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The development of high-performance solar cells offers a promising pathway toward achieving high power per unit cost for many applications. As single-junction solar cells are limited to 30-32% conversion efficiency under 1-sun, multi-junction or tandem solar cells are expected to contribute to higher performances. The II-VI compound, chalcopyrite, and kesterite-based tandem solar cells are expected as high-efficiency and low-cost solar cells. This paper presents analytical results for efficiency potential and loss elements of II-VI compound, chalcopyrite, and kesterite-based tandem solar cells. The 2-junction and 3-junction tandem solar cells have potential efficiencies of 36% and 42%, respectively, by improving external radiative efficiency and reducing resistance and optical losses. Some paths for improving efficiencies of tandem solar cells are shown by analyzing their loss elements. Optimization of band-gap energy of sub-cells and photon recycling are also recommended.

Multijunction (MJ) solar cells haveattracted attention as next-generation solar cells. In particular, III-V-based MJ solar cells connected with heterogeneous cells, such as GaAs//Si and GaAs//CIGSe (CuIn 1−y Ga y Se 2 ), are expected to be highly efficient and low cost. In this article, we demonstrate a highly efficient InGaP/Al 0.06 Ga 0.94 As//CIGSe three-junction solar cell. The key technology used to fabricate this solar cell is a bonding method that uses a Pd nanoparticle array and an adhesive material (silicone adhesive) for the bonding interface, which is modified for our previous ""smart stack"" technology. This modified smart stack technology contributes to enhancing the bonding strength between the GaAs-based cell and the CIGSe cell. Using this technology, total efficiency of 28.06% was attained, as certified by the National Institute of Advanced Industrial Science and Technology. This value is superior to that obtained in our previous result (27.2%) and represents the highest efficiency ever reported for two-terminal GaAs//CIGSe-based tandem solar cells.

8th World Conference on Photovoltaic Energy Conversion; 270-272, Multijunction (MJ) solar cells achieve very high efficiencies by effectively utilizing the solar spectrum. Previously, we constructed a GaAs//CuIn1-yGaySe2 (CIGSe) MJ solar cell using a unique mechanical stacking technology with Pd nanoparticle and silicone adhesive at the bonding interface (modified smart stack technology). The modified smart stack was developed to increase the bonding strength of the GaAs//CIGSe interface. The efficiency of 28.06% with a InGaP/AlGaAs//CIGSe three-junction solar cell was the best value among GaAs//CIGSe tandem solar cells as two-terminal. In this report, we fabricated a flexible InGaP/AlGaAs//Cu(In1-x,Gax)(Sy,Se1-y)2 (CIGSSe) threejunction solar cell using a flexible CIGSSe bottom cell. Appling the modified smart stack, the total efficiency with 24.3% for aperture area (26.7% for active area) was realized under the global standard AM1.5G spectrum. This is the first demonstration as a flexible GaAs//CIGSe-based MJ solar cell. The superior performance can be achieved by improving the reflection loss at the bonding interface. We predict that the efficiency could be boosted to 35% by minimizing the thickness of transparent conducting oxide layer and the surface roughness of CIGSSe cell. The results demonstrate the potential of GaAs//CIGSe-based MJ solar cell as next-generation solar cells for application such as vehicle-integrated photovoltaics.

Multijunction (MJ) solar cells achieve high efficiencies by effectively utilizing the solar spectrum. Previously, we have developed III-V MJ solar cells using smart stack technology, a mechanical stacking technology that uses a Pd nanoparticle array. In this study, we fabricated an InGaP/AlGaAs//CuxIn1−yGaySe2 three-junction solar cell by applying modified smart stack technology with a Pd nanoparticle array and adhesive material. Using adhesive material (silicone adhesive), the bonding stability was improved conspicuously. The total efficiency achieved was 27.2% under AM 1.5 G solar spectrum illumination, which is a better performance compared to our previous result (24.2%) for a two-terminal solar cell. The performance was achieved by optimizing the structure of the upper GaAs-based cell and by using a CuxIn1−yGaySe2 solar cell with a specialized performance for an MJ configuration. In addition, we assessed the reliability of the InGaP/AlGaAs//CuxIn1−yGaySe2 three-junction solar cell through a heat cycle test (from −40°C to +85°C; 50 cycles) and were able to confirm that our solar cells show high resistivity under severe conditions. The results demonstrate the potential of III-V//CuxIn1−yGaySe2 MJ solar cells as next-generation photovoltaic cells for applications such as vehicle-integrated photovoltaics; they also demonstrate the effectiveness of modified smart stack technology in fabricating MJ cells.

