V.D. Rumyantsev

Solar thermophotovoltaic system with high temperature tungsten emitter

In this paper, R&D of a solar thermophotovoltaic (STPV) system is reported. Two types of TPV modules have been developed and tested under concentrated sunlight. Temperatures as high as 1800/spl deg/C were obtained in a 12 mm dia and 15 mm length emitter, illuminated by a 0.45 m/sup 2/ pseudoparabolic facet mirror with a secondary quartz lens (4000/spl times/ concentration ratio). Analysis of various parameters, influencing the overall performance of the developed STPV is presented.

Concentrator tandem solar cells based on AlGaAs/GaAs-InP/InGaAs(or GaSb) structures

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).

Tandem GaSb/InGaAsSb thermophotovoltaic cells

Computer modelling of a tandem thermophotovoltaic (TPV) system has been carried out. The monolithic GaSb/InGaAsSb tandem TPV devices have been designed and fabricated by LPE. The cell consists of: nGaSb (substrate); (n-p)In/sub x/Ga/sub 1-x/As/sub y/Sb/sub 1-y/ (E/sub g//spl ap/0.56 eV, bottom cell); p/sup ++/-n/sup ++/GaSb (tunnel junction); (n-p)-GaSb (top cell). External quantum yields of 80% at 800-1600 nm wavelength (top cell) and of about 75% at 1800-2100 nm (bottom cell) have been measured. V/sub OC/=0.61 V and FF=0.75 were achieved in a tandem cell at current density of 0.7 A/cm/sup 2/.

Progress In Developing HCPV Modules Of SMALFOC-Design

This work presents a module generation which has been named as “SMALFOC module design”. The abbreviation reflects the main features of the modules: Small-size concentrators; Multi-junction cells; “All-glass” structure; Lamination technology; Fresnel Optics for Concentration. Investigated modules have revealed a quite low over-heating temperature of cells in the MPP regime of operation and a real way for increasing the PV efficiency, if the rear glass base is supplied with an antireflection coating. Outdoor and high/low temperature tests have shown a good potential for long-term operation of such a type of modules.

Zinc-diffused InAsSbP/InAs and Ge TPV cells

By means of LPE growth and Zn diffusion, TPV cells and mid-IR photodetectors based on p-InAsSbP/n-InAsSbP/n-InAs and p-InAs/n-InAs structures have been fabricated with the photosensitivity widened in the infrared range (2.5-3.4 /spl mu/m). Zinc - diffused p-n Ge-based TPV cells have been fabricated with external quantum yield as high as 0.9-0.95 and high short circuit current of 31.6 mA/cm/sup 2/ under sunlight with cut-off at /spl lambda/< 900 nm AMO spectrum. The Ge-based TPV cells with back-surface mirror demonstrate reflection of 85% for the sub-bandgap photons. The Ge cells with GaAs window have been developed for PV and TPV applications with using the combination of liquid-phase epitaxy and Zn-diffusion processes. Efficiency of more than 5% has been measured in p-GaAs/p-Ge/n-Ge cells under cut-off (/spl lambda/<900 nm) AM1.5 spectrum at photocurrent densities of 3+20 A/cm/sup 2/.

Thermal Regimes of Fresnel Lenses and Cells in “All‐Glass” HCPV Modules

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.

Single-junction GaSb and tandem GaSb/InGaAsSb and AlGaAsSb/GaSb thermophotovoltaic cells

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.

Evaluation of the PV Cell Operation Temperature in the Process of Fast Switching to Open-Circuit Mode

A procedure for measuring the overheating temperature (ΔT ) of a p-n junction area in the structure of photovoltaic (PV) cells converting laser or solar radiations relative to the ambient temperature has been proposed for the conditions of connecting to an electric load. The basis of the procedure is the measurement of the open-circuit voltage (VOC ) during the initial time period after the fast disconnection of the external resistive load. The simultaneous temperature control on an external heated part of a PV module gives the means for determining the value of VOC at ambient temperature. Comparing it with that measured after switching OFF the load makes the calculation of ΔT possible. Calibration data on the VOC = f(T ) dependences for single-junction AlGaAs/GaAs and triple-junction InGaP/GaAs/Ge PV cells are presented. The temperature dynamics in the PV cells has been determined under flash illumination and during fast commutation of the load. Temperature measurements were taken in two cases: converting continuous laser power by single-junction cells and converting solar power by triple-junction cells operating in the concentrator modules.

Space Fresnel lens concentrator modules with triple-junction solar cells

The work presented in this paper is concerned with fabrication of an improved concentrator module based on linear Fresnel lenses and photoreceivers with GalnP/GaAs/Ge triple junction (TJ) cells. The manufactured module consists of: four linear Fresnel lenses with focal distance of 30 mm and dimensions of 2.5/spl times/10 cm/sup 2/ each; four linear photoreceivers of 10 cm in length with 12 TJ solar cells each; heat sink made of thin copper metallized dielectric plate. Linear Fresnel lenses with optical efficiency of 82-84% were made of silicone formed on shockproof radiation-resistant UV-protective glass 0.2 mm thick. The solar cells intended for use in linear receivers have efficiencies of 23-24% (AM0, 25 /spl deg/C) at geometrical sunlight concentration of 6-9/spl times/. The estimated module efficiency is about 21% (AM0).

Tritium-powered betacells based on Al/sub x/Ga/sub 1-x/As

The paper describes betavoltaic cells (BVC) based on A/sup 3/B/sup 5/ semiconductors. It is shown that wide band gap semiconductors such as AlGaAs ensure the efficient betavoltaic conversion of beta radiation from tritium and photovoltaic (PV) conversion of the light from tritium powered radioluminescent sources. Betavoltaic cells based on Al/sub x/Ga/sub 1-x/As with ultrathin (0.01-0.03 /spl mu/m) wide bandgap passivating window were developed. Output current densities as high as (0.75-1)10/sup -6/ A/cm/sup 2/, open circuit voltage of 0.65-0.93 V and maximum power output of 0.55 /spl mu/W/cm/sup 2/ were achieved in the betacells in a capsule with tritium gas. Specific output power of 335 nW/Ci is ensured in the battery based on green tritium lamps and developed PV cells.