classical" GaInP / GaAs / Ge heterostructure) the lower germanium with InxGa1-xAs subcell formed using the metamorphic growth technology has been investigated. Based on an original approach, the optimal indium concentration in the narrow-gap subcell has been found. The main parameters of InxGa1-xAs subcells with an indium concentration from x=0.11 to 0.36 were determined and were used to calculate the IV characteristics of GaInP/GaAs/InxGa1-xAs solar cells. It has been determined that at x=0.28 the efficiency of the triple-junction solar cell increases by 3.4% (abs) in comparison with the "classical" solar cell, reaching a value of 40.3% (AM1.5D). Also it has been shown that the efficiency of such solar cells can be increased up to 41%. Keywords: Multi-junction solar cells, photoconverters, metamorphic buffer. M.Z.Shvarts,

Photovoltaic conversion of laser radiation has found wide application in fiberoptic communication lines. Energy transfer via a laser beam is also relevant for remote power supply systems on Earth and in space. These systems can be used to power unmanned aerial vehicles, to transfer laser energy between spacecraft and from space solar panels to Earth. One of the main tasks in creating such systems is to ensure high efficiency of photovoltaic converters at high power (more than 100 W/cm2) of laser radiation. The article presents the results of research and development of photovoltaic converters of highpower laser radiation based on nanoheterostructures obtained by MOCVD epitaxy. The reduction of losses was achieved by embedding the “dielectric-silver” rear combined reflector into the structure. An increase in the generated voltage was achieved by shifting the volume charge region into the wide-gap layer of the p-GaAs-n-AlxGa1-xAs heterojunction. Thanks to an additional reduction in ohmic losses, efficiency values of 60 % have been achieved at laser radiation (λ = 860 nm) powers in the range of 50-400 W/cm2.

In high illumination conditions for photovoltaic converters, it is possible to stabi-lize the temperature of the photoactive region using a heatsink with high thermal conductivity, and by thinning the substrate that is a holder for semiconductor structure. However, the use of both methods together can lead to significant increase of the possible fragility of the con-verter. This work is devoted to the searching of balance between brittleness and overheating of GaAs/Ge solar cells installed on a copper heatsink with ceramic intermedia. Such composite heatsink, on the one hand, reduces mechanical stresses in the semiconductor, but, on the other hand, makes better the heat removal mode.

The Ge-based photovoltaic laser-power converters (LPCs) for wireless IR energy delivery approach with a wavelength of λ = 1550 nm are studied and developed. It is shown that the doping by diffusion from the gas phase with zinc gives rise to a notable increase in photosensitivity compared with the doping with diborane, phosphine, or antimony (including for two-stage diffusion technology). Four designs and areas of converters are fabricated and investigated under Xe flash lamp, defocused and focused laser beams. For LPCs with an area of 6.25 mm 2 , a monochromatic efficiency of ∼20% (0.2 W) is obtained at uniform irradiation.

In this work, we studied the influence of GaP compensating layers on the characteristics of GaAs solar cells with InGaAs quantum dot arrays. An increase in the overall level of quantum efficiency in the absorption range of quantum dots (870-1000 nm) by more than 10% has been demonstrated when GaP layers are embedded in GaAs intermediate layer (spacer) of a quantum dot array. It was also shown that in this case a noticeable increase in the open-circuit voltage can be achieved at high solar concentration.

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.