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Computational nanotechnology
1-2017
ISSN 2313-223X
7.2. PROPERTIES OF GaAs/AlGaAs HETEROPHOTOTRANSFORMATORS WITH HOLOGRAPHIC CONCENTRATORS
Abdukadirov Muhitdin Abdurashitovich, Dr. of sciences, Professor, Tashkent University of information Technologies
Azamatov Zakir Tahirovich, Dr. of sciences, Professor, Tashkent State Technical University
Axmedova Nodira Aminjanovna, Candidate of science, Tashkent University of information Technologies
Ganiyev Abror Sattarovich, Candidate of science, Tashkent University of information Technologies, e-mail: abror1958@gmail.com
Muminov Ramizulla Abdullaevich, Academician Uzbekistan Academy of sciences Physical-Technical Institute «Physics-San» Uzbekistan Academy of sciences
Abstract: Studied photovoltaic processes in GaAs /AlGaAs heterostructure solar cell with a spectral sensitivity in the range of 450 < X< 850 nm under holographic concentrator illumination. It is shown that with increasing of concentration of the solar flux to 10krat with a linear increase in short-circuit current and open circuit voltage efficiency reaches its maximum value.
Index terms: solar sell, semi conduction, gallium arsenide, spektrowave diapazon, short circuit current, open circuit voltage, hologhraphic concentrator.
Photovoltaic conversion of solar energy into electricity is currently receiving increased attention [1]. However, the usage of holographic concentrators [2, 3] to create a photovoltaic system is a promising direction of solar energy, except as they are lightweight construction, does not require tracking of the sun system. At the same time, the basic properties of the photoelectric heterophoto-transformators (HPhT), with holographic concentrating systems, hardly been studied up to these days [3].
In this study, we investigated HPhT with heterostructure nGaAs/pGaAs /pAlxGa1-xAs (x=0,8), where the base layer pGaAs obtained by low-temperature diffusion of Zn from the gas phase prior to formation of the solid solution pAlxGa1-xAs by liquid phase epitaxy on nGaAs substrates. The electron density in the source of nGaAs was ~2.1017 cm-3 and in the layers and pGaAs u pAlxGa1-xAs (1...3)1017 cm-3 and 3...5 1018 cm-3 respectively. Thickness of the heavily doped base layers, and were within 5.10 mcm u 3.5 mcm respectively. The ohmic contacts are deposited by chemical vapor deposition of Ag stripe form on the surface of a solid solution pAlxGa1-xAs and solid form on the end face of the heterostructure, followed by thermal annealing at 675K. On the front surface of HPhT marked as antireflection layers on the basis of SiO2. Investigated HPhT had a total area of ~0,25 cm2. Holographic Lighting-concentrating system is installed parallel to the plane in which the surface of the photodetector of HPhT is located[3].
The degree of concentration of solar radiation Kc were determined from the dependence of the photocurrent Iph by incident radiation energy E Iph = f(E). When exposed to a holographic concentrator is a change light levels up to 8000 W/m2. This means that the degree of concentration of solar radiation may reach Kc = 10. With such Kc properties HPhT values can be studied without forced cooling mode (cooling HPhT performed due to thermal radiation from the front and back surface, and heat - only by exposure to solar radiation).
As studies have shown, in such a range of the Kc will be the equations of a thin p-n transition theory, according to which the short-circuit current is approximately equal to the photocurrent and increases proportionally with changes in light level, where there is a so-called linear photoelectric process [4]
Ishc = Ishc Kc=1 Kci (1)
where Ishc Kc=1 - short-circuit current in the absence of the concentration of the solar flux.
The dependence of the open circuit voltage of the degree of concentration of the solar flux is described by
Vir = Vir + kT/q (K/Kco), (2)
where K0 - the initial concentration of solar radiation.
When exposed to the concentrated solar radiation occurs ohmic field increases the efficiency of the separation of carriers on p-n junction and leads to an improvement in fill factor current-voltage characteristics. On the other hand, the resulting photocurrent increase with increasing Kc possible losses serial resistances. As the initial value of the series resistance in the studied HPhT does not exceed 1,0 Ohm.cm2 in the investigated range of Kc energy losses in the series resistance does not have a significant impact.
The experimental results showed that with increasing Kc is almost linear increase in temperature p-n junction. Vfr temperature coefficient in the investigated range of illumination changes according to [4], having a negative value changes from -1,8 to -1,96 mV / K, whereas the temperature coefficient Ishc having a positive value, increasing from 2.10-5 to 7.10-5 A / K and depends on the photocurrent spectrum of p-n junction. In samples having a constant strip photosensitivity current Ishc temperature gradient varies little. In HPhT, in the spectral characteristics of the plateau where there is no constant sensitivity is observed a current increase with increasing temperature. With the increase of Kc is a growth temperature coefficient of Ishc. Investigation of the temperature dependence of the efficiency (E) of HPhT shown at temperature T=310K temperature coefficient efficiency (E) is - 0.059 % / K, and at T=345K - 0,025% / K.
Of the maximum output electric power, open circuit voltage, the duty ratio of the CVC and efficiency of lighting levels are given in the Table.
Table
Level of illumination MW/cm2 Maximum electric power MW/cm2 Open-circuit voltage, V Space factor CVC Efficiency, %
88 17,4 0.98 0,72 19.7
264 53,8 1,01 0,71 20,3
440 91,4 1,03 0,71 20,7
688 145,6 1,04 0,70 21,0
880 176,8 1,04 0,68 20,1
PROPERTIES OF GaAs/AlGaAs HETEROPHOTOTRANSFORMATORS WITH HOLOGRAPHIC CONCENTRATORS
Abdukadirov M. A., Azamatov Z. T., Axmedova N. A., Ganiyev A. S., Muminov R. A.
From the experimental data it is seen that Vfr growth is almost over the entire energy range of incident radiation. This indicates that when the data values Kc has not yet achieved the effect of temperature significant p-n transition due to the relatively high temperature stability HPhT [4]. Space factor of CVC preserved without significant change to the level of illumination ~450 MW / cm2, and then there is its decline. Wherein, the efficiency decline occurs since ~ 700 MW / cm2. Decreasing the fill factor and CVC efficiency illuminance range where the short-circuit current varies linearly, obviously due to a change in the parameter CVC recombination p-n junction, which leads to an increase of the saturation current HPhT. The relative change in efficiency with increasing HPhT Kc was ~ 6%, which is in satisfactory agreement with the data [4]. These results confirm that the degree of concentration of Kc =8...9 is actually rational Kc value for operation with a passive heat removal. In general, the experimental data on the properties
of HPhT in the investigated range of the solar flux concentration consistent with the calculated values.
Thus, holographic coating may be used as light flux concentrators in the development of new types of power systems convert solar streams with high light levels.
Список литературы:
1. Lantratov V.M., Kalyuzhny N.A., Mintairov S.A. and others FTP. 2007. т.41. №6. P. 751-755
2. Afyan V.V., Vartanyan A.V. Coll. articles «Solar concentrators for photovoltaic installations» under. ed. V.A.Grilihes. Energoatomizdat. 1986. P. 19-23
3. Muminov R.A., Azamatov Z.T., Akbarov N.A. and others «Geliotexnika». 2014. №3. P. 31-32.
4. Griliches V.A., Orlov P.P., Popov L.B. Solar energy and space travel. Nauka. 1984. 216 p.
