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We have studied the dynamics of air humidity in the interior of a concentrator photovoltaic (CPV) module equipped with air-drying device filled with moisture-absorbing material based on silica gel. A new design of the air-drying device was developed for preventing the deposition of condensate onto the surfaces of a Fresnel lens, solar cell, and CPV module. Under unfavorable ambient conditions (relative humidity up to 95%), this device allowed to reduce the inner humidity to 25–55% at cyclic temperature variation within 15–45°C and to increase the dew point deficit up to 10–25°C.

Methods for passivation and protection of p–n junctions at places of their emergence at the lateral surface of a mesa structure and for sealing-off of multijunction solar cells based on a GaInP/GaAs/Ge structure have been studied. Protective coatings based on silicon nitride and silicone layers were examined by analyzing dark current–voltage characteristics of the solar cells. The distribution of the electroluminescence was analyzed.

High-efficiency concentrator photovoltaic modules have been developed and fabricated. The modules include a lens panel based on 32 Fresnel lenses (12 × 12 cm each), 32 multi-junction solar cells with secondary concentrators in the form of phocons, and heat-removing electrically insulating boards based on an aluminum oxide ceramic placed on the backside aluminum base. Efficiency measurements of a 0.46-m2 module under a pulsed sunlight simulator (AM1.5D, 1000 W/m2) yielded a value of 32.3%. An efficiency of 33.9% was obtained for a subunit with an area of 144 cm2.

The results of studies of characteristics of heat-removing electrical insulating plates of different designs based on heat-conducting AlN and Al2O3 ceramics and aluminum-oxide plates based on aluminum plates are presented. Thermophysical parameters of the heat-removing plates were assessed by measuring the temperature of p–n junctions of the photoelectric converters mounted on the plates with thermal load applied to them. It was found that the minimum overheating temperature of p–n junctions, 45°C, was observed at the supplied thermal power of 13 W, when the photoelectric converters were installed on the AlN ceramics. In photoelectric converters installed on the Al2O3 ceramics, the overheating of p–n junctions was 49°C, while it reached 70°C on the aluminum-oxide substrate.

Spectral characteristics of the Ge subcell of triple-junction GaInP/GaAs/Ge solar cells have been simulated. It was shown that using a GaInP nucleation layer that creates a shallow diffusion p–n junction in Ge can raise the photogeneration current of the Ge subcell by ~4.5 mA/cm2 as compared with the value in the case of a GaAs nucleation layer. The optimal thickness of the GaInP layer (170–180 nm) makes it possible to additionally raise the photocurrent by ~1.5 mA/cm2. It was experimentally demonstrated that the photogenerated current of the Ge subcell of GaInP/GaAs/Ge solar cells increases by 3.9 mA/cm2 on replacing the GaAs nucleation layer with GaInP and there is an additional gain by 0.9 mA/cm2 on using the optimal thickness of the GaInP nucleation layer.

High-efficiency photovoltaic converters (PVCs) have been developed and fabricated by liquidphase epitaxy in the AlGaAs–GaAs system with laser light (λ = 850 nm) introduced through the edge surface in parallel to the plane of the p–n junction of the device structure. To raise the efficiency of light “capture” by the p–n junction, an AlxGa1–xAs waveguide layer is formed, in which the content of aluminum gradually varies from x = 0.55 to 0.15 so that the refractive index gradient is created in this layer and light beams are diverted toward the p–n junction. When a PVC (having no antireflection coating) is exposed to 0.1- to 0.2-W laser light, an efficiency of 41.5% is obtained. Depositing an antireflection coating on the edge surface of a PVC raises its efficiency to 55%.

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.

The insertion of quantum dots in a host material produces band offsets which are greatly dependent on the field of strains brought about by this insertion. Based on the Empiric KP Hamiltonian model, the energy spectrum of the quantum dot/host system is easily calculated and a relationship between the conduction and valence band offsets is determined by the energy at which the lowest peak of the sub-bandgap quantum efficiency of an intermediate band solar cell is situated; therefore knowledge of the valence band offset leads to knowledge of both offsets. The calculated sub-bandgap quantum efficiency due to the quantum dot is rather insensitive to the value of the valence band offset. However, the calculated quantum efficiency of the wetting layer, modeled as a quantum well, is sensitive to the valence band offset and a fitting with the measured value is possible resulting in a determination of both offsets in the finished solar cell with its final field of strains. The method is applied to an intermediate-band solar cell prototype made with InAs quantum dots in GaAs.

