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Particle count (Candela CS20 by KLA Tencor) on 4-inch Si (a) before and (b) after emitter formation. (c) Scanning acoustic microscope image of 4-inch GaAs//Si bonded in Ayumi SAB200. (d) Infrared transmission image of a 3J GaInP/GaAs//Si solar cell bonded in the EVG580 ComBond.
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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 $_{x}$...
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Context 1
... shown in Fig. 2(a), the number of particles found on c-Si by optical surface analysis (Candela CS20 measurement, calibrated on a flat surface with microspheres) is only marginally increased [see Fig. 2(b)] after the process steps for bottom cell emitter formation (phosphorus implantation and annealing). Additionally, a prebonding megasonic cleaning ...
Context 2
... shown in Fig. 2(a), the number of particles found on c-Si by optical surface analysis (Candela CS20 measurement, calibrated on a flat surface with microspheres) is only marginally increased [see Fig. 2(b)] after the process steps for bottom cell emitter formation (phosphorus implantation and annealing). Additionally, a prebonding megasonic cleaning step was performed on both wafer surfaces to further reduce the particle density. With this process flow, nearly void-free bonds over the full 4-inch wafer area are obtained, as visible in ...
Citations
... The advancement of tandem devices utilizing III-V semiconductor materials and silicon has been considerably influenced by the lattice distortion and thermal expansion coefficient discrepancies between the two materials. In addition to the high capital and operating costs, tandem devices struggled with these issues [13]. Utilizing the advantages of perovskite materials-known for their direct bandgap, high absorption coefficient, and superior charge transport properties-researchers have been designing and optimizing tandem solar cells. ...
Tandem solar cells are widely considered the industry’s next step in photovoltaics because of their excellent power conversion efficiency. Since halide perovskite absorber material was developed, it has been feasible to develop tandem solar cells that are more efficient. The European Solar Test Installation has verified a 32.5% efficiency for perovskite/silicon tandem solar cells. There has been an increase in the perovskite/Si tandem devices’ power conversion efficiency, but it is still not as high as it might be. Their instability and difficulties in large-area realization are significant challenges in commercialization. In the first part of this overview, we set the stage by discussing the background of tandem solar cells and their development over time. Subsequently, a concise summary of recent advancements in perovskite tandem solar cells utilizing various device topologies is presented. In addition, we explore the many possible configurations of tandem module technology: the present work addresses the characteristics and efficacy of 2T monolithic and mechanically stacked four-terminal devices. Next, we explore ways to boost perovskite tandem solar cells’ power conversion efficiencies. Recent advancements in the efficiency of tandem cells are described, along with the limitations that are still restricting their efficiency. Stability is also a significant hurdle in commercializing such devices, so we proposed eliminating ion migration as a cornerstone strategy for solving intrinsic instability problems.
... For use in space applications to overcome the limitations of Si-cells, multijunction solar cells (MJSC) have been constructed. MJSCs are significantly more efficient than Si-based ones by over 10% [77]. In Fig. 3-12 (a) and (b) for reference the LEO and terrestrial spectra are shown. ...
