Triple-junction Cells Research Articles

Concentrating characteristics of Fresnel lens with prism secondary concentrator and optimization of high concentrating photovoltaic module with triple-junction cell

At present, Fresnel lens is commonly used as a concentrator in high concentrating photovoltaic (HCPV) module, and the triple-junction cell is currently one of the most common multi-junction cells used in it. The triple-junction cell is composed of three p-n junctions in series. Each sub-cell in it absorbs different-wavelength light. The solar cell efficiency of Ⅲ-V multi-junction high concentrating photovoltaic increases up to 46%, which the corresponding module efficiency is quite different from. The output power of the solar cell is related to not only the illumination energy, but also the spectral distribution and the uniformity of the illumination. The loss caused by the non-ideal concentration of the concentrator in the module is as high as 20%. After sunlight enters the lens, the direction of transmission of a monochromatic light is different, because a lens has different refractive index for different-frequency light. So the light disperses when leaving the lens, and thus the colors are arranged in a certain order to form a spectrum. Owing to the dispersion and the differences in refractive index among different spectral bands, the illumination distributions of the three spectral bands are different and non-uniform on the focal plane of lens. The divergence of light will obviously weaken the non-uniformity of the illumination on the solar cell surface. So the divergence angle of the light source has a greater influence on the cell performance because the non-uniformity of illumination has a negative influence on the performance of the cell.In this paper, according to the establishment of optical model and three-dimensional cell circuit network model under non-uniform illumination, taking Ⅲ-V triple-junction cells for example, we study the concentrating characteristics and photovoltaic characteristics of HCPV module with Fresnel lens concentrator and prism secondary concentrator. The results show that due to the non-parallel incident light and dispersion of the Fresnel lens, the concentrating spots of short-wave light, medium-wave light and long-wave light are divergent and their illuminations are non-uniform, resulting in the spectral response mismatch loss of the three sub-cells in the triple-junction cell, and the photovoltaic performance of the HCPV module also declines. The results show that the secondary optics element is obviously effective in reducing the non-uniformity of the illumination and the temperature which the Fresnel lens creates. However, each waveband of light has a different spot size at the same position, similar to the Fresnel lens without the secondary optics element. So the varieties of cell performance at different positions are similar too. And, by optimizing the focusing characteristics of the three wave bands along the optical axis, the power output of the HCPV module can increase more than 10%. The simulation results are verified experimentally.

Experimental characterization and multi-physics simulation of a triple-junction cell in a novel hybrid III:V concentrator photovoltaic–thermoelectric receiver design with secondary optical element

A lattice-matched monolithic triple-junction Concentrator Photovoltaic cell (InGa(0.495)P/GaIn(0.012)As/Ge) was electrically and thermally interfaced to a Thermoelectric Peltier module. A single optical design secondary lens was bonded to the CPV-TE receiver. The hybrid SILO-CPV-TE solar energy harvesting device was electrically, thermally and theoretically investigated. The electrical performance data for the cell under variable irradiance and cell temperature conditions were measured using the integrated thermoelectric module as both a temperature sensor and as a solid-state heat pump. The cell was electrically characterised under standard test conditions (1000 W/m2 irradiance, 25°C temperature and AM1.5G spectrum) for comparison with literature data. Transient multiphysics simulations in ANSYS CFX 15.0 were carried out to calculate cell temperatures and to determine the short circuit current and temperature coefficient in a scaling law. The optimization was used to determine 15 model parameters for the component sub-cells within the triple-junction cell at STC with a MATLAB scaling law. The root-mean-square error in electrical currents between measurement and simulations was 0.66%.

Impact of solar cell characteristics and operating conditions on the sizing of a solar powered nonrigid airship

Non-rigid airships (blimps) use buoyant gas to counter their weight, and modern designs also incorporate solar panels and rechargeable batteries for propulsion. Combining these concepts offers the potential for indefinite flight duration, thus rendering blimps suitable for surveillance missions where station and altitude are maintained. However, a consistent analysis of the impact of solar cell characteristics, wind speeds and irradiance on the airship size is not available. Therefore, this work aims to study the effect of varying solar cell efficiency and weight, energy storage system specific energy, wind speed and solar irradiance on a solar powered airship's length, mass and solar coverage area. It is demonstrated that single-junction and triple-junction cells consistently lead to similar airship sizes and masses despite large differences in efficiency and weight. The use of thin-film cells, while competitive at wind speeds below 14 m/s, on the other hand, leads to a significantly greater mass and size at higher wind speeds. The specific energy of the storage system has a strong impact on length and mass, while cell coverage is unaffected. However, for energy densities above 1000 Wh/kg gains become small. Airship size is larger at higher altitudes, and solar irradiance is greater, which yields an airship with a significantly smaller solar cell area and thus lower mass. Sufficient propulsive power to overcome drag is unavailable where solar irradiance is low and wind speeds are high, although solar cell efficiency is also a contributing factor, and blimps employing higher efficiency cells can operate over a wider range in speed and irradiance. High speeds and low irradiance necessitate a large blimp size, weight and solar coverage, with speed affecting length and mass more acutely than irradiance, while both speed and irradiance affect solar cell proportion nearly equally.

Key Points in the Latest Developments of High‐Efficiency Thin‐Film Silicon Solar Cells

Thin‐film silicon has been intensively used in photovoltaic applications. In recent years, most of the record efficiencies in thin‐film silicon solar cells have been updated frequently, particularly in microcrystalline silicon solar cells. In this article, key points in the latest developments of high‐efficiency thin‐film silicon solar cells are reviewed with a short overview of thin‐film silicon technology. The main driver for the efficiency improvement of microcrystalline silicon cells was the development of sophisticated light scattering substrates. The well‐designed honeycomb‐textured substrates enabled a systematic and detailed optimization to realize the growth of high‐quality films and significant light absorption enhancement simultaneously. The knowledge obtained about microcrystalline silicon solar cells and the insights regarding light‐induced degradation of a‐Si:H solar cells were successfully transferred to triple junction cells, which was demonstrated by the achievement of the record stabilized efficiency of 14%.

GaSb‐Based Solar Cells for Full Solar Spectrum Energy Harvesting

AbstractIn this work, a multijunction solar cell is developed on a GaSb substrate that can efficiently convert the long‐wavelength photons typically lost in a multijunction solar cell into electricity. A combination of modeling and experimental device development is used to optimize the performance of a dual junction GaSb/InGaAsSb concentrator solar cell. Using transfer printing, a commercially available GaAs‐based triple junction cell is stacked mechanically with the GaSb‐based materials to create a four‐terminal, five junction cell with a spectral response range covering the region containing >99% of the available direct‐beam power from the Sun reaching the surface of the Earth. The cell is assembled in a mini‐module with a geometric concentration ratio of 744 suns on a two‐axis tracking system and demonstrated a combined module efficiency of 41.2%, measured outdoors in Durham, NC. Taking into account the measured transmission of the optics gives an implied cell efficiency of 44.5%.

A 6-focus high-concentration photovoltaic-thermal dish system

Abstract We present the design, optical characterization and full-system modeling of a novel 6-focus, high-concentration photovoltaic-thermal solar polygeneration system, aiming at an energy-efficient and cost-effective utilization of the solar resource. Essential to this system is a compact, modular solar dish concentrator design optimized for mass-production, structural rigidity, and scalability, with a high geometric concentration ratio of 1733× at each of its six receivers. Every receiver comprises 36 triple-junction CPV cells, interconnected in a unique hybrid parallel-serial scheme that mitigates mismatch losses caused by non-uniform irradiance distributions. Cogeneration is enabled by using high-performance microchannel heat exchangers, allowing the extraction of low grade heat for secondary thermal processes. The tested prototype achieves an average solar radiative flux of 1374 suns on each of the receivers. By optimizing several design parameters, the CPV-thermal system can deliver a solar-to-electricity conversion efficiency of 28.5% in PV-only mode and 26.6% in cogeneration mode while extracting heat at 89.8 °C, and a power of 12.1 kW el and 11.3 kW el /21.5 kW th respectively, matching the performance of state of the art CPV commercial systems, while striving towards a reduction of the investment costs.

High-efficiency III–V//Si tandem solar cells enabled by the Pd nanoparticle array-mediated “smart stack” approach

Smart stack is a handy technique to produce two-terminal tandem structures from various photovoltaic materials using Pd nanoparticle arrays as bonding mediators. Because of the increasing interest in III–V/Si integration, we herein demonstrated smart stack-based triple-junction cells consisting of InGaP/GaAs and crystalline Si subcells. Despite the use of classic Al-back surface field-type Si subcells, current matching with the InGaP/GaAs subcells was realized, and the promising efficiency of 25.1% was successfully achieved. The potential and versatility of the smart stack approach as a fabrication tool for high-efficiency multi-junction cells were further enhanced through this study.