The aim of the study is to apply a method commonly used to determine the efficiency of multi� junction nanoheterostructure III-V solar cells by analysis of the dark current-voltage (I-V) characteristics to such an unconventional semiconducting material as amorphous silicon. aSi:H and aSi:H/ μcSi:H p-i-n structures without a lightscattering sublayer or an an tireflection coating are studied. The results of measure� ments of the dark I-V characteristics demonstrate that the voltage dependence of the current has several exponential portions. The conversion efficiency of solar cells (SCs) is calculated for each portion of the dark I-V characteristic. This yields a dependence of the potential SC efficiency on the generation current density or on the photon flux. The observed agreement between the data derived from the experimental characteris� tics and results of calculations can be considered satisfactory and acceptable, thus the method suggested for measurement and analysis of dark I-V characteristics and tested earlier on SCs based on crystalline III-V compounds acquires a universal nature. The analysis of the characteristics of p-i-n amorphous silicon structures and the calculation of potential efficiencies, based on this analysis, extend the authors' understanding of this class of devices and make it possible to improve the technology and photoconversion efficiency of SCs of this kind.

Photovoltaic converters based on nGaInP/ n-pGe heterostructures grown by the OMVPE under different conditions of formation of the p-n junction are studied. The heterostructures are intended for use as narrowgap subcells of the GaInP/GaInAs/Ge threejunction solar cells. It is shown that, in Ge p-n junc� tions, along with the diffusion mechanism, the tunneling mechanism of the current flow exists; therefore, the twodiode electrical equivalent circuit of the Ge p-n junction is used. The diode parameters are determined for both mechanisms from the analysis of both dark and "light" current-voltage dependences. It is shown that the elimination of the component of the tunneling current allows one to increase the efficiency of the Ge subcell by ~1% with conversion of nonconcentrated solar radiation. The influence of the tunneling current on the efficiency of the Gebased devices can be in pr actice reduced to zero at photogenerated current density of ~1.5 A/cm 2 due to the use of the concentrated solar radiation.

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.

The isovalent dopant diffusion from a localized source method was applied for the surface and bulk passivation of In 0.53 Ga 0.47 As (InGaAs) and GaAs layers. The passivation effects are characterized by low-temperature (77 K) photoluminescence (PL) spectroscopy. It has been found that phosphorus and/or indium doping from the gas phase increases effectively the PL intensity of InGaAs and GaAs layers. The phosphorus and indium diffusion into thin (∼100 nm) GaAs layers grown on the Ge substrate was carried out. The PL spectrum of these layers consists normally of a broadband emission line at ∼1.2 eV associated with the donor–acceptor pair recombination. Both donors and acceptors in GaAs are usually assigned to diffuse from the substrate Ge atoms occupying both Ga and As sites. Drastic changes of the PL emission after the phosphorous diffusion were observed: the intensity of the photoluminescence increases gradually, and the blueshift observed with the pumping energy increase is more pronounced. These changes are explained by a decrease in the nonradiative charge carrier recombination rate (e.g. at the GaAs–Ge heterointerface) by incorporation of phosphorus and indium atoms into GaAs during diffusion. This passivation method opens a promising way to improve the characteristics of multi-junction solar cells on Ge substrates.

The effect of the properties of interfaces with Group-III phosphides on characteristics of GaInP solar cells has been studied. It is shown that the large valence band offset at the p-GaAs/p-AlInP interface imposes fundamental limitations on the use of p-AlInP layers as a wide-band-gap window in p-n structures of solar cells operating at ratios of high solar light concentration. It is demonstrated that characteristics of p-n solar cells can be, in principle, improved by using a double-layer wide-band-gap window constituted by p-Al0.8Ga0.2As and p-(Al0.6Ga0.4)0.51In0.49P layers.

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).

