Performance Of Multi-junction Solar Cells Research Articles

Enhancing Multi-Junction Solar Cell Performance: Advanced Predictive Modeling and Cutting-Edge CIGS Integration Techniques

Historically, multi-junction solar cells have evolved to capture a broader spectrum of sunlight, significantly enhancing efficiency beyond conventional solar technologies. In this study, we utilized Silvaco TCAD tools to optimize a five-junction solar cell composed of AlInP, AlGaInP, AlGaInAs, GaInP, GaAs, InGaAs, and Ge, drawing on advancements documented in the literature. Our research focused on optimizing these cells through sophisticated statistical modeling and material innovation, particularly examining the relationship between layer thickness and electrical yield under one sun illumination. Employing III-V tandem solar cells, renowned for their superior efficiency in converting sunlight to electricity, we applied advanced statistical models to a reference solar cell configured with predefined layer thicknesses. Our analysis revealed significant positive correlations between layer thickness and electrical performance, with correlation coefficients (R2 values) impressively ranging from 0.86 to 0.96 across different regions. This detailed statistical insight led to an improvement in overall cell efficiency to 44.2. A key innovation in our approach was replacing the traditional germanium (Ge) substrate with Copper Indium Gallium Selenide (CIGS), known for its adjustable bandgap and superior absorption of long-wavelength photons. This strategic modification not only broadened the absorption spectrum but also elevated the overall cell efficiency to 47%. Additionally, the optimization process involved simulations using predictive profilers and Silvaco Atlas tools, which systematically assessed various configurations for their spectral absorption and current–voltage characteristics, further enhancing the cell’s performance. These findings underscore the critical role of precise material engineering and sophisticated statistical analyses in advancing solar cell technology, setting new efficiency benchmarks, and driving further developments in the field.

Electric Orbit Raising Radiation-Induced Coverglass Darkening and Its Impact on III-V Multijunction Solar Cell Performance

Electric Orbit Raising Radiation-Induced Coverglass Darkening and Its Impact on III-V Multijunction Solar Cell Performance

Enhancement of multijunction solar cell efficiency using a cover layer of Eu3+, Tb3+ and Eu3+/Tb3+ doped GeO2-PbO-Al2O3 glasses as spectral converter of solar radiation

The present study reports the multijunction solar cell efficiency enhancement using a cover layer of GeO2-PbO-Al2O3 glasses single doped with Eu3+ and Tb3+ (with and without Ag nanoparticles (NPs)) and codoped with both of them. We highlight that Al2O3 is a network modifier that promotes the occupation of rare-earth ions in more asymmetric sites, and the change in the coordination environment improves the luminescence that benefits the solar cell efficiency. The influence of the downconversion process and the energy transfer mechanisms between Tb3+ and Eu3+ ions are investigated using different concentrations of Eu2O3 and Tb4O7 in single and codoped samples. Moreover, the plasmonic effects of Ag NPs on the solar cell efficiency increase are also studied and compared with those promoted by different doping concentration to reach the best condition for the multijunction solar cell performance. However, in all cases, it is the contribution of the highest luminescence and considerable transmittance that led to the solar cell best performance. The sample single doped with Eu2O3 promoted an increase of 14%; on the other hand, an increase of 13% was observed for the glass doped with Tb4O7 and with 0.5% of AgNO3. For the case of the codoped samples, solar cell efficiency increase of 10% was reached when the largest Eu2O3 concentration was used.

Effect of Optical–Electrical–Thermal Coupling on the Performance of High-Concentration Multijunction Solar Cells

In the process of high-concentration photovoltaic (HCPV) power generation, multijunction cells work in the conditions of high radiation and high current. Non-uniformity of focusing, the mismatch between the focusing spectrum caused by the dispersion effect and the spectrum of multijunction solar cell design and the increase in cell temperature are the key factors affecting the photoelectric performance of the multijunction solar cell. The coupling effect of three factors on the performance of multijunction solar cell intensifies its negative impact. Based on the previous research, the light intensity and spectral characteristics under Fresnel lens focusing are calculated through the optical model, and the optical–electrical–thermal coupling model under non-uniform illumination is established. The results show that obvious changes exist in the concentration spectrum distribution, energy and non-uniformity along different optical axis positions. These changes lead to serious current mismatch and transverse current in the multijunction solar cell placed near the focal plane which decreases the output power. The lost energy makes the cell temperature highest near the focal plane. In the condition of passive heat dissipation with 500 times geometric concentration ratio, the output power of the solar cell near the focal plane decreases by 35% and the temperature increases by 15%. Therefore, optimizing the placement position of the multijunction cell in the optical axis direction can alleviate the negative effects of optical–electrical–thermal coupling caused by focusing non-uniformity, spectral mismatch and rising cell temperature, and improve the output performance of the cell. This conclusion is verified by the experimental result.

Thermal Load in Thinned Ge-Based Multijunction Space Solar Cells

Low energy photons absorbed in a solar cell can contribute to the heating of the device, which negatively affects performance. This is especially important in germanium, as it presents high free-carrier absorption. Thinning of Ge substrates is a technique which aims to reduce weight and improve performance of multijunction solar cells. Additionally, it presents the opportunity to reflect low energy photons via a rear side infrared reflector. We perform optical simulations and show that thinning an InGaP/GaAs/Ge solar cell from 140 to 40 μm with a gold back reflector can reduce the cooling power requirements by 9.6% for a highly doped substrate, and 7% for a lightly doped one. In terms of temperature, this represents a reduction of 8 °C and 6 °C, respectively.

Subcells Analysis of Thin‐Film Four‐Junction Solar Cells Using Optoelectronic Reciprocity Relation

A thin‐film AlGaInP/AlGaAs/InGaAs/InGaAs inverted metamorphic multijunction solar cell with a bandgap of 1.96/1.53/1.16/0.83 eV is fabricated. The photoelectric conversion efficiency reaches 34.89% with an open‐circuit voltage of 3.54 V under AM1.5 G spectrum. The analysis of individual subcells is the key to evaluating the performance of multijunction solar cells. The current density versus voltage characteristics of four subcells are calculated using optoelectronic reciprocity relation between the external quantum efficiency and the different injection current densities electroluminescence. The analysis of the performance characteristics of four subcells concludes that the key to limiting the overall efficiency improvement is the deep‐level recombination of the AlGaInP top subcell and the bulk recombination of 0.83 eV InGaAs bottom subcell. Targeted optimization of the top subcell and the bottom subcell is expected to significantly improve efficiency.

Designing anti-reflective microlens arrays for space solar cells

In this study, a design for developing an anti-reflective microlens array is presented to increase the performance of multi-junction solar cells for satellite power systems. In line with the findings obtained, it was determined that the designed anti-reflective microlens arrays for space application provided a total increase of 5.9% in the amount of the current generated from solar cells and that the mass of a unit cell was 0.585 g, and it was concluded that they have the potential to be developed in terms of mass and performance for satellite platforms.

Wafer integrated micro‐scale concentrating photovoltaics

AbstractA novel micro‐scale photovoltaic concept, Wafer Integrated Micro‐scale Photovoltaics (WPV), is proposed, analyzed, and experimentally demonstrated. The WPV concept seamlessly integrates multijunction micro‐cells with a multi‐functional silicon platform that simultaneously provides optical concentration, hybrid PV/CPV architecture, and mechanical alignment features. Fabrication and optical performance characterization of the Si platform are described in this paper. Over 100% improvement in the concentration‐acceptance‐angle product (CAP) is demonstrated using the wafer‐embedded micro‐concentrating elements, leading to significantly reduced module material and fabrication costs, sufficient angular tolerance for low‐cost trackers, and an ultra‐compact optical architecture compatible with commercial flat panel infrastructures. The development of a prototypical module with a 400× concentration ratio is described. Outdoor optical characterization of the module shows acceptance angles of ±1.7° and ±2.5° for 90% of on‐axis power and full‐width‐half‐maximum, respectively. The projected performance of the PV/CPV hybrid architecture illustrates its potential for cost‐effective collection of both direct and diffuse sunlight, thereby extending the geographic and market domains for cost‐effective PV system deployment. Leveraging low‐cost micro‐fabrication and high‐level integration techniques, the WPV approach presents a promising route to combine the high performance of multijunction solar cells and the low costs of flat‐plate Si PV systems.

Effect of chromatic aberration on performance of concentrated multi-junction solar cells and their optimization

In order to investigate the influence of the chromatic aberration on the performance of multi-junction solar cells, the performance of the triple-junction GaInP/GaInAs/Ge solar cell under high concentration condition is investigated by a three-dimensional (3D) model based on distributed circuit units. Moreover, the effects of chromatic aberration on the performance of solar cells with different sizes are studied by analyzing the distributions of the voltage, the dark current and the transverse current in each layer. It is indicated that the photo-generated current is mismatched in local region of multi-junction solar cell, which is caused by chromatic aberration. However, the mismatched photo-generated current can be compensated for by the form of transverse current, and the current can be better matched when the size of solar cell is reduced. When the size of solar cell is as big as 20 mm20 mm, the mismatched photo-generated current is large, so are the transverse current and the dark current. But the transverse current is far less than the dark current, only 12% of the mismatched photo-generated carriers can flow from the edge to the center of the cell through the transverse resistance between the sub-cells, the rest of the photo-generated carriers are lost in the form of dark current, and the cell is in a state of current mismatching. Finally, the chromatic aberration gives rise to a reduction in the short-circuit current density, and the efficiency is only 94% as high as that of non-chromatic aberration. When the size of the cell decreases, the mismatched photo-generated current and the transverse current also decrease gradually, but the dark current caused by the chromatic aberration exponentially decreases more quickly, and the ratio of the transverse current to the mismatched photo-generated current increases gradually. Therefore, the overall state of the current mismatching is alleviated, and the short-circuit current density is increased gradually. Moreover, when the size of solar cell is 2 mm2 mm, the transverse current is much larger than the dark current, 99.98% of the mismatched photo-generated carriers can be compensated for in the form of transverse current. Although the photo-generated current of the cell is mismatched in local region, the overall is still in the state of current matching. The short-circuit current densities with and without chromatic aberration are equal, but the filling factor is reduced due to the transverse resistor. When the size of cell is further reduced, the mismatched photo-generated current is very small, and the influence of the transverse series resistance decreases gradually. Therefore, the value of the filling factor gradually approaches to the value without chromatic aberration. Furthermore, the performance of solar cell with and without chromatic aberration is nearly the same when the size of solar cell is as small as 0.4 mm0.4 mm. The efficiencies are both about 34.5% and the effects of chromatic aberration can be ignored.

Multijunction Solar Cell Performance in Mars Orbiter Mission (MOM) conditions

Multijunction Solar Cell Performance in Mars Orbiter Mission (MOM) conditions

Investigation of room-temperature wafer bonded GaInP/GaAs/InGaAsP triple-junction solar cells

We report on the fabrication of III–V compound semiconductor multi-junction solar cells using the room-temperature wafer bonding technique. GaInP/GaAs dual-junction solar cells on GaAs substrate and InGaAsP single junction solar cell on InP substrate were separately grown by all-solid state molecular beam epitaxy (MBE). The two cells were then bonded to a triple-junction solar cell at room-temperature. A conversion efficiency of 30.3% of GaInP/GaAs/InGaAsP wafer-bonded solar cell was obtained at 1-sun condition under the AM1.5G solar simulator. The result suggests that the room-temperature wafer bonding technique and MBE technique have a great potential to improve the performance of multi-junction solar cell.

A differential evolution proposal for estimating the maximum power delivered by CPV modules under real outdoor conditions

Concentrating photovoltaics is an innovative alternative to flat-plate module to produce cost-competitiveness electricity. It is based on the use of optical system of reduced cost which is able to concentrate the solar light on a very small surface (high efficiency solar cell). At present, this technology has a marginal position in photovoltaic market and to take off needs to increase the confidence of the public and private sector. A better understanding of the concentrating photovoltaics technology electrical performance under real meteorological conditions would improve this situation. Because the bankability of a concentrating photovoltaics plant is addressed through the modelling of its energy production, an accurate estimation of the maximum power of the these modules is crucial to achieve it. Accordingly, the commercial evolution of concentrating photovoltaic technology demands prediction models for estimating the maximum power delivered by a concentrating photovoltaic module under real atmospheric conditions. Until now the only established standard method for outdoor power rating of this type of modules (ASTME-2527-09, defined by the American Society for Testing and Materials) does not consider the impact of the direct normal irradiance spectral distribution. The solar spectrum has an important influence on the electric performance of multijunction solar cells which composes concentrating photovoltaic modules.In this work, an analysis of the inclusion in the prediction model of the solar spectrum by means of two indexes (spectral matching ratio and the average photon energy) and different spectral intervals is performed. Then, a differential evolution proposal for the estimation of regression coefficients for the two multivariable regression models is described. The accurate calculation of the model parameters reveals relations among the atmospheric conditions very useful for the experts. The multivariable regression models have been applied to two different concentrating photovoltaic modules, obtaining mean absolute percentage error values within the range 1.91–3.94%. The use of these accurate models for the estimation of the maximum power would allow to estimate the electric production of a concentrating photovoltaic power plant and the analysis of its costs and profitability, with the consequent benefits for the commercial development of this technology.

Practical Limits of Multijunction Solar Cell Performance Enhancement From Radiative Coupling Considering Realistic Spectral Conditions

III-V multijunction solar cells (MJSCs) operate close to the radiative limit under solar concentration. In this regime, radiative losses from the semiconductor material in one junction of the solar cell can be absorbed by a subsequent junction, thereby transferring charge from one subcell to another. Under blue-rich solar spectra, radiative coupling can improve the electrical performance by lifting constraints imposed by a series connection of subcells. We calculate the practical limit of performance enhancement due to the radiative coupling effect for MJSCs under a wide range of atmospheric conditions encountered in potential sites for concentrator photovoltaic systems. Three-junction and four-junction solar cells with current matched and current mismatched designs under the AM1.5D spectrum were considered. Under realistic atmospheric conditions, the relative enhancement to power due to radiative coupling is found to be 1% or less for current-matched triple-junction solar cells. Enhancement of up to 21% can be expected for noncurrent-matched quad-junction devices. The energy yield improvement over an annual period is shown to be up to 5% for the best combinations of devices and sites.

Positioning and doping effects on quantum dot multi-junction solar cell performance

The positioning of InAs quantum dot (QD) layers in a triple-junction GaInP/Ga(In)As/Ge solar cell is studied using numerical modeling techniques. An effective medium is used to describe the absorption characteristics and carrier dynamics in each QD layer. The effects of incorporating 110 layers in the emitter, base layers, as well as between these regions of the middle sub-cell are analyzed with current–voltage characteristics and energy band diagrams. The cell with QDs positioned between the emitter and base demonstrated an efficiency of 31% under 1 sun illumination at room temperature. The performance was then increased to 31.3% by optimizing the QD region doping. Copyright © 2014 John Wiley & Sons, Ltd.

The Dependence of Multijunction Solar Cell Performance on the Number of Quantum Dot Layers

The performance improvements of adding InAs quantum dots (QDs) in the middle subcell of a lattice matched triple-junction InGaP/InGaAs/Ge photovoltaic device are studied using the simulated external quantum efficiency, photocurrent, open circuit voltage, fill factor, and efficiency under standard testing conditions. The QDs and wetting layer are modeled using an effective medium consisting of trap states for the former and low confinement potentials for the latter. Although the efficiency stabilizes for more than 100 layers of QDs for the structure studied, the efficiency achieves an absolute efficiency of 31.1% under one sun illumination for 140 layers of QDs. This corresponds to a relative increase of 1.3% compared with a control structure with no QD layers. The performance of the device depends intricately on the magnitude of the confinement potentials representing the wetting layer.

Modelling of thin-film tandem solar cells

Numerical modelling of thin-film tandem solar cells is investigated using PC-1D program. The program is adapted to simulate the performance of multi-junction solar cells. Cadmium-zinc telluride (Cd0.6Zn0.4Te) is chosen as an absorber layer material for the wide band gap top cell and copper indium diselenide (CuInSe2) is chosen as an absorber layer material for the bottom cell in the whole tandem cell structure. The effects of series resistance, shunt resistance, thickness’ of the absorber layers, doping concentrations of the absorber layers, light concentration and temperature on the performance of tandem thin-film solar cells are carried out. The results indicate that the series resistance has a significant effect on the performance of the top cell compared to its effect on the bottom cell. In addition, under high light concentration conditions, the series resistance has a tremendous effect on deteriorating the cell efficiency compared to low concentration conditions. The results also indicate that the temperature change greatly affects the bottom cell more than the top cell. Finally, doping concentrations and thickness’ of the absorber layers of the top and bottom cells are optimised to achieve high efficiency multi-junction cell.

Numerical Investigation of High-Efficiency InGaN-Based Multijunction Solar Cell

A four-junction InGaN-based multijunction solar cell structure is proposed theoretically. The simulation results show that, with the use of appropriately designed compositional grading layers, the performance of InGaN-based multijunction solar cell can be maintained without the cost in performance degradation caused by the polarization-induced electric field and the potential barriers resulting from the heterointerfaces. After the optimization in thicknesses for current matching, a high conversion efficiency of 46.45% can be achieved under 1000-sun AM1.5D illumination, in which the short-circuit current density, open-circuit voltage, and fill factor are 12.2×103 mA/cm2, 4.18 V, and 0.77, respectively. The simulation results suggest that, in addition to the detrimental effects caused by the built-in electric polarization and potential barriers, the issue of crystalline quality is another critical factor influencing the performance of multijunction solar cells.

Tunnel-Junction-Limited Multijunction Solar Cell Performance Over Concentration

The simulation of tunnel junctions is performed by using nonlocal band-to-band and trap assisted tunneling models that are capable of reproducing the experimental current-voltage characteristics of p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> AlGaAs/ n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> AlGaAs and p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> AlGaAs/ n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> GaAs based devices. These simulated characteristics are then implemented within a lattice matched InGaP/(In)GaAs/Ge multijunction solar cell (MJSC) to assess the performance as a function of tunnel junction layer doping in the regime where the TJ limits the performance of the MJSC. At 500 suns, a 4.6% absolute drop in simulated efficiency is observed for an AlGaAs/GaAs bottom TJ corresponding to a degenerately p-doped layer of 2.5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> compared to a TJ with a doping of 4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . A minimum p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> doping level of 3.3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> is required in order to avoid bottom TJ limitation up to 1000 suns concentration for an n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">++</sup> doping of 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> based on the calibrated models. Furthermore, the effects of the peak and valley current densities are shown to have a strong influence on the efficiency over concentration within the TJ limiting regime.

Theoretical performance of multi-junction solar cells combining III-V and Si materials.

A route to improving the overall efficiency of multi-junction solar cells employing conventional III-V and Si photovoltaic junctions is presented here. A simulation model was developed to consider the performance of several multi-junction solar cell structures in various multi-terminal configurations. For series connected, 2-terminal triple-junction solar cells, incorporating an AlGaAs top junction, a GaAs middle junction and either a Si or InGaAs bottom junction, it was found that the configuration with a Si bottom junction yielded a marginally higher one sun efficiency of 41.5% versus 41.3% for an InGaAs bottom junction. A significant efficiency gain of 1.8% over the two-terminal device can be achieved by providing an additional terminal to the Si bottom junction in a 3-junction mechanically stacked configuration. It is shown that the optimum performance can be achieved by employing a four-junction series-connected mechanically stacked device incorporating a Si subcell between top AlGaAs/GaAs and bottom In0.53Ga0.47As cells.

Demonstration of Photon Coupling in Dual Multiple-Quantum-Well Solar Cells

Multiple-quantum-well (MQW) top cells can enhance the performance of multi-junction solar cells since the absorption edge of top and middle subcells can be tuned with the MQWs to maximize the efficiency. The radiative dominance of MQW top cells can enhance photon coupling, which can potentially reduce the spectral sensitivity of the device and, thus, raise the energy harvest. We present experimental results on photon coupling in dual-junction cells with GaInP top cells containing GaInAsP quantum wells along with theoretical calculation based on a detailed balance model. It is observed that at high concentration, approximately 50% of the dark current of an MQW top cell is transferred to the photocurrent of the cell in the bottom, which is much higher than any previously reported values.