Origin of the Degradation of Triple Junction Solar Cells at low Temperature

The degradation of solar cells under irradiation by high energy particles (electrons, protons) is the consequence of the introduction of defects trapping minority carriers, which are then not collected by the junction. However, at low temperature, defects located in the space charge region can also induce a tunneling current that results in an apparent decreases of the maximum power. The degradation produced by this tunneling current can depend on temperature, since the concentration of defects created by an irradiation is usually temperature dependent, and can be larger than the degradation associated with carrier recombination. For instance, as we shall see below, an irradiation with 1 MeV electrons at 120 K with a fluence of 3.0 × 10 15 /cm 2 induces a decrease of less than 10 % in the short-circuit current (I sc ) and open-circuit voltage (V oc ) of triple junction (TJ) cells, but a decrease of about 40 % in the maximum power (P max ), which implies that more than half of the total degradation of P max should be assigned to another loss mechanism, tunneling in this case. In this work, we demonstrate that this additional degradation must indeed be ascribed to a tunneling process and we investigate the variation of the tunneling current versus fluence induced by electron irradiation in TJ cells, in order to tentatively ascribe the tunneling components to specific sub-cells.

Metal Matrix Composite Solar Cell Metallization

Advanced solar cells are moving to ever thinner formats in order to save mass and in some cases improve performance. As cells are thinned, the possibility that they may fracture or cleave due to mechanical stresses is increased. Fractures of the cell can degrade the overall device performance if the fracture propagates through the contact metallization, which frequently occurs. To address this problem, a novel semiconductor metallization system based on multi-walled carbon nanotube (CNT) reinforcement, termed metal matrix composite (MMC) metallization is under investigation. Electro-mechanical characterization of MMC films demonstrate their ability to provide electrical conductivity over >40 micron wide cracks in the underlying semiconductor, with the carbon nanotubes bridging the gap. In addition, these materials show a “self-healing” behaviour, electrically reconnecting at ~30 microns when strained past failure. Triple junction (TJ) space cells with MMC metallization demonstrated no loss in J sc after intentional fracture, whereas TJ cells with conventional metallization suffer up to 50% J sc loss.

Advances in Dilute Nitride Multi-Junction Solar Cells for Space Power Applications

A sub-cell with bandgap of around 1 eV is required to improve the efficiency of multi-junction solar cells beyond what is possible with legacy triple-junction architectures [1]. Solar Junction Corporation has been focused since 2007 on the development and commercialization of dilute nitride materials to be used as the 1eV sub-cell in a fully lattice matched multijunction solar cell. Initial focus on the terrestrial concentrating photovoltaics (CPV) market led to Solar Junction Corp.’s achievement of multiple world records in multi-junction solar cell efficiency with its triplejunction cells on GaAs [2], [3]. These solar cells have been available as commercial products since 2010. Solar Junction Corp. has leveraged its high-quality, manufacturable dilute nitride material to develop and introduce an entirely new class of space solar cells capable of reaching over 33% AM0 conversion efficiency in a four-junction (4J) configuration lattice matched to active Ge substrates, with a clear line of sight to 36% AM0 efficiency in five- or six-junction devices that can be manufactured more cost-effectively than devices relying on metamorphic technologies.

连续激光对三结GaAs电池的损伤效应

连续激光对三结GaAs电池的损伤效应

The Global Precipitation Measurement (GPM) Spacecraft Power System Design and Orbital Performance

The Global Precipitation Measurement (GPM) spacecraft was jointly developed by National Aeronautics and Space Administration (NASA) and Japan Aerospace Exploration Agency (JAXA). It is a Low Earth Orbit (LEO) spacecraft launched on February 27, 2014. The spacecraft is in a circular 400 Km altitude, 65 degrees inclination nadir pointing orbit with a three year basic mission life. The solar array consists of two sun tracking wings with cable wraps. The panels are populated with triple junction cells of nominal 29.5% efficiency. One axis is canted by 52 degrees to provide power to the spacecraft at high beta angles. The power system is a Direct Energy Transfer (DET) system designed to support 1950 Watts orbit average power. The batteries use SONY 18650HC cells and consist of three 8s x 84p batteries operated in parallel as a single battery. The paper describes the power system design details, its performance to date and the lithium ion battery model that was developed for use in the energy balance analysis and is being used to predict the on-orbit health of the battery.

Monolithic Two-Terminal III–V//Si Triple-Junction Solar Cells With 30.2% Efficiency Under 1-Sun AM1.5g

Stacking III–V p-n junctions on top of wafer-based silicon solar cells is a promising way to go beyond the silicon single-junction efficiency limit. In this study, triple-junction GaInP/Al x Ga 1- x As//Si solar cells were fabricated using surface-activated direct wafer bonding. Metal–organic-vapor-phase-epitaxy-grown GaInP/Al x Ga1- x As top cells are bonded at low temperature to independently prepared wafer-based silicon cells. n-Si//n-GaAs interfaces were investigated and achieved bulk-like bond strength, high transparency, and conductivity homogeneously over 4-inch wafer area. We used transfer-matrix optical modeling to identify the best design options to reach current-matched two-terminal devices with different mid-cell bandgaps (1.42, 1.47, and 1.52 eV). Solar cells were fabricated accordingly and calibrated under AM1.5g 1-sun conditions. An improved Si back-side passivation process is presented, leading to a current density of 12.4 mA/cm2 (AM1.5g), measured for a flat Si cell below GaAs. The best 4 cm2 GaInP/GaAs//Si triple-junction cell reaches 30.2% 1-sun efficiency.

Wafer Surface Tuning for a-Si:H/μc-Si:H/c-Si Triple Junction Solar Cells for Application in Water Splitting

Abstract Amorphous/microcrystalline/crystalline silicon (a-Si:H/μc-Si:H/c-Si) triple junction solar cells have been developed to directly split water, for which operating voltages (Voc) >1.5 V (depending on the catalysts) are needed. These cells are an inexpensive alternative to high efficiency, high voltage multi junction solar cells based on scarce elements like III-V semiconductors. To obtain a dense μc-Si:H middle cell with high Voc, we investigated a second acid-based polishing step to systematically smoothen the sharp V-shaped valleys present after standard KOH pyramid texturing. This way, we reduced defective regions in the 2 – 3 μm thick μc-Si:H middle and the 250 – 300 nm thick a-Si:H top cell. Quantitatively analyzing the surfaces by atomic force microscopy, we found that a reduction from 49° to 25° in the maximum of the angle distribution of the surface allowed an increase in Voc of >130 mV and an increase in fill factor (FF) from ∼50% to >70%. By further optimizing the nanocrystalline silicon oxide (nc-SiOx:H) intermediate reflector layer placed between bottom and middle cell, the nc-SiOx:H top cell p-layer as well as middle cell thickness, we could increase the solar to electricity conversion efficiency to 12.7%. Very promising first results are presented by utilizing the triple junction cell for stand-alone water splitting device in alkaline electrolysis as demonstrated by using a standard 3-electrode setup.

Stabilized 14.0%-efficient triple-junction thin-film silicon solar cell

We report on a high-efficiency triple-junction thin-film silicon solar cell fabricated using the substrate configuration. An undoped hydrogenated amorphous silicon (a-Si:H) solar cell grown using triode plasma-enhanced chemical vapor deposition, which is more stable against light soaking, was applied to the a-Si:H/μc-Si:H/μc-Si:H triple-junction cells with honeycomb-textured substrates. To find the best balance in short circuit density and fill factor, we quantitatively investigated the effect of current mismatch on triple-junction cells. Accordingly, a stabilized efficiency of 14.04% was achieved in an a-Si:H/μc-Si:H/μc-Si:H triple-junction solar cell with a minimum light-induced degradation of 4%, setting a new record in this type of solar cells.

Photovoltaic characteristics of each subcell evaluated in situ in a triple-junction solar cell

New manufacturing processes were proposed to evaluate important photovoltaic properties of each subcell in an InGaP/InGaAs/Ge triple-junction solar cell. In addition to the triple-junction cell, an InGaAs/Ge double-junction cell and a Ge single-junction cell were also fabricated and employed for evaluation. The key merit of the double-junction cell is that semiconductor layers of forming InGaP top subcell are retained as a dummy top subcell. Thus, the InGaAs middle subcells in both triple- and double-junction cells will receive the same light spectrum. Similarly, the Ge single-junction cell is fabricated with dummy top and middle subcells as light filters. Open-circuit voltage, short-circuit current, conversion efficiency, and current mismatched ratio were measured for evaluating and optimizing each subcell. It is found that Open-circuit voltages are 1.295, 0.967, and 0.212Vfor the InGaP, InGaAs, and Ge subcells with temperature coefficients of −2.5, −1.99, and −1.87mV/°C. Thus the Ge subcell no longer acts a real solar cell at temperature over ∼140°C. Besides, effect of ambient temperature on short circuit currents of all as-fabricated solar cells is not relevant. The current mismatched ratios are 18.6–20% at temperature ranged from 25°C to 80°C. A low efficiency of ∼18.7% is due partly to the poor current match. However, the processing concept proposed is useful as a method of matching currents among the subcells.

Very thin and stable thin-film silicon alloy triple junction solar cells by hot wire chemical vapor deposition

We present a silicon-based triple junction solar cell that requires a deposition time of less than 15 min for all photoactive layers. As a low-bandgap material, we used thin layers of hydrogenated amorphous silicon germanium with lower band gap than commonly used, which is possible due to the application of hot wire chemical vapor deposition. The triple junction cell shows an initial energy conversion efficiency exceeding 10%, and with a relative performance stability within 6%, the cell shows a high tolerance to light-induced degradation. With these results, we help to demonstrate that hot wire chemical vapor deposition is a viable deposition method for the fabrication of low-cost solar cells.

Demonstrating Dilute-Tin Alloy SiGeSn for Use in Multijunction Photovoltaics: Single- and Multijunction Solar Cells With a 1.0-eV SiGeSn Junction

SiGeSn ternary alloys offer a means to fabricate a 1.0-eV subcell junction for inclusion in a multijunction solar cell. The main advantage of the SiGeSn alloy is a tuneable bandgap energy and variable lattice parameter, enabling the material to be integrated into the existing lattice-matched multijunction architectures. Recent growth, structural, optical, and device results from SiGeSn material, with energy gaps in the vicinity of 1.0 eV and lattice matched to Ge substrates, are presented. An all lattice-matched InGaP/InGaAs/SiGeSn triple-junction cell is presented and compared with a conventional InGaP/InGaAs/Ge solar cell. Comparable short-circuit current values of 13.9 mA/cm2 are obtained for both devices under the AM1.5G spectrum, whereas the open-circuit voltage and fill factor are reduced in the device with the SiGeSn subcell. Peak external quantum efficiency in the SiGeSn single junction in excess of 80% is realized, placing a lower limit on the base minority hole diffusion length of 5 $\mu$ m with surface recombination velocities in close agreement to those found in bulk Ge material.

Modelling and simulation of single- and triple-junction solar cells using MATLAB/SIMULINK

The main objective of this paper is to determine the single- and triple-junction solar cells’ I–V and P–V curves, define maximum voltage, current, and power. The paper demonstrates and analyses different environmental conditions that affect the solar cells, such as temperature and irradiance. The performance of single- and triple-junction solar cells is evaluated by analysing the fill factor. In this work, the analysis of single- and triple-junction solar cells is carried out through software simulation. Different conditions demonstrated to observe the results of this variation in both single- and triple-junction cells, such as observing the solar cell behaviour under variation of temperature between 15°C (288.315 K) and 45°C (318.15 K) for the single-junction cell and between 268.15 K (−5°C) and 348.15 K (75°C) for the triple-junction cell to observe the effect of temperature on open circuit voltage, the variation of different levels of irradiance to observe its effect on open circuit voltage and current density on both cell types, and cell performance evaluation using the fill factor concept. Practical results used in this paper are obtained from Clyde Space’s laboratories. Tests of Clyde Space were done using halide lamps to simulate the irradiation conditions with irradiance of half sun which is equivalent to 0.05 W cm−2. The operation was done under temperature of 40°C which is equivalent to 313.15 K.

Field Investigation of the Effect of Spectral Response Upon Photovoltaic Energy Yields

The operating efficiencies of multijunction photovoltaic (PV) cells are sensitive to changes in the spectral distribution of solar irradiance. Previous studies suggest that optimizing a cell's spectral response can improve energy yields. To examine how this affects their performance in the field, two sets of triple-junction photovoltaic cells with different spectral responses are being characterized side-by-side outdoors in Nicosia, Cyprus. High-resolution measurements of the solar spectrum are also being recorded at this location, allowing a detailed examination of the cell performances under varying spectral conditions. Using spectral matching ratios to analyze the data has indicated that daily changes in the fill factors of the cells can be attributed to their spectral responses. However, average performance ratios over the period of testing are similar for the two cell types. An in-depth analysis reveals that this is due to a combination of both the spectral responses and the spectral resource at the test site, where both cells operate close to their optimum. This indicates that customizing the spectral response of a cell may only be advantageous for applications under an extreme spectral resource distribution.