Dependence of the efficiency of single-junction and multijunction solar cells on the mechanisms of current flow in photoactive p-n junctions, specifically on the form of the dark current-voltage characteristic J-V, has been studied. The resistanceless J-Vj characteristic (with the series resistance disregarded) of a multijunction solar cell has the same shape as the characteristic of a single-junction cell: both feature a set of exponential portions. This made it possible to develop a unified analytical method for calculating the efficiency of singlejunction and multijunction solar cells. The equation relating the efficiency to the photogenerated current at each portion of the J-Vj characteristic is derived. For p-n junctions in GaAs and GaSb, the following characteristics were measured: the dark J-V characteristic, the dependence of the open-circuit voltage on the illumination intensity P-VOC, and the dependence of the luminescence intensity on the forward current L-J. Calculated dependences of potential efficiency (under idealized condition for equality to unity of external quantum yield) on the photogenerated current for single-junction GaAs and GaSb solar cells and a GaAs/GaSb tandem are plotted. The form of these dependences corresponds to the shape of J-Vj characteristics: there are the diffusion- and recombination-related portions; in some cases, the tunneling-trapping portion is also observed. At low degrees of concentration of solar radiation (C < 10), an appreciable contribution to photogenerated current is made by recombination component. It is an increase in this component in the case of irradiation with 6.78-MeV protons or 1-MeV electrons that brings about a decrease in the efficiency of conversion of unconcentrated solar radiation.

Using the Hall method, regularities of Te doping of GaSb grown by the Czochralski method and by liquid-phase epitaxy (LPE) are studied. Optimum epitaxial conditions that enable the growth of Te-doped GaSb layers with higher carrier mobilities than the bulk Czochralski-grown GaSb are determined. Possibilities of improvement of output parameters of photoconverters obtained by diffusion of Zn into n-GaSb from the gas phase and by LPE are discussed.

The analysis of photoelectrical properties of heterostructure solar cells biased on GaInP is performed using a numerical modelling. The influence of AlInP/GaInP and AlGaAs/GaInP interface parameters and properties of AlInP layer on solar cells characteristics is shown. In particular, a crucial role of the band offsets and of interface states in defining the solar cell efficiency is demonstrated. The observed difference in photovoltaic performance of p–n versus n–p junctions is explained in terms of the parameters outlined above. The simulation results are supported by experimental data.

This study was aimed at the development of a method for detection of colonies of nuclease-secreting marine bacteria. The BAL nuclease-producing marine bacterium Pseudoalteromonas espejiana BAL-31 was used as the test object. A new method was developed involving the congo red (CR) anionic dye. The P. espejiana culture was plated on nutrient agar with CR and denatured DNA. In such media, CR was found to form complexes with DNA. After two days of incubation at 30°C, halos were found around the P. espejiana colonies. No halos appeared when DNA was not introduced, when BAL nuclease was inactivated, or when the plates were inoculated with Escherichia coli. It was concluded that the halos around the colonies indicated nuclease secretion. The halos were shown to result from the coagulation of CR released after digestion of the CR-DNA complex by the nuclease. This method for detection of nuclease-producing colonies can probably be used for all marine bacteria and possibly for halophilic bacteria as well.

DNA of bacteriophage PM2 is a convenient test object for studying DNA-damaging genotoxic agents. The extent of DNA damage can be estimated by the ability of damaged DNA for transfection of host cells, marine bacterium Pseudoalteromonas espejiana (Pae), str. BAL-31. The efficiency of transfection of Pae lines maintained for long periods without freezing was found to be very low upon the use of a widely accepted transfection method developed by van der Schans et al. (1971). Such cultures grown in a medium with 10 mM Ca2+ standard for Pae contained cell aggregates and exopolymer material. Pae was found to be capable of growing in a medium without the calcium supplement in the presence of chelator EGTA (low-calcium medium, LCM). After growth in LCM, cells did not aggregate, cultures lacked the activity of nuclease BAL, and transfection efficiency of cells grown in LCM drastically increased. Based on these results, a novel procedure of transfection with an efficiency of 2 × 104−2 × 105 infectious centers per microgram of PM2 DNA was developed.

In the present work, high efficient photovoltaic (PV) cells based on gallium antimonide have been developed and fabricated with the use of the liquid phase epitaxy (LPE) and diffusion from the gas phase techniques. They are intended for conversion of the infrared (IR) part of the solar spectrum into electricity by tandems of mechanically stacked cells and for conversion of the thermal radiation of emitters heated by the sunlight. On the ground of investigation of the LPE temperature regimes and the tellurium doping effect, GaSb PV cells have been fabricated with the efficiency of 6% at the concentration of 300 suns behind the single-junction GaAs top cell and of 5.6% at the same sunlight concentration of the cells behind the dual-junction GaInP∕GaAs structure, the substrate thickness being 100μm (the efficiency of PV cells was calculated for AM1.5D Low AOD spectrum, 1000W∕m2). The rated efficiency of conversion of solar powered tungsten emitter radiation by PV cells based on gallium antimonide in a thermophotovoltaic (TPV) module appeared to be about 19%. Photovoltaic cells based on germanium with a wide-gap GaAs window grown by LPE or metalorganic chemical vapor deposition and with a p-n junction formed by means of the zinc diffusion from the gas phase have been fabricated. Ge based PV cells without a wide-gap GaAs window had the efficiency of up to 8.6% at a concentration of 150 suns. The efficiency of Ge based cells with a wide-gap GaAs window was 10.9% at the concentration of 150 suns. 4.3% efficiency Ge cells behind a single-junction GaAs top cell at the concentration of 400 suns have been also obtained. The maximum rated conversion efficiency of Ge PV cells appeared to be about 12% in the case of conversion of the tungsten emitter thermal radiation. These efficiency values for Ge based cells are among the highest.

A GaAs solar cell without prismatic covers, with the highest efficiency known to the authors in the range of 1000-2000 suns for a single junction, is presented. Low temperature liquid phase epitaxy is used for its growth. In addition to improvements such as the achievement of a good quality material or a low contact resistance, this solar cell exhibits specific enhanced aspects. Among the most noticeable are: (1) an innovative design; (2) a double and gradual emitter layer; (3) a small size: 1 mm/sup 2/, (4) a finger width of the front metal grid of 3 /spl mu/m; and (5) a tailored ARC deposition based on a nondestructive and accurate AlGaAs window layer characterization. As a consequence, an efficiency of 26.2% at 1000 suns and 25.0% at 2000 suns AM1.5D (standard conditions) is achieved thanks mainly to a short-circuit current density at 1000 suns of 26.8 A/cm/sup 2/ (and 53.6 A/cm/sup 2/ at 2000 suns) with a simultaneous series resistance of 3 m/spl Omega//spl middot/cm/sup 2/.

An investigation of the low-temperature liquid-phase epitaxy (LTLPE) process at 400–650 °C for crystallization of AlGaAs heterostructures with ultrathin (2–100 nm) layers has been carried out. In particular, low-threshold quantum-well heterolasers (threshold current density j th as low as 120 A cm −2 ) and high-efficiency solar cells (efficiency as high as 24.0–24.7% under AMO conditions at concentration ratio 20–100 ×) have been fabricated by LT LPE.

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.

In this work, LPE, MOCVD and Zn-diffusion techniques for GaSb, InGaAsSb and GaAs/Ge structures were applied for manufacturing the thermophotovoltaic (TPV) cells. Studies of the cells were carried out by a flash tester as well as under SiC and tungsten emitters, heated by radiation from a high power xenon lamp in a concentrated sunlight simulator. Maximum short circuit current density of 9 - 10 A/cm2 has been achieved in the cells.

This work reports on various approaches to illuminated I-V curve measurements in monolithic dual and triple-junction GaInP/GaAs/Ge cells with the aim of revealing the action of interconnecting tunnel diodes. The measurements were performed both for model samples using a combination of individual sub-cells, connected through an external tunnel diode and for practical concentrator cells with different peak current densities (Jp) of the tunnel diodes in a monolithic structure. Changing of load resistance, or changing of applied voltage from an external source, characterized by variable resistance, was used to obtain I-V curves under both continuous and flash illumination. Also, variation of cell internal resistance due to the current mismatch in sub-cells, caused by illumination spectrum variation, was proven by these measurements.

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%.

We present the use of small-aperture, linear and point-focus composite Fresnel lenses in space and terrestrial photovoltaic modules based on III-V solar cells. These lenses combine the positive features of conventional silicate glass and a stable polymer material such as silicone rubber. Optical efficiency measurements have been carried out on practical samples of "terrestrial" concentrators with varying lens' focal distance and aperture, as well as the receiver diameter. Introduction of small-size secondary lenses integrated in an intermediate panel with composite structure (glass plate + convex silicone lenses) allows one to improve the parameters of a concentrator system at high concentration ratios.

An improvement of the p-AlGaAs-p-GaAs-n-GaAs solar cells (SC) by decreasing the p-GaAs and p-AlGaAs thicknesses up to 0.3 mu m and 100 AA, respectively, is discussed. The drop in photocurrent in the SC after 6.7 MeV proton bombardment at a dose of 6*10/sup 12/ cm/sup -2/ was less than 10%. Additional ways to decrease the concentration of radiation-induced defects in the SC are injection (due to current flow) and photon (due to photoexcitation) annealing. These processes have been realized during operating of SC converting 15-100-fold concentrated sunlight. >

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...

The work presents an investigation of solar cells (SCs) based on AlGaAs/GaAs heterostructures with internal Bragg reflectors grown by low-pressure MOCVD on n-GaAs substrates in a horizontal resistively heated reactor. The typical structure consists of: Bragg reflector (BR) having 12 periods, n-GaAs base layer with the thickness of 1500-2000 nm, 400-500 nm thick p-GaAs emitter, 70 nm thick p-AlGaAs passivating window and top p-GaAs contact layers. The BR with the reflectance maximum centered at the wavelength of 860 nm consists of twelve pairs of AlAs/GaAs layers. The resulting BR thicknesses is 71.6 nm for AlAs and 59 nm for GaAs. In this case the peak of reflectance spectrum is in the area of 830-900 nm where the reflectance is close to unit. This multi-layer quasi-dielectric stack selectively reflect weakly absorbed photons with energies near the GaAs band gap for a second pass through the photoactive region increasing the photocurrent. The employment of the BR allows to increase the external quantum efficiency in the long wavelength range of the spectrum and to fabricate simultaneously a thinner n-GaAs base layer. The use of the internal BR, Ta/sub 2/O/sub 5/ for antireflecting coating and prismatic cover allowed us to obtain efficiency of 23.4% (17.7 suns, AMO, 25/spl deg/C) and 27.2% (23.4 suns, AM 1.5).

Due to the development of the low-temperature (T=450-650/spl deg/C) LPE and low-temperature Mg-diffusion processes, AlGaAs-GaAs heterostructure solar cells (SCs) with ultra-thin wide-gap "window" layers have been fabricated. A conversion efficiency as high as 24.6% under AM 0 conditions at the concentration ratio of 105 Suns has been measured on SC samples with a one-layer antireflection coating and a prismatic cover. A conceptual design and experimental results on space power application concentrator modules for the developed SCs are also presented. Based on reflective optics (light-weight compound parabolic concentrators (CPCs) or linear-focus parabolic troughs) these modules have to provide the specific parameters of 240 Watt/spl middot/m/sup -2/ and 3 kg/spl middot/m/sup -2/.

We have developed high-efficiency IR-transparent AlGaAs/GaAs top cells as well as InP/InGaAs and GaSb bottom cells for mechanically stacked tandem solar cells designed for space application. AlGaAs/GaAs and InP/InGaAs structures are prepared by liquid phase epitaxy, GaSb structures-by Zn-diffusion process. The highest top cell efficiency is 23.8% (AMO, 100 suns, 25/spl deg/C). The infrared-sensitive InP/InGaAs cell efficiency measured under a GaAs IR-filter is 5.9%. The maximum GaSb cell efficiency under GaAs-filter is 5.1%. Mechanically stacked four-terminal tandem solar cells have been fabricated and tested as well. The reached efficiency of an AlGaAs/GaAs-InP/InGaAs tandem cell is 28.2% (AMO, 70 suns, 25/spl deg/C).

The module has a dimensions of 2.5/spl times/10/spl times/10 cm/sup 3/ and consists of four Fresnel lenses with dimensions of 2.5/spl times/10 cm/sup 2/ each. Two photoreceiver strings are made of tandem GaAs/GaSb triplets and two strings are made of AlGaAs/GaAs single junction cells. The best fabricated GaAs/GaSb tandem cell efficiency of 27.5% (AM0, 10 suns, 25/spl deg/C), triplet efficiency of 25.6% (11 suns) and linear (10 cm in length) receiver efficiency of 24.3% (AM0, 6 suns, 25/spl deg/C) were received. Fresnel lens efficiencies of 0.82-0.85 were achieved. The estimated module efficiency is 21% (AM0, 25/spl deg/C). Module specific weight of 3 kg/m/sup 2/ was realized.

The advanced technology of the single- and dual-junction TPV cells, based on GaSb was developed. Photocurrent density as high as 54 mA/cm/sup 2/ under AM0 spectrum, efficiencies of 12.8% (AM1.5D, 120 suns) and 19.1% under cut-off AM0-spectrum (/spl lambda/=900-1800 nm) were obtained. The deviations of V/sub oc/ and FF in the GaSb 1 cm/sup 2/ cells are in the following ranges: V/sub oc/=0.42-0.45 V and FF=0.7-0.72 at photocurrent of 1 A. The cells of 2 cm/sup 2/ in area generate photocurrent up to 9 A at V/sub oc/=0.52 V. Tandem InGaAsSb (0.55 eV)/GaSb cells with V/sub oc/=0.65 V at I/sub sc/1A/cm/sup 2/ were developed. Tandem AlGaAsSb(1 eV)/GaSb cells with expected V/sub oc/=1.1 V at I/sub sc/=1A/cm/sup 2/ are under development as well.

Concentration using III-V solar cells is one of the best approaches to reduce PV costs. Consequently, the general purpose of this work is the achievement of the highest efficiency at 1000 suns with an enhanced LT-LPE (low temperature liquid phase epitaxy) growth method presenting several advantages such as low cost, lack of contaminants and easy industrialisation. Results of different batches of GaAs LT-LPE terrestrial concentrator solar cells manufactured are presented, compared and thoroughly discussed. The study is focused on the variation of the semiconductor structure, manufacturing process and encapsulation that resulted in an efficiency of 26.2% at 1004 suns (measured at NREL and assuming linearity of short-circuit current with irradiance). This efficiency is to our knowledge the highest in the world for a single junction solar cell at the 1000-2000 concentration range.

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 practical design has been developed for string-type PV receivers intended to operate in space application line-focus concentrator modules. MOCVD grown AlGaAs/GaAs solar cells are used in these receivers as the main elements whereas Zn-diffused GaSb solar cells are used in tandem to improve total efficiency. Secondary cylindrical lenses operating similar to a "large scale prismatic cover" and transforming a focal light line into separated spots are introduced on the surfaces of solar cells. Efficiency 18.3% (AM0, 15 Suns, RT) has been measured on the receiver 72 mm long constructed from twelve series-connected AlGaAs/GaAs solar cells.

The paper presents the results of the development of AlGaAs/GaAs and GaSb cells, manufactured for tandem solar cells and designed for point and line-focus concentrator modules. The maximum efficiency of 23-23.6% (25/spl deg/C, AM0) under 20-70 suns was achieved in the AlGaAs/GaAs infrared transparent cells with prismatic cover. The efficiency of 27.5% under AM1.5, 140 suns has been achieved. The cells based on GaSb homo-junctions, Zn-diffused structures have been developed for tandems and thermophotovoltaic (TPV) applications. AM1.5 efficiencies as high as 6.7% behind the GaAs filter for concentration ratio of 240 suns were achieved. Lattice matched p-n InGaSbAs-InGaSb heterostructures have been fabricated Zn-diffusion method. The long wavelength edge of photosensitivity of these cells is 2.15-2.2 /spl mu/m.

It is shown that the radiation resistance of the AlGaAs-GaAs heteroface solar cells (HSC) can be considerably improved due to optimum design. pAl0.8Ga0.2As-pGaAs-nAlyGa1-yAs (0

Summary form only given. The authors report on low-threshold quantum-well AlGaAs heterolasers emitting at wavelengths of 730-850 nm. A special LPE (liquid-phase epitaxy) technique has been developed to crystallize thin layer AlGaAs heterostructures in the low-temperature range of 400-600 degrees C. Values of threshold current density as low as 120 A/cm/sup 2/ at emitting wavelength lambda =845 nm and 380 A/cm/sup 2/ at lambda =760 nm were measured for wide-stripe geometry separate confinement lasers with 15-nm-thick active layers. 'Twice-buried' stripe laser heterostructures were developed to considerably narrow the width of the current channel, to confine the optical mode in lateral directions, and to compensate for the strain tensions in the active layer in order to solve the laser lifetime problem. Threshold currents as low as 2 mA at lambda =845 nm and 10 mA at lambda =765 nm were measured for 'twice-buried' stripe lasers without reflecting coatings on the facets (CW; T=300 K). The estimated lifetime was over 20000 h at room temperature. >

The role of oxygen in the process of doping GaN by Zn is established. It is shown theoretically and experimentally that Zn is dissolved in GaN in the form of complexes ZnO when oxygen or water vapour is present in the ambient of the growth reactor. Most of the complexes are neutral. Only the small part of Zn introduced is situated in electrically active positions. This fact can explain the enormously high Zn concentration which is necessary to obtain the compensation of GaN native donors. The electrical and luminescence properties of GaN epitaxial layers doped by Zn are given and the relation of these properties to the growth and doping conditions are considered. [Russian Text Ignore]

The thermal decompositions of the even silver dicarboxylates from silver oxalate to silver sebacate were studied. In vacuum, the dicarboxylates decomposed to give metallic silver, CO2 and organic diradicals as primary products, and polymers as secondary products. The higher silver dicarboxylates were much more stable to thermal treatment than silver oxalate, probably due to the initiation of decomposition of all carboxylates except silver oxalate by the rupture of a Ag-O and not a C-C bond.

1. The 7-methoxy-1,2-bis-(hydroxymethyl)-hydrophenanthrenes (VI), (VIII), (IX), and (X) have been synthesized by the lithium aluminium hydride reduction of the dimethyl esters of cis-cis-Δ4- and cis-Δ4a(10a)-7-methoxyhexahydrophenanthrene-1,2-dicarboxylic acids (V) and (VII) and the dimethyl esters of cis-syn-cis- and cis-anti-cis-7-methoxyoctahydrophenanthrene-1,2-dicarboxylic acids (XI) and (XIII). 2. The hydrogenation of the 7-methoxy-1,2-bis-(hydroxymethyl)-hexahydrophenanthrenes (VI) and (VIII) over 30%Pd/SrCO3 takes place spatially non-selectively and leads to a mixture of the two possible geometrical isomers of 7-methoxy-1,2-bis-(hydroxymethyl)-octahydrophenanthrene.

1. A study was made of the oxidation of the anhydride and diester of syn-cis-1,2,3,5,6,7,8,8a-octahydro-1,2-naphthalenedicarboxylic acid (I) and (XXIV) by peroxyacetic acid and it was shown that this reaction proceeds in the two possible steric directions with the formation of equal amounts of the corresponding isomericα- andβ -oxides. 2. The configurations of the isomeric oxides (II), (III) and (XXVI) were demonstrated by a series of chemical conversions and a study was made of some of their stereospecific conversions, which were con firmed by an examination of molecular models. 3. It was shown that theα-oxide (II) is capable of ready trans-diaxial opening of the oxide ring at the C-O bond at C10 with the formation of the 4-hydroxy-γ -lacto acid (IV), while theβ -oxide (III) is more stable and during a similar reaction undergoes opening of the oxide ring at the C4 bond with inversion of the configuration at this carbon atom. 4. An investigation was made of the reactions ofβ -oxides (III) and (XXVI) with hydrogen chloride, leading to the formation of trans-chlorohydrins (XVI) and (XIX), capable of lactonization into the corresponding 4-chloro-γ -lacto acids (XVII) and (XVIII) of the trans-decahydronaphthalene series, whose configurations corresponded to the 4-hydroxy-γ -lacto acid (IV).

1. A study has been made of the lactonization of the cis-1,2,3,5,6,7,8,8a-octahydromethyl-1,2-naphthalene-dicarboxylic acids (I) and (II), and also of the cis diesters (VI) and (VII), and evidence relating to the structures of the resulting cis lactone acids (III) and (XV) has been presented. 2. It has been shown that, of the epimeric trans acids (VIII) and (XX), only the trans acid (VIII) is capable of undergoing lactonization — a result in accord with the spatial configuration of (VIII)_. The trans acid (XX) and the trans acids (IX) and (XIX), which have inter-ring double bonds, are incapable of lactonization. 3. An examination of molecular models has provided an explanation of the experimentally observed steric hindrance to the lactonization of the trans-octahydromethyl-1,2-napthalenedicarboxylic acids (IX), (XIX), and (XX).

1. An apparatus for investigating the kinetics of rapid reactions in solution by the stopped-jet method, permitting the recording of reactions with half-conversion times greater than 1 msec according to the change in the optical density in the ultraviolet or visible region, was described. The jet portion is made as an attachment to an SF-4 spectrophotometer. 2. An example of measurement of the rate of complex formation between molybdate and propyl gallate on this apparatus was cited.