The Electrical Power System (EPS) is the most important of the numerous subsystems
that make up the SmallSat since an unstable power supply to the others frequently
compromises the mission. The EPS is made up of electrical sources, storage units, and
loads that are all connected via various power converters. The operation of the various
power converters that make up the EPS must be carefully coordinated to achieve
efficient photovoltaic power use, reliable power delivery, and ideal battery
management. Due to the coordination and control of distributed generation (DG),
storage, and loads in a small-scale electrical network, a SmallSat EPS can be viewed
as a space microgrid in terms of power systems. At the same time, managing the
charge/discharge cycle of the battery, pulse, peak, and transient power demand to
prevent instability and performance degradation of the spacecraft is difficult due to
the demanding requirements of their design, which include harsh radiation, space,
weight, and varying temperatures. Therefore, selecting an appropriate EPS design,
control, and power management are major elements for a long-lasting and successful
satellite mission. In this respect, this thesis presents a comprehensive review of EPS
architectures, converter topologies, and technologies dedicated to the SmallSat
microgrids. Relevant technical challenges will be identified and addressed by
considering space conditions to guarantee the extended satellite mission life. Besides,
sophisticated design, control, and power management strategies are introduced and
analyzed. As opposed to the current specific mission designs, a generalized and fullscale EPS design will be proposed where the design and modeling of PV, converter,
and battery sizing will be considered and examining the power supply and demand of
the satellite, which is dependent on PV array cyclic power generation and battery cell
nonlinear behavior. To guarantee that necessary duties are carried out effectively and
without power shortages throughout the satellite mission, first, the suitable EPS model
with solar panel converter architectures and configurations including battery energy
storage will be derived. The proposed design considers load profile, operating modes,eclipse, and altitude. A 3U CubeSat configuration operating under various load,
temperature, and irradiance circumstances show the effectiveness of this design and
power management. The design verification demonstrated good results in several
operational modes across a wide range of temperatures and irradiance. Secondly, for
tiny satellite applications, a comparative analysis of Maximum Power Point Tracking
(MPPTs) in spinning situations will be developed. Due to the volume and mass
limitations of the Nano Satellite (NanoSat), which have solar panels installed on their
bodies, these satellites are designed to operate in a variety of unusual orientation
scenarios. As a result, the PV system's unpredictable solar irradiation is caused, and
an efficient PPT technique is required to extract the most power possible to transfer
to the loads in the NanoSat Electrical Power System (EPS). To confirm the best MPPT
extractions for NanoSat applications, several well-known MPPT approaches are
analyzed for optimal power extraction. These include the traditional Perturb and
Observe (P&O), Incremental Conductance (IC), and Ripple Correlation Control
(RCC) methods. In contrast to the IC and RCC, the P&O extracts less power while
oscillating more. In comparison to RCC, the IC method extracts greater power. RCC,
in contrast to IC, is smoother and exhibits fewer oscillations. A power management
control technique has lastly been established for SmallSat microgrid applications to
avoid overcharging batteries while monitoring the PV Maximum Power Point (MPP)
and Battery State of Charge (SOC) limits under a variety of solar and load scenarios.
This suggested power management system uses an intelligent algorithm that can
switch between maximum power point tracking and current control mode depending
on the battery's state of charge to optimally manage solar power generation. The
implied control and management system tends to prolong battery life through
controlled charging in addition to enabling the best solar power extraction. For a
seamless inter-mode transition, a local link is in charge of transmitting data about the
battery's state of charge. To prevent battery overcharging, the suggested control and
energy management system under incident load needs can limit PV power extraction.
At various profiles of load and incident irradiance, the results are examined for powersharing among solar PV, battery, and load to validate the effectiveness of the proposed
full-scale EPS design, MPPT, and power management system for SmallSat
applications. The proposed EPS design, power electronic control, and power
management systems are modeled in MATLAB/SIMULINK.
... However, there has recently been a renewed interest in the integration of III-V materials on Si, driven by the potential applications for photovoltaics. Currently, the most developed techniques for such integration are direct epitaxial growth [7][8][9], wafer bonding [10], [11] and mechanical stacking [12]. However, even though wafer bonding and mechanical stacking have given higher solar cell than direct epitaxial growth [13], this last one implies a significant cost reduction since no III-V substrates are required. ...
Integration of GaP layers on silicon substrates using AsH3 pre-exposure followed by a PH3-based GaP epitaxial growth allows the development of very promising processes for the photovoltaic industry, although many of the growth routines using this approach suffer from reproducibility issues when transferred to a new epitaxial system, leading to poor quality layers. This fact reveals a lack of knowledge on the mechanisms behind the formation of the most common planar defects (stacking faults and microtwins) and their dynamics for GaP/Si Metal Organic Vapor Phase Epitaxy using AsH3 and PH3. Therefore, in this work, a set of GaP/Si samples with a similarly high defect density grown between 700 °C and 725 °C, are analyzed by means of high-resolution scanning transmission electron microscopy and electron energy loss spectroscopy. The results presented show contaminant-free Si surfaces for temperatures above 725 °C, ruling out the hypothesis of contaminant as the origin of these planar defects. Regarding the interface Si/GaP, the GaP growth starts, in all the samples, with GaSi bonds. Additionally, no traces of As are found, which reinforces the hypothesis of an effectively displacement of As on Si surface by Ga atoms at high temperature. Finally, it is observed complex chemical structures in the origin of the microtwins and the cause of the origin of these defects seems to be a localized gallium depletion at the GaP/Si interface.
... Based on the view that the cost of MJ cells was lowered by placing subcells on Si-based cells, the bonding of III-V subcells to Si or SiGe was explored to form MJ cells. [28][29][30][31][32][33][34] GaAs wafers used for the growth of III-V subcells should be reused to further reduce the fabrication cost of MJ cells. Epitaxial lift-off (ELO) process from GaAs wafers 35,36) was applied to III-V cell fabrication. ...
Recent achievements in research of heterojunctions fabricated using surface activated bonding (SAB), one of the practically useful direct wafer bonding technologies, are discussed. The response of bonding interfaces to post-bonding annealing is focused. These junctions reveal high thermal tolerance (1000 ○ C in case of junctions made of widegap materials) despite difference in coefficients of thermal expansion between bonded materials. Defect layers with a several-nm thickness formed by the surface activation process at the as-bonded interfaces get faint and their electrical and mechanical properties are improved by annealing. These results show that as bonded interfaces are in a metastable state, and novel functional devices are likely to be realized by applying wafer processing steps to SAB-based junctions. Characteristics of III-V//Si multijunction solar cells, GaN-on-diamond high electron mobility transistors, and metal-foil based low-loss interconnects that are fabricated by processing SAB-based junctions are described, and the future prospects are presented.
... The multijunction device optimized for peak sun may underperform drastically under morning and late afternoon sun. Hence presently, a PV cell with the ideal combination of materials is not available yet, but researchers around the world are working on various technologies, such as metamorphic growth [32], wafer bonding [33], multi-quantum wells [34], and inverted stacks [35]. Though technologically, these processes look promising, the high cost involved in these processes will remain a barrier for application as flat panels [36] in the near future, and their commercial applications may be limited to concentrated PV systems only. ...
Link for free download https://authors.elsevier.com/a/1dIAb7tDQ9Gxkh ************************************************************************************* Presently, the world is going through a euphoric rush to install photovoltaic (PV) devices in deserts, over water bodies, on rooftops of houses, vehicles, and parking spaces, and many other applications. The cumulative PV installation is estimated to have crossed 600 GW globally to date and is expected to cross 4500 GW by 2050 due to sustained investment and continual innovation in technology, project financing, and execution. This article presents a critical and comprehensive review of the wide spectrum of present and future PV technologies, not only in terms of their performance but also in terms of the aspects of their end-of-life waste management and ecotoxicity, which have been largely neglected by the researchers and policymakers. The global status of the regulatory framework is reviewed as well, with regard to the life cycle management of PV waste. And It is found that presently, the world is very poorly equipped with regulatory frameworks to deal with massive PV waste (about 78 million tonnes), expected to be generated by 2050. Based on the findings, an immediate and disruptive paradigm shift is proposed in the policy framework, from the promotion of new PV installation to life cycle management of PV assets.
... Detailed descriptions of the theory of multi-junction solar cell are available in [1][2][3][4]. The authors in [5][6][7] show the development of III-V-onsilicon solar cell. The GaInP/GaAs//Si solar cell reported in [5] has reached 33.3% conversion efficiency under 1-sun AM1.5G. ...
... Assuming the circuit current is limited by j sub-cell, the recombination current ('or reverse saturation current') of i sub-cell can be expressed as J rec,1 = J 1 − J 2 − J LC12 . Then Equation (6) can be obtained by taking J rec,1 back into Equation (5). ...
The luminescent coupling effect in multi-junction solar cell is a phenomenon where extra photocurrent in one sub-cell is driven by radiative recombination of electron–hole pairs in another sub-cell. This paper focuses on the analysis of the modeling of luminescent coupling effect in multi-junction solar cell. These modelings are based on the two-diode equivalent circuit. Finally, it concludes that the study of the luminescent coupling effect requires not only a suitable modeling but also a good experimental method for detecting the characteristics of sub-cells in multi-junction solar cell.
... 65,116 The two wafers are mechanically pressed, forming an almost uniform bonding area as shown in Fig. 14(a). Then, the upper substrate is removed, so far most successfully by complete chemical etching of the substrate, 107,108,114,116,118 or by substrate lift-off after chemically etching a sacrificial layer (epitaxial lift-off or ELO). 119,120 Other possibilities include ion implantation, laser-and stressinduced lift-off, which are common in other fields but less explored here. ...
... In any case, a tunnel diode between Si and the first III-V subcell is still required, and is usually done on the III-V structures. With this wafer bonding strategy, Si-based 2J devices have reached 30.2% AM 1.5G efficiency, 118 30.0% under concentrated light, 107 and 3J III-V bonded on Si have achieved 34.5% under AM 1.5G, the latter achieved very recently at the end of 2020. ...
As the photovoltaic (PV) sector approaches 1 TW in cumulative installed capacity, we provide an overview of the current challenges to achieve further technological improvements. On the raw materials side, we see no fundamental limitation to expansion in capacity of the current market technologies, even though basic estimates predict that the PV sector will become the largest consumer of Ag in the world after 2030. On the other hand, recent market data on PV costs indicates that the largest cost fraction is now infrastructure and area-related, and nearly independent of the core cell technology. Therefore, additional value adding is likely to proceed via an increase in energy yield metrics such as the power density and/or efficiency of the PV module. However, current market technologies are near their fundamental detailed balance efficiency limits. The transition to multijunction PV in tandem configurations is regarded as the most promising path to surpass this limitation and increase the power per unit area of PV modules. So far, each specific multijunction concept faces particular obstacles that have prevented their upscaling, but the field is rapidly improving. In this review work, we provide a global comparison between the different types of multijunction concepts, including III-Vs, Si-based tandems and the emergence of perovskite/Si devices. Coupled with analyses of new notable developments in the field, we discuss the challenges common to different multijunction cell architectures, and the specific challenges of each type of device, both on a cell level and on a module integration level. From the analysis, we conclude that several tandem concepts are nearing the disruption level where a breakthrough into mainstream PV is possible.
... Because a multi-junction cell can surpass the SQ limit of a single-junction cell, multi-junction cells have been intensively investigated in various photovoltaic fields from theoretical design to real fabrication [25,[27][28][29][30][31][32][33][34][35][36]. Subcells constituting the multi-junction cell are arranged in the order of decreasing the bandgap from the top where the thermal radiation is incident, and each subcell is monolithic interconnected by tunnel diodes. ...
... For a wider-bandgap top cell, we chose Ga In 1− As Sb 1− quaternary semiconductor of which electrical and optical properties can be tuned according to the and composition ratio. We permit the combination of and only when the lattice constant of Ga In 1− As Sb 1− , which is a function of and , is within 4.5% mismatch from that of an InAs considering methods to connect of lattice-mismatched materials, such as metamorphic [30,36], inverted metamorphic [27,28], and direct wafer bonding [29,31]. The ideal tunnel junction located between two subcells for the monolithic interconnection is assumed to be formed using 10-nm-thick -and -doped semiconductors of each subcell. ...
It is well known that performance of a thermophotovoltaic (TPV) device can be enhanced if the vacuum gap between the thermal emitter and the TPV cell becomes nanoscale due to the photon tunneling of evanescent waves. Having multiple bandgaps, multi-junction TPV cells have received attention as an alternative way to improve its performance by selectively absorbing the spectral radiation in each subcell. In this work, we comprehensively analyze the optimized near-field tandem TPV system consisting of the thin-ITO-covered tungsten emitter (at 1500 K) and GaInAsSb/InAs monolithic interconnected tandem TPV cell (at 300 K). We develop a simulation model by coupling the near-field radiation solved by fluctuational electrodynamics and the diffusion-recombination-based charge transport equations. The optimal configuration of the near-field tandem TPV system obtained by the genetic algorithm achieves the electrical power output of 8.41 W/cm$^2$ and the conversion efficiency of 35.6\% at the vacuum gap of 100 nm. We show that two resonance modes (i.e., surface plasmon polaritons supported by the ITO-vacuum interface and the confined waveguide mode in the tandem TPV cell) greatly contribute to the enhanced performance of the optimized system. We also show that the near-field tandem TPV system is superior to the single-cell-based near-field TPV system in both power output and conversion efficiency through loss analysis. Interestingly, the optimization performed with the objective function of the conversion efficiency leads to the current matching condition for the tandem TPV system regardless of the vacuum gap distances.
... The wafer bonding is mainly induced and dictated by hydrogen bridge bonds or van der Waals interactions, which are two orders of magnitude weaker than covalent bonds. In this sense, the electrically conductive bond layers should have very low surface roughness (<0.2 nm) and must be free from void [132]. As a major requirement, there should be a good chemical mechanical polishing step capable of forming two mirror surfaces, ideally they should be able to form compact bonding layer with higher bonding energy. ...
... Copyright 2018, Elsevier. (b) Typical wafer bonding process of a 2T GaInP/AlGaAs/Si triple junction tandem device [132]. (c) The comparison of inverted grown EX-8 and "upright grown" X-610 GaInP/ AlGaAs(GaAs)/Si triple junction solar cells [47]. ...
... All major steps involved in a SAB process are schematically illustrated in Figure 7(b), with the fabrication of GaInP/GaAs/Si TSCs as an example. Based on the schematic diagram of GaInP/GaAs/Si tandem device, Si, and GaAs wafers formed tandem structure when they were loaded on top and bottom electrodes into a bond chamber [132]. An argon fast atom beam was employed to remove the surface oxide, and no re oxidation occurred in the bonding layer under high vacuum ambient (<3 × 10 −8 mbar). ...
Due to stable and high power conversion efficiency (PCE), it is expected that silicon heterojunction (SHJ) solar cells will dominate the photovoltaic market. So far, the highest PCE of the SHJ-interdigitated back contact (IBC) solar cells has reached 26.7%, approximately approaching the theoretical Shockley–Queisser (SQ) limitation of 29.4%. To break through this limit, multijunction devices consisting of two or three stacked subcells have been developed, which can fully utilize the sunlight by absorbing different parts of the solar spectrum. This article provides a comprehensive overview of current research on SHJ-based tandem solar cells (SHJ-TSCs), including perovskite/SHJ TSCs and III–V/SHJ TSCs. Firstly, we give a brief introduction to the structures of SHJ-TSCs, followed by a discussion of fabrication processes. Afterwards, we focus on various materials and processes that have been explored to optimize the electrical and optical performance. Finally, we highlight the opportunities and challenges of SHJ-TSCs, as well as personal perspectives on the future development directions in this field.
... The two wafers are mechanically pressed, forming an almost uniform bonding area as shown in Figure 14 (a). Then, the upper substrate is removed, so far most successfully by complete chemical etching of the substrate [106,107,112,114,116], or by substrate lift-off after chemically etching a sacrificial layer (epitaxial lift-off or ELO) [117,118]. Other possibilities include ion implantation, laser-and stress-induced lift-off, which are common in other fields but less explored here [65]. ...
... In any case, a tunnel diode between Si and the first III-V subcell is still required, and is usually done on the III-V structures. With this wafer bonding strategy, Si-based 2J devices have reached 30.2% AM 1.5G efficiency [116], 30.0% under concentrated light [106], and 3J III-V bonded on Si have achieved 34.5% under AM 1.5G, the latter achieved very recently at the end of 2020 [92]. ...
As the photovoltaic sector approaches 1 TW in cumulative installed capacity, we provide an overview of the current challenges to achieve further technological improvements. On the raw materials side, we see no fundamental limitation to expansion in capacity of the current market technologies, even though basic estimates predict that the PV sector will become the largest consumer of Ag in the world after 2030. On the other hand, recent market data on PV costs indicates that the largest cost fraction is now infrastructure and area-related, and nearly independent of the core cell technology. Therefore, additional value adding is likely to proceed via an increase in energy yield metrics such as the power density and/or efficiency of the PV module. However, current market technologies are near their fundamental detailed balance efficiency limits. The transition to multijunction PV in tandem configurations is regarded as the most promising path to surpass this limitation and increase the power per unit area of PV modules. So far, each specific multijunction concept faces particular obstacles that have prevented their upscaling, but the field is rapidly improving. In this review work, we provide a global comparison between the different types of multijunction concepts, including III-Vs, Si-based tandems and the emergence of perovskite/Si devices. Coupled with analyses of new notable developments in the field, we discuss the challenges common to different multijunction cell architectures, and the specific challenges of each type of device, both on a cell level and on a module integration level. From the analysis, we conclude that several tandem concepts are nearing the disruption level where a breakthrough into mainstream PV is possible.
