GaAs Solar Cells Research Articles

21.2% GaAs Solar Cell Using Bilayer Electron Selective Contact

GaAs remains one of the crucial materials for solar cell applications as it boasts the world's highest efficiency single‐junction solar cells. However, their high cost limits their widespread terrestrial applications. Traditional GaAs solar cells require a complex stack of doped junctions, which can only be grown using epitaxy, which is a very costly technique. Herein, a nonepitaxial bilayer of ZnO and TiO2 as electron‐selective contact is studied. It is shown that a bilayer selective contact can achieve very high performance through interface band engineering and a reduction of the barrier for electron transfer. 21.2% efficient solar cells is achieved, with Voc of 1.04 V, Jsc of 26.13 mA cm−2, and a fill factor of 77.8%. The Voc reported in the article is comparable to the highest Voc reported for substrate‐based GaAs solar cells of 1.075 V. An experimental loss analysis shows that the device is mainly limited by series and shunt resistance and reflection losses, both of which can further be minimized by optimization of the fabrication process. The results presented will be very useful for the further development of cheaper GaAs solar cells, whereas the bilayer selective contact concept can be implemented for other kinds of solar cells.

Optical design of ultra-thin GaAs solar cells based on trapezoidal pyramid structure

This study analyzed the solar absorption characteristics of Trapezoidal Pyramid ultra-thin GaAs solar cells (GTCs) using the finite difference time domain (FDTD) method. The study explored the influence of geometric parameters of trapezoidal pyramid structures (TPs) in GTCs, including different heights and up/down ratios, on the photoelectric characteristics of GTCs. Ultra-thin GaAs solar cells containing TPs exhibited an optical absorption rate exceeding 90 % under the AM1.5 solar spectrum (300–1100 nm), with an average of 95.55 %. The short-circuit current density (Jsc), open-circuit voltage (Voc), and maximum power (Pmax) were calculated using DEVICE software, and the geometric structure of GTCs was optimized based on the maximum value of Jsc. The electrical simulation results show that the maximum Jsc was 33.83mA/cm2. The Jsc of GTCs was 30.97 % higher than that of Ultra-thin GaAs solar cells without TPs (planar GACs), resulting in a PCE of 24.34 %. These findings demonstrate that the TPs array has a strong optical capture effect and highlight the significant potential of GTCs in solar absorption. This work provides valuable insights for the structural design of GaAs solar cells and suggests that further exploration will lead to even greater improvements in the PCE of GaAs solar cells.

Refining DIIS algorithms for Si and GaAs solar cells: incorporation of weight regularization, conjugate gradient, and reverse automatic differentiation techniques.

Pivotal enhancements in electronic minimization algorithms, which are vital for the advancement of computational materials science, are introduced in this research. Our research is dedicated to refining the DIIS algorithm specifically for electronic structure calculations of silicon (Si) and gallium arsenide (GaAs) solar cells, aiming to enhance their efficiency and stability. We have enriched DIIS by integrating a weight regularization factor, significantly bolstering its convergence stability. This modification enhances iteration robustness and curtails the average iteration duration, thus streamlining the convergence process. Furthermore, we have incorporated the conjugate gradient (CG) algorithm to proficiently resolve symmetric positive definite residual matrices. This inclusion substantially accelerates the solution-finding process within the DIIS framework. A novel aspect of our research is the application of reverse automatic differentiation (AD), deployed in two distinct methodologies: the construction of the Jacobian matrix and direct chain rule application for gradient computation. These approaches involve sophisticated mathematical techniques that enhance computational precision and efficiency specifically for Si and GaAs solar cell materials in determining the optimal weights for residual combinations during DIIS iterations. The integration of these advanced methods into the DIIS algorithm not only augments its convergence stability but also ensures a substantial reduction in total computational time. Our findings demonstrate that the enhanced DIIS, CG-enhanced DIIS, and AD-integrated DIIS methods collectively lead to a more efficient electronic minimization process. This balance of stability and efficiency is crucial in high-performance computational materials science, particularly for complex systems analysis. The findings of this research represent a notable advancement in computational strategies for Si and GaAs solar cell materials, providing enhanced methodologies and insights that significantly improve the efficiency and stability of electronic structure calculations in these critical components of renewable energy technologies.

High‐Efficiency GaAs Solar Cells Grown on Porous Germanium Substrate with PEELER Technology

High‐Efficiency GaAs Solar Cells Grown on Porous Germanium Substrate with PEELER Technology

Improvement of radiation resistance of GaInP/GaInAs/Ge triple-junction solar cell with GaInAs/GaAsP quantum wells

Introducing quantum wells (QWs) into a GaAs solar cell can expand its spectral response range to raise the short-circuit current (J sc). GaInP/GaInAs/Ge triple-junction (TJ) solar cells with strain-balanced InGaAs/GaAsP QWs in a GaInAs cell have been fabricated and irradiated by 1 MeV electron fluences. The AM0 efficiency of the TJ cell increases from 30% to 32% by inserting 30 period QWs. Under the electron irradiation condition of 1 MeV, 1 × 1015 cm−2, the radiation resistance of quantum well solar cells (QWSCs) is worse than that of the reference cell without QWs. The effect of QW doping on the radiation resistance of the 30 QWSC has been studied. After irradiation, the radiation resistance of J sc is improved by the unintentional doping of QWs, resulting in lower degradation of efficiency. An efficiency of 26.30% after irradiation is attained and this indicates that the QWSC has expectable potential to be applied to satellites.

Multilayer anti-reflective coating with ultra-low refractive index SiO2 nanopillars for high efficiency multi-junction GaAs solar cells

The anti-reflective coating (ARC) is an essential component in inverted metamorphic triple-junction gallium arsenide (GaAs) solar cells (IMM-SCs) to improve the light absorption and efficiency. The common approach to realize AR function is to construct a multilayer thin-film with a gradient refractive index (n) change from air to the solar cell. In this study, SiO2 nanopillars (SiO2-NPs) are implemented as the top layer in multilayer thin-films to enhance their broadband anti-reflection capability. The transfer matrix method and electron beam (oblique angle) deposition process are applied for the design and fabrication of the multilayer thin-films, respectively. By optimizing the thickness and n of SiO2-NPs thin-films, an IMM-SC with a SiO2-NPs/Al2O3/TiO2 ARC is achieved with an average reflectivity as low as 5.506% in the 300–1300 nm range. The proposed ARCs have significant implications for the window layer designs of high-performance multi-junction solar cells.

Comparative study of parallel gap resistance welding joints between different interconnected foils and GaAs solar cells: Microstructure and thermal reliability

Deployed in space orbits, solar cell arrays are subjected to daunting challenges posed by exceedingly harsh thermal environments. During their operational lifespan in space, potential failures at the joints between solar cells and interconnecting strips can adversely affect the longevity of solar cell arrays. To enhance the thermal reliability of solar cell joints in intricate space conditions, this study delved into the influence of thermal cycle on mechanical properties and microstructures of parallel gap resistance welding (PGRW) joints utilizing both silver (Ag) and Ag-plated Kovar foils. Operating at respective current densities of 410 A/mm2 and 420 A/mm2, these two types of foils exhibit solid-phase interfaces characterized by elemental diffusion. Interface of the joint of Ag foil experiences microscopic deformation and accumulated strain during the thermal cycle, with cracks initiating and propagating at the edges of joint interface. With an escalation in the number of thermal cycles, tensile-shear performance deteriorates, and the fracture morphology shifts from a ductile fracture with evident dimples to a deformation-intensive fracture attributed to thermal fatigue, draped in Ag grains. Conversely, the joints of Ag-plated Kovar foil demonstrate minimal alterations in mechanical properties, microstructures, and fracture morphology due to thermal cycling. This phenomenon reflects noteworthy thermal reliability spanning from −160 °C to 120 °C. The investigation into PGRW joints of Ag-plated Kovar foil holds significant implications for satisfying the high-reliability of solar cell arrays in hostile space environments.

Surface Photovoltage Method for Photovoltaic Quality Control of GaAs-Based Solar Cells

In this paper, we demonstrate the potential of the contactless surface photovoltage (SPV) method for fast and reliable control of GaAs-based solar cells directly on epitaxial heterostructures before metallization and photolithography processes. The magnitude of the SPV corresponds to the generated photovoltage in the photoactive region, which is related to the open circuit voltage of the cell. The focus of this investigation is the potential of dilute nitride compounds grown by low-temperature liquid-phase epitaxy (LPE) for application as intermediate cells in multijunction solar cells. First, SPV spectroscopy is used to determine the photosensitivity spectral range and bandgap of the grown dilute nitride compound layers. Further, the photovoltaic quality of the grown solar cell heterostructures is evaluated by comparing the magnitude of their SPV signals with that of a reference GaAs solar cell. A drastic reduction in the measured SPV is observed for nitrogen-containing solar cell structures, which correlates with the lowering of solar cell open-circuit voltage values measured under standard test conditions. Finally, solar cell structures based on nitrogen-free GaAsSb compounds with the same long-wavelength photosensitivity limit as GaAsSbN are grown by LPE. They show one order of magnitude higher SPV signal and, therefore, have a great potential for solar cell application.

24% Single‐Junction GaAs Solar Cell Grown Directly on Growth‐Planarized Facets Using Hydride Vapor Phase Epitaxy

AbstractA 24%‐efficient single‐junction GaAs solar cell grown directly on a faceted, spalled (100) GaAs substrate after in situ planarization growth by hydride vapor phase epitaxy (HVPE) is achieved. Controlled spalling, a promising low‐cost substrate reuse technique, produces large facets in (100)‐oriented GaAs substrates due to the orientation of the fracture planes used for lift‐off. Planarization by HVPE offers a path toward direct use of these spalled substrates without costly polishing steps. Here, the growth rate anisotropy enabling planarization arising from diffusion and differences in the adsorption of growth species on {n11}B‐type facets relative to (100) is determined. Consecutive planarization and device growth that results in a solar cell with a minimal performance difference relative to a control cell grown on an epitaxy‐ready substrate are demonstrated. These results show that controlled spalling coupled with HVPE planarization is a viable pathway for lowering the cost of III‐V photovoltaics.

Investigation of the Photoelectric Characteristics of GaAs Solar Cells with Different InGaAs Quantum Dot Array Positioning in the i-Region

Investigation of the Photoelectric Characteristics of GaAs Solar Cells with Different InGaAs Quantum Dot Array Positioning in the i-Region

Current Enhancement of Ultrathin GaAs Solar Cells with Rear Light Scattering Structures Using Block Copolymers

Ultrathin GaAs solar cells have gained attention because they are cost‐effective and exhibit high carrier‐collection efficiency and open‐circuit voltage compared with cells with thicker absorber layers. However, ultrathin GaAs solar cells have a low current density due to their thin light‐absorbing layers. To improve the photoabsorption of ultrathin GaAs solar cells, light‐trapping structures with textured front or rear surfaces are necessary, and easy methods for fabricating textured structures are required. In this study, a new method to create light‐scattering textured surfaces using block copolymers is developed. This method only requires spin coating, annealing, and wet etching, making it easily applicable to large‐area devices such as solar cells. An ultrathin GaAs solar cell is fabricated with a rear‐textured structure using block copolymers as masks for wet etching. The results demonstrate that the short‐circuit current density is enhanced by 1.39 mA cm−2, which improves the energy conversion efficiency by 0.71 percentage points compared with a reference cell without a rear‐textured structure.

High‐Efficiency GaAs Solar Cells Grown on Porous Germanium Substrate with PEELER Technology

III–V solar cells are mainly grown on GaAs or Ge substrate, which significantly contributes to the final cost and affects the sustainable use of these rare materials. A so‐called PEELER process is developed, in which a porosification technique is used to create a weak layer between a Ge substrate and the epitaxial layers. This method enables the separation of the grown layers, allowing for the subsequent reuse of germanium and a reduction in the environmental and economic cost of optoelectronic devices. Technology validation using the device performance is important to assess the technology interest. For this purpose, the performance of 22 nondetached single‐junction GaAs photovoltaic cells grown and manufactured on porosified 100 mm Ge wafer without antireflection coating is fabricated and compared. All the cells exhibit comparable performance to state‐of‐the‐art GaAs solar cells (grown or Ge or GaAs) with high efficiency (21.8% ± 0.78%) and thereby demonstrate the viability of growing high‐performance optoelectronic devices on detachable Ge films.

Simulation of left-handed materials for GaAs solar cells

The optical performance of photovoltaic solar cells and modules is affected by the significant reflection losses at the air/glass front interface. Several antireflection coating materials on solar glass are introduced to overcome this drawback as a mechanism for light trapping. We propose in this study a novel structure containing silicon nitride (SiNx), left-handed materials (LHMs), and the light absorbing material (gallium arsenide, GaAs), to minimize the reflection and increase the light absorption. The transfer matrix method was used to compute the reflectivity and absorption of both normal and transverse magnetic polarized light. The results show that left-handed materials have an available good impact on the efficiency of solar cells by increasing the light absorption through the proposed structure where the absorbance achieves values greater than 80% in the entire light spectrum.

Multi-Directional Displacement Threshold Energy and Crystal Irradiation Damage Model

Subject to intense high-energy particle irradiation, various effects manifest within a material. Specifically, when high-energy particles collide with lattice atoms in a crystal material, a sequence of interactions is set in motion, initiating irradiation effects. Using GaAs solar cells as an example, this study investigates how potential barriers in different directions of atoms in sphalerite structures affect atomic displacement and establishes a probability model for lattice atomic displacement under proton irradiation. By combining Markov chains, changes in displacement threshold energy with different crystal orientations are described, and a damage model for cascading collision relationships that cause irradiation effects is established. Finally, the new model is compared to classical models, and differences in defects caused by proton impacts at several energies on GaAs crystals are simulated.

GaAs thin-film solar cells for perfect absorption in the visible and near-infrared bands

Improving the solar cell's ability to capture solar photons and enhancing its absorption of light have a significant impact on increasing the photoelectric conversion efficiency (PCE) of solar cells. In this study, we propose to embed a layer of light-trapping structure (LTS) utilizing Ti nanoparticles and their oxide TiO2 periodically arranged in the window layer of GaAs thin-film solar cells. This structure improves the light absorption efficiency by increasing the optical range and surface plasmon resonance of light inside the cell, which in turn improves the PCE of the solar cell. Simulation results show that the GaAs solar cell proposed in this paper achieves an average absorptivity of 94.99% in the visible and near-infrared wavelength bands, and the PCE reaches 31.77%, which is close to the Shockley-Queisser limit level of the single-junction solar cell. And it realizes the characteristic of perfect absorption in the wavelength range of 555–800 nm. The cell structure proposed in this study is characterized by high bandwidth perfect absorption and high PCE, which is insensitive to the angle of incidence, and provides a new idea for the design of new high-efficiency thin-film solar cells.

Failure mechanism of parallel gap resistance welding joint between Ag foil and GaAs solar cell by temperature cycling

Reliability of joints in solar arrays significantly influences the service life of satellites. Interface between solar cell and interconnector experiences serious temperature cycling during space service which would further lead to failure. To further improve the interface joining thermal reliability, elucidation of the interface formation and corresponding microstructure evolution during thermal fatigue is necessary. In this study, parallel gap resistance welded (PGRW) multi-layered joint between GaAs solar cell and Ag foil are subjected to different temperature cycling tests (−160–120 °C, −165–160 °C) with various cycles. Obtained results confirm the joining mechanism of the joint as solid-solution interdiffusion between Ag foil and Au surface of solar cell electrode. Also, conducted temperature cycling essentially lead to thermal fatigue process at Ag/Au interface, therefore more serious interface strength degradation is generated by larger temperature cycling range. Joint failure is initiated by thermal fatigue induced dislocation and residual strain concentrations around dissimilar interface. And the large mismatch in coefficients of thermal expansion (CTE) of the multilayer structure amplifies the thermal fatigue effect.

Comparative Study of Polarization‐Dependent Conversion Efficiency of GaAs and Si Solar Cells at Oblique Incident Angles Using Surface DLAR Coating of MgF2/ZnSe

AbstractThe aim of this work is to minimize reflection losses in order to increase the efficiency of solar cells by using anti‐reflection coatings (ARCs). Despite extensive research on improving solar cell conversion efficiency at normal incidence, development at angle of incidence has received little attention. Thus, the reflectivity of single‐layer ARC (SLARC) MgF2 and ZnSe, double‐layer ARC (DLARC), MgF2/ZnSe on Si, and GaAs substrates at transverse electric (TE) and transverse magnetic (TM) modes of polarization in the visible and near‐IR regions for different angles of incidence is analyzed. The optical and electrical properties of Si and GaAs solar cells are analyzed by using the reflectance spectra of SLARC and DLARC at various angles of incidence for the TM and TE modes of polarization under the solar power spectrum (AM1.5). The achieved results due to the effect of DLARC are compared for Si and GaAs solar cells. From these analyses, it is concluded that MgF2/ZnSe is an appropriate DLARC for the range of wavelengths 400–800 nm at 10°–30° angles of incidence in TM mode for tuning the optical and electrical properties of Si and GaAs substrates for terrestrial applications.