In order to realize a clean energy society by using renewable energies, high-performance solar cells are a very attractive proposition. The development of high-performance solar cells offers a promising pathway toward achieving high power per unit cost for many applications. As state-of-the-art of single-junction solar cells are approaching the Shockley-Queisser limit of 32%-33%, an important strategy to raise the efficiency of solar cells further is stacking solar cell materials with different bandgaps to absorb different colors of the solar spectrum. The III-V semiconductor materials provide a relatively convenient system for fabricating multi-junction solar cells providing semiconductor materials that effectively span the solar spectrum as demonstrated by world record efficiencies (39.2% under one-sun and 47.1% under concentration) for six-junction solar cells. This success has inspired attempts to achieve the same with other materials like perovskites for which lower manufacturing costs may be achieved. Recently, Si multi-junction solar cells such as III-V/Si, II-VI/Si, chalcopyrite/Si, and perovskite/Si have become popular and are getting closer to economic competitiveness. Here, we discuss the perspectives of multi-junction solar cells from the viewpoint of efficiency and low-cost potential based on scientific and technological arguments and possible market applications. In addition, this article provides a brief overview of recent developments with respect to III-V multi-junction solar cells, III-V/Si, II-VI/Si, perovskite/Si tandem solar cells, and some new ideas including so-called 3rd generation concepts.

Low-defect III-V multilayer structures grown on Si(100) open opportunities for a wide range of cost-effective high-performance photovoltaic and optoelectronic devices. For that, (Al)GaP epilayers prepared almost lattice-matched on Si(100) substrates can serve as high-quality virtual substrates for subsequent heteroepitaxial growth. The evolution of crystal defects, such as stacking fault pyramids or threading dislocations, needs to be impeded already during the first preparation step, the III-V-on-Si nucleation, as they tend to propagate into the subsequently grown layers and increase nonradiative electron-hole recombination rates, which finally degrade the device performance. We establish a ternary GaP/AlP pulsed nucleation process on Si(100) substrates fabricated by metalorganic chemical vapor deposition, and compare it to the defect evolution from pure GaP nucleation layers (NLs). The entire procedure was optically monitored in situ using reflection anisotropy spectroscopy. Crystal defects were investigated by electron channeling contrast imaging. GaP grown on GaP/AlP NLs exhibits drastically reduced densities of threading dislocations and stacking faults by 1 and 2 orders of magnitude, respectively, compared to buffer layers grown on binary GaP NLs. We observed that the surface morphology at the initial stage of growth of these buffer layers is significantly smoother compared to the buffer layers grown on pure GaP NLs using atomic force microscopy. The proposed nucleation procedure here is supposed to substantially improve the crystalline quality of III-V buffer layers integrated on Si(100) wafers.

A thin-film GaAs/AlGaAs rear-heterojunction photonic power converter with a back reflector is presented by Henning Helmers and co-workers in article number 2100113. Photon recycling is leveraged to increase the excess carrier density and consequently the output voltage. Optical resonance yields highest absorptance for near-bandgap photons. Thereby thermalization losses are minimized without compromising minimal transmission. A photovoltaic conversion efficiency of 68.9% for 858 nm monochromatic light is demonstrated.

Over the past decade, the global cumulative installed photovoltaic (PV) capacity has grown exponentially, reaching 591 GW in 2019. Rapid progress was driven in large part by improvements in solar cell and module efficiencies, reduction in manufacturing costs and the realization of levelized costs of electricity that are now generally less than other energy sources and approaching similar costs with storage included. Given this success, it is a particularly fitting time to assess the state of the photovoltaics field and the technology milestones that must be achieved to maximize future impact and forward momentum. This roadmap outlines the critical areas of development in all of the major PV conversion technologies, advances needed to enable terawatt-scale PV installation, and cross-cutting topics on reliability, characterization, and applications. Each perspective provides a status update, summarizes the limiting immediate and long-term technical challenges and highlights breakthroughs that are needed to address them. In total, this roadmap is intended to guide researchers, funding agencies and industry in identifying the areas of development that will have the most impact on PV technology in the upcoming years.

37th European Photovoltaic Solar Energy Conference and Exhibition; 574-578, Triple-junction solar cells with top cells made from III-V compound semiconductors on a silicon bottom cell show conversion efficiencies beyond the theoretical limit of single-junction devices, so this is one of the promising technologies for terrestrial photovoltaics. In this work, a III-V//Si tandem device with 34.5% efficiency is presented and further developments are discussed. A detailed investigation of the silicon bottom cell revealed, that with optimum wafer resistivity (~1 Ω cm) and low-temperature passivation of the cell perimeter, the perimeter losses can be reduced to ~0.2%abs. This corresponds to an efficiency gain of up to 0.8%abs for the current devices.

The bulk minority carrier lifetime and interface recombination velocity in GaInP double-heterostructures (DHs) lattice matched to GaAs are extracted using time-resolved photoluminescence (PL) measured between 300 and 500K. Effective lifetimes show a strong dependence on temperature for samples with insufficiently strong confinement potentials due to significant thermionic emission losses out of the DHs. An increased PL signal from the underlying GaAs layer relative to GaInP's PL at high temperatures supports this hypothesis. The impact is a shorter recombination lifetime which can be wrongly interpreted as a high interface recombination velocity of up to 4500 cm/s at 500K. These effects are investigated experimentally using samples of different barrier heights based on the Al-content in (AlxGa1-x)0.51In0.49P. A larger barrier height is shown to inhibit thermionic emission out of the DH, thus revealing a more accurate interface recombination velocity of 300 cm/s at 500K. The results are then used to develop a correction procedure to extract a more accurate interface recombination velocity at the barriers of the DH. Optoelectronic device simulations are used to gain insight into carrier dynamics as a function of temperature and the DH's barrier height, and confirