The paper proposes an experimental approach to determine the external quantum efficiency of multijunction solar cells with pronounced optical coupling. A new technique based on the cascade mechanism ...of coupling has been elaborated to separate the influence of the induced luminescent flux from the external illumination and to establish the absolute values of photosensitivity without negative impact of optical interaction between subcells. The novelty of this work lies in the method extended to multijunction devices with N-number of subcells.
•Cascade optical coupling is a feature of multi-junction solar cells.•Optical coupling negatively impacts on quantum efficiency measurements.•Method describes how to avoid influence of optical coupling on experimental data.
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.
Grown by metalorganic vapour phase epitaxy (MOVPE) InxGa1−xAs metamorphic laser power converters have been considered. Metamorphic buffer designs with high quality top layers have been developed. ...Photovoltaic converters with In0.24Ga0.76As photoactive area and optimised buffer have demonstrated efficiency 41.4% for 1064 nm monochromatic radiation conversion and ∼40% for laser power conversion.
GaSb-based thermophotovoltaic converters for a selective mantle-type Y
2
O
3
emitter coated with rare-earth oxides Er
2
O
3
/Yb
2
O
3
are investigated. Matching of the converter spectral response ...with the peak emitter-radiation wavelength λ = 1540 nm provides a thermophotovoltaic conversion efficiency of more than 26% (0.4 W).
An option for the structural design of the metamorphic InGaAs photovoltaic converter is presented. The peculiarity of the proposed device is the ability to operate efficiently with the high-power ...1064 nm laser radiation at the elevated up to +125°C temperatures. The temperature dependencies of the output photovoltaic parameters for two types of InxGa1-xAs laser-power converters are presented in regard to In content: with x = 0.23 and x = 0.18 and with an efficiency of ∼50% and ∼40% (25 °C), respectively. For In0.18Ga0.82As device, an increase in efficiency of up to 50% is recorded upon transition to a temperature range of 50÷60 °C with maintaining efficiency at a level of more than 45% at elevated to 100 °C operating temperatures. In comparison, the "standard" In0.23Ga0.77As device performs a negative efficiency trend within a whole temperature range with absolute values below 45% in practically important operating modes of +75÷100 °C.
Spectroscopic reflectometry was used within 700-1600 nm wavelength range to investigate dispersion curves for In
Al
As, In
Al
Ga
As, and In
Ga
As layers, which constituted the purpose-made ...metamorphic InAlGaAs/GaAs Bragg reflector (BR). The procedure for determining the refractive index based on analyzing variations in cross-correlation coefficient obtained for reflection coefficient calculated and experimental dependences is presented. The sensitivity of the proposed method for variations in refractive index was investigated depending on the number of BR periods, the extinction coefficient of the layers of BR, and the wavelength range with respect to the main reflection maximum.
The effect of positioning of the In
0.8
Ga
0.2
As 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.
The current–voltage characteristics of In
x
Ga
1 –
x
As/GaAs metamorphic photovoltaic converters with built-in
n
-InGaAs/InAlAs Bragg reflectors are studied at an indium content of
x
= 0
.
025–0
.
...24. The series resistance of the heterostructures is measured in the temperature range from 90 to 400 K. It is found that a sharp rise in the resistance of silicon-doped reflectors with an increasing fraction of In is due to weak activation of the donor impurity in InAlAs–
n
:Si layers. As a result, the energy barriers for majority carriers are formed in the latter, with a height of 0
.
32–0
.
36 eV and a substantial width. To suppress this effect, the technology of the Te doping of
n
-InGaAs/InAlAs Bragg reflectors is developed, which reduces the series resistance by five orders of magnitude. This makes it possible to keep the fill factor of the current–voltage characteristic above 80% up to current densities of 2 A/cm
2
. Values exceeding 85%, achieved for the quantum efficiency, indicate that the “memory” and tellurium segregation effects characteristic of this kind of impurity are suppressed.
Abstract
In the work, the effect of In
0.8
Ga
0.2
As quantum dots position in the i-region of a GaAs solar cell on its spectral and photoelectric characteristics has been investigated. Three solar ...cell structures were obtained by metal-organic vapor-phase epitaxy, in which layers of quantum dots were placed in the middle of the i-region and also have been shifted to the base and the emitter. As a result, it has been shown that the solar cell with a quantum dot array shifted to the base demonstrates the smallest open-circuit voltage drop and, accordingly, a higher efficiency value.
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