Search Results (32)

Back surface field (BSF) materials are key functional layers that suppress rear-surface recombination and regulate carrier transport in III–V solar cells. This work investigates the performance degradation behavior of GaInP solar cells with AlInP and AlGaInP BSF layers under 1 MeV electron irradiation. Through a combination of optoelectronic measurements and TCAD simulations, the carrier transport and recombination mechanisms before and after irradiation are comprehensively analyzed. Although both devices deliver comparable initial photovoltaic performance, distinct degradation trends emerge under high-fluence electron irradiation. After a cumulative fluence of 1 × 10¹⁵ e/cm², the cell with an AlInP BSF suffers more severe degradation owing to inferior radiation hardness. Irradiation-induced defects reduce the minority-carrier lifetime and enhance Shockley–Read–Hall (SRH) nonradiative recombination, resulting in a 14% drop in short-circuit current density. In contrast, the AlGaInP BSF exhibits favorable radiation tolerance, and the corresponding device undergoes only a 2% loss in short-circuit current density. The influence of the BSF structure on carrier transport and recombination is systematically analyzed, providing experimental and theoretical support for the design of space-grade GaInP top cells. Full article

Space missions working under harsh heliocentric conditions demand more efficient photovoltaics operating under high solar concentration, high temperatures, and harsh radiation conditions. Although most simulation work has been conducted using the terrestrial AM1.5 spectrum, AM0 high concentrators are of great importance to realistic satellite missions. Though III–V multijunction solar cells are currently the norm in space applications, their efficiency under extremely high solar concentration ratios is not yet optimized to support future space missions. This work designs and numerically optimizes a GaAs VTJ solar cell using SILVACO ATLAS software (5.40.0.R). In the optimization, the thickness of the front and back layers, as well as the doping profile within the emitter, base, and tunnel junction regions, were adjusted. The important PV semiconductor attributes, including the short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF), and efficiency (η), were examined over a concentration factor ranging between 1 and 10,000 suns. The efficiency of the optimized VTJ solar cell increased from 20.4% at 1 sun to 26.0% at 10,000 suns. This is mainly due to the near-linear increase in Jsc and the stable FF, which remains between 87% and 89%. In addition, the solar cell shows a steady increase in Voc between 1.85 V and 2.33 V. An optimized GaAs VTJ solar cell design is a promising component in future space missions, which require high power density and are suited to operating under high heliocentric orbits, such as in the Parker Solar Probe and solar-electric propulsion systems. Full article

GaAs_1-xN_x/GaAs (001) (0 < x ≤ 0.037) tensile-strained epilayers are of considerable importance in optoelectronics due to their ability to offer large and resilient band structure engineering. Strain causes valence-band splitting, giant bandgap reduction and phonon frequency shifts. Optimum performance of III-V-Ns in long-wavelength lasers, infrared photodetectors, optical modulators, and multi-junction solar cells is contingent on their distinctive vibrational and optical characteristics. We report results of meticulous simulations of GaAs_1-xN_x alloys to validate Fourier transform infrared (FTIR) reflectivity and spectroscopic ellipsometry (SE) data in the far-infrared and ultraviolet regions. The FTIR spectra showed strong reflectivity peaks and dips in the reststrahlen band region, linked to the transverse optical ${\omega }_{\mathrm{T}\mathrm{O}1}$ and longitudinal optical ${\omega }_{\mathrm{L}\mathrm{O}1}$ modes of the Ga-As bond and a high-frequency ${\omega }_{\mathrm{T}\mathrm{O}2}$ local vibrational mode of GaAs:N. Modified dielectric functions of GaAs_1-xN_x/GaAs epilayers are carefully evaluated using an improved Adachi’s semiemperical method to study the x and E-dependent optical constants. Focusing on the electronic band structures at critical points, this approach provided accurate analytical formulation to evaluate complex dielectric $\tilde{\epsilon }$(E) and refractive indices $\tilde{\mathrm{n}}$(E) for simulating reflectance spectra in a wide energy range with good agreement to the SE data. Full article

Multijunction solar cells employing a GaInP/GaAs/Ge triple-junction configuration are the dominant technology for space photovoltaic applications. The choice of an efficient electrode is crucial in solar cells, as it enables effective charge carrier collection and transport while allowing maximum light to reach the active layer. Indium tin oxide (ITO)/graphene hybrid electrodes have emerged as smart transparent conductors offering significant advantages over conventional brittle ITO films. Graphene electrodes were prepared by cold-wall chemical vapor deposition and ITO electrodes were commercially obtained and used as a base for hybrid ITO/graphene electrodes. Raman spectroscopy confirmed the successful integration and characteristic G and 2D bands on the ITO surface. Nanoscale current mapping via Tunneling Atomic Force Microscopy (TUNA-AFM) verified continuous conductive pathways throughout the film with ~60% increase in nanoscale tunneling current at graphene/ITO interfaces, indicating improved local charge transport pathways. These results demonstrate the suitability of ITO/graphene hybrid electrodes a promising material for multijunction solar cells and other aerospace technologies. Full article

Space photovoltaics remains the primary power source for satellites and spacecraft, where high efficiency, radiation resistance, and low mass are essential requirements. While conventional III–V multijunction solar cells currently represent the technological benchmark, recent advances in materials science and device architectures have significantly expanded the design space of space photovoltaic systems. This review provides a comprehensive overview of the fundamental physical principles, material platforms, and device concepts relevant to photovoltaic operation under space conditions, with particular emphasis on the AM0 spectrum, radiation effects, and thermal cycling. Special attention is devoted to advanced architectures, including inverted metamorphic multijunction solar cells, concentrator photovoltaic systems, and emerging tandem concepts such as perovskite/silicon and all-perovskite devices. The review highlights the growing importance of system-level metrics, particularly specific power and integration flexibility, which increasingly complement efficiency as key performance indicators. Although emerging technologies offer unprecedented opportunities for lightweight and high-efficiency photovoltaic systems, challenges related to long-term stability, defect control, and scalability remain critical for their practical implementation. Overall, the future of space photovoltaics lies in the development of application-specific solutions that balance efficiency, durability, mass, and cost, enabling next-generation space missions and energy systems. Full article

Multijunction laser power converters are demonstrated for the first time with high efficiencies for average optical irradiances exceeding 150 W/cm². The GaAs-based photovoltaic power converting III-V heterostructures are designed with six GaAs subcells having an area of 0.14 cm², receiving up to 22 W of input power at ~811 nm, delivering over 14 W of output power. The maximum efficiencies are obtained in the range of 30 to 75 W/cm², and efficiencies > 64% are still obtained at 160 W/cm². The efficiency reduction for higher irradiance values originates predominantly from residual heat generated in the active layers. For example, in 100% duty factor measurements, the bandgap voltage offset saturates to W_oc ~ 170 mV. However, in pulsed mode, W_oc values as low as 150 mV have been obtained for a device base temperature of 20 °C. For smaller 0.029 cm² devices, W_oc values around 137 mV are obtained at 240 W/cm². Full article

The significant disparity between the size and electronegativity of N and group-V (P, As, Sb) atoms in dilute III–V-Ns remains a cornerstone for developing the next-generation electronics. Variations in the structural, optical, and phonon properties of the quaternary GaAs_1−x−ySb_yN_x alloys are being used for improving the high-performance photovoltaic energy and optoelectronic technologies. Bandgap ${\mathrm{E}}_{\mathrm{g}}$ tunability has assisted efficient light emission/detection to cover the crucial optical fiber wavelengths for the low-cost integrated chips in data communications and sensing devices. The lattice dynamical properties of these materials are critical for assessing the reliability to evaluate the performance of long-wavelength lasers, photodetectors, and multi-junction solar cells. Our systematic Raman measurements on high-quality MBE grown $\mathrm{G}\mathrm{a}{\mathrm{A}\mathrm{s}}_{0.946}{\mathrm{S}\mathrm{b}}_{0.032}{\mathrm{N}}_{0.022}$/GaAs samples have detected ${\mathsf{\omega }}_{\mathrm{T}\mathrm{O}\left(\mathsf{\Gamma }\right)}^{\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}}$ and ${\mathsf{\omega }}_{\mathrm{T}\mathrm{O}\left(\mathsf{\Gamma }\right)}^{\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}}$ phonons along with a high frequency N_As local mode near ~476 cm⁻¹. Weak phonon structures on both sides of the broad 476 cm⁻¹ band are interpreted forming a complex N_As–Ga–Sb_As defect center. Using a realistic rigid-ion model in the Green’s function framework, the simulations of impurity modes for isolated and complex defects have provided corroboration to the experimental data. Full article

The calculation of the limiting efficiency and structural optimization of solar cells based on the detailed balance principle is systematically investigated in this study. Through modeling and numerical simulations of various cell architectures, the theoretical efficiency limits of these structures under AM1.5G (Air Mass 1.5 Global) spectrum were quantitatively evaluated. Through a comprehensive consideration of the effects of bandgap and composition, the Al_0.03Ga_0.97As/Ge (1.46 eV/0.67 eV) cell configuration was determined to achieve a high theoretical efficiency of 43.0% for two-junction cells while maintaining satisfactory lattice matching. Furthermore, the study proposes that incorporating a Ga_0.96In_0.04As (8.3 nm)/GaAs_0.77P_0.23 (3.3 nm) strain-balanced multiple quantum wells (MQWs) structure enables precise bandgap engineering, modulating the effective bandgap to the optimal middle-cell value of 1.37 eV, as determined by graphical analysis for triple junctions. This approach effectively surpasses the efficiency constraints inherent in conventional bulk-material III–V semiconductor solar cells. The results demonstrate that an optimized triple-junction solar cell with MQWs can theoretically achieve a conversion efficiency of 51.5%. This study provides a reliable theoretical foundation and a feasible technical pathway for the design of high-efficiency solar cells, especially for the emerging MQW-integrated III–V semiconductor tandem cells. Full article

Multiband solar cells offer a promising route to surpass the Shockley-Queisser limit by harnessing sub-bandgap photons through three active energy band transitions. However, realizing their full potential requires overcoming key challenges in material design and device architecture. Here, we propose a novel multiband stacked anti-parallel junction solar cell structure based on highly mismatched alloys (HMAs), in particular dilute GaAsN with ~1–4% N. An anti-parallel junction consists of two semiconductor junctions connected with opposite polarity, enabling bidirectional current control. The structures of the proposed devices are based on dilute GaAsN with anti-parallel junctions, which allow the elimination of tunneling junctions—a critical yet complex component in conventional multijunction solar cells. Semiconductors with three active energy bands have demonstrated the unique properties of carrier transport through the stacked anti-parallel junctions via tunnel currents. By leveraging highly mismatched alloys with tailored electronic properties, our design enables bidirectional carrier generation through forward- and reverse-biased diodes in series, significantly enhancing photocurrent extraction. Through detailed SCAPS-1D simulations, we demonstrate that strategically placed blocking layers prevent carrier recombination at contacts while preserving the three regions of photon absorption in a single multiband semiconductor p/n junction. Remarkably, our optimized five-stacked anti-parallel junctions structure achieves a maximum theoretical conversion efficiency of 70% under 100 suns illumination, rivaling the performance of state-of-the-art six-junctions III-V solar cells—but without the fabrication complexity of multijunction solar cells associated with tunnel junctions. This work establishes that highly mismatched alloys are a viable platform for high efficiency solar cells with simplified structures. Full article

Most commercially available InGaP/InGaAs/Ge triple-junction solar cells suffer from current mismatch due to the excess current generated by the Ge sub-cell. Combining epitaxial germanium with III–V materials would enable the realization of lattice-matched four- or five-junction solar cells, where the near-infrared spectrum could be split between two Ge sub-cells instead of one, thereby eliminating current mismatch in these devices and achieving higher conversion efficiency. In this work, we present the first demonstration of a quadruple-junction (4J) InGaP/InGaAs/Ge/Ge device, with all layers sequentially deposited in the same MOVPE growth chamber. The 4J device also features a novel architecture that exploits the “transistor effect” between the two Ge junctions to eliminate the current mismatch in the upper 3J InGaP/GaAs/Ge part. We describe the growth and the cell structure realization strategy developed to overcome—and, where beneficial, to exploit—the cross-contamination between III–V and group IV elements, thus avoiding the need for two separate deposition systems. The structural and electrical characterizations performed to ascertain the 4J device quality are presented. This result represents a key step toward the realization of highly efficient, all-MOVPE-grown, lattice-matched MJ solar structures that combine III–V and group IV alloys. Full article

High-efficiency multijunction laser power converters are demonstrated for the first time at high power for optical inputs around 1070 nm. The InP-based photovoltaic power-converting III–V heterostructures are designed with eight lattice-matched InGaAsP subcells (PT8-1070 nm). Conversion efficiencies of 55% were obtained at 18 W of output power. Endurance testing was performed for over 1000 h of continuous operation with an average output power of 13.2 W at an input wavelength of 1064 nm. An average steady-state efficiency of 54.4% at an ambient temperature of ~20 °C was obtained for that duration. The results demonstrate that 1 cm² optical power converter devices can produce electrical outputs of 20 W at maximum power voltages around V_mpp ~6 V, thus retaining an optimal load near R_mpp at ~2 ohms. Efficiencies between 57.9% and 59.0% were also obtained for smaller 0.029 cm² chips for input intensities between 35 and 69 W/cm². This is an important development for power beaming applications: the unprecedented combination of power and conversion efficiency capabilities is expected to enable deployments for key wavelengths between 1040 and 1080 nm. Full article

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. Full article

Improvement of triple-junction (3J) III-V/Ge solar cells efficiency is hindered by the low current produced by the top and middle cells relative to the bottom cell (Ge). This can be explained by the difficulty of characterizing, on an individual basis, the subcells. We investigate the fabrication process of multi-terminal multi-junction solar cells (MTMJSC) and its potential as a promising architecture to independently characterize subcells of multi-junction solar cells. Here, we study monolithic triple-junction solar cells, with an InGaP top cell, an InGaAs middle cell and a Ge bottom cell interconnected by tunnel junctions. We demonstrate a fabrication process for MTMJSC on commercial wafers for characterization applications purposes. I-V measurements, under illumination, of two-terminals and MTMJSC were compared to validate that the MTMJSC fabrication process does not degrade the cells’ performance. The dark current of each subcell was also measured and an ideal-diode model used to determine the subcells electrical parameters. The results suggest a method to measure the relative absorption and the opto-electrical couplings between the subcells unambiguously, through EQE and electroluminescence measurements, based on basic micro-fabrication processes. Full article

Multi-junction photovoltaics approaches are being explored to mitigate thermalization losses that occur in the absorption of high-energy photons. However, the design of tandem cells faces challenges such as light reflection and parasitic absorption. Nanostructures have emerged as promising solutions due to their anti-reflection properties, which enhances light absorption. III-V nanowires (NWs) solar cells can achieve strong power conversion efficiencies, offering the advantage of potentially integrating tunnel diodes within the same fabrication process. Metal halide perovskites (MHPs) have gained attention for their optoelectronic attributes and cost-effectiveness. Notably, both material classes allow for tunable bandgaps. This study explores the integration of MHPs with III-V NWs solar cells in both two-terminal and three-terminal configurations. Our primary focus lies in the optical analysis of a tandem design using III-V semiconductor nanowire arrays in combination with perovskites, highlighting their potential for tandem applications. The space offered by the compact footprint of NW arrays is used in an interpenetrated tandem structure. We systematically optimize the bottom cell, addressing reflectivity and parasitic absorption, and extend to a full tandem structure, considering experimentally feasible thicknesses. Simulation of a three-terminal structure highlights a potential increase in efficiency, decoupling the operating points of the subcells. The two-terminal analysis underscores the benefits of nanowires in reducing reflection and achieving a higher matched current between the top and the bottom cells. This research provides significant insights into NW tandem solar cell optics, enhancing our understanding of their potential to improve photovoltaic performance. Full article

Recent developments in long wavelength and cryogenic laser power converters have unlocked record performances in both areas. Here, devices for an optical input at ~1470 nm are studied for cryogenic applications, combining these cryogenic and long-wavelength attributes. Multijunction laser power converters are demonstrated to have a high-efficiency operation at 77 K. The photovoltaic-power-converting III-V semiconductor devices are designed with InGaAs-absorbing layers, here with 10 thin subcells (PT10), connected by transparent tunnel junctions. Unprecedented conversion efficiencies of up to 67.5% are measured at liquid nitrogen temperatures with an output power of P_mpp = 1.35 W at an average optical input intensity of ~62 W/cm². A remarkably low bandgap voltage offset value of W_oc~50 mV is obtained at an average optical input intensity of ~31 W/cm². Full article