Simulation study of TiO2 single layer anti-reflection coating for GaAs solar cell

Anti-reflection coating (ARC) plays an important role in reducing the reflection of incident light and absorbing more photons to produce more photoelectrons. In this paper, a single-layer TiO2 anti-reflection coating is performed on GaAs solar cells. In the simulation study, we compared the solar cell before and after ARC by using PC1D simulation software. The I–V characteristics, reflectance, and external quantum efficiency have been simulated with a refractive index of 2.324 at 600 nm wavelength. The simulated results show that the ARC-coated solar cell performs better. It is found that the power conversion efficiency of 24.75% reflection is 9.5%, and the EQE is 95% at the 62 nm thickness of the ARC layer. The optimized reflectivity was found to be around 5%, which is quite lower than that without ARC (32%).

Joining mechanism of connection between Ag-plated Kovar interconnector and stranded Ag-plated Cu wire produced via parallel gap resistance welding

A space solar array includes GaAs solar cell, interconnector, and stranded Cu wire. Due to the preferential high working efficiency, the assembly of solar array is mostly performed using parallel gap resistance welding (PGRW). Since strengthening of the PGRW joints is the key to further extend service life of solar array, it is necessary to elucidate joining mechanism of each connection. In the present research, to clarify the controversy over PGRW joining mechanism between Ag-plated Kovar interconnector and stranded Ag-plated Cu wire, various advanced material characterization methods are conducted to joining interfaces. Experimental results confirm that, in addition to the known Ag/Cu eutectic interface, solid evidence of metallurgy bonding is also found in Cu/Cu interface. Such finding has significant implication for further enlarge the PGRW process window and produce stronger joints.

Research on the Application of Domestic High-Modulus Carbon Fiber/Epoxy Composites to Solar Panels for Solar Arrays

Based on the new high-modulus carbon fiber CCM40J-6k, which is the critical raw material of a solar panel, the molding process of a mesh face sheet combined with epoxy resin, the overall mechanical performance of a mesh face sheet combined with aluminum honeycomb, the compatibility with polyimide insulation film + solar cell circuit, and the space environment adaptability must pass a test verification and assessment as the premise for large-scale orbit applications. Therefore, based on the traditional carbon fiber M40JB-6k as a reference, a systematic verification project was conducted to apply the CCM40J-6k carbon fiber composite at the process, component, and assembly levels. Six aspects of testing and verifying items were conducted, including mechanical properties under room temperature and thermal shock conditions, bonding force of mesh nodes, comparison of the adaptability of domestic and imported carbon fiber substrates to high–low temperature alternation, the ability of domestic carbon fiber substrates to adapt to the thermal environment after laying solar cell circuits, and in-orbit lifespan of solar panels. Based on the verification results, the mechanical properties of the substrate are the same as those of the imported M40JB-6k, and the actual molding process for M40JB-6k can be utilized. Sample pieces of the substrates can withstand the thermal shock and thermal cycling tests. The bending stiffness of the sample pieces before and after the tests is 3.5%~9.6% higher, and the bending strength is 4.2%~7.2% lower. The tensile strength of mesh nodes made of domestic carbon fiber is 18.9% higher than that of mesh nodes made of imported carbon fiber. The CCM40J-6k substrate is similar to triple-junction GaAs solar cells. The change rates of the open-circuit voltage and the short-circuit current of solar panels based on domestic carbon fiber after fatigue thermal cycling with 2070 cycles are 0.55% and 0.24%, respectively. The above results indicate that the comprehensive performance of the domestic carbon fiber CCM40J-6k meets the requirements and can be applied to solar panels for solar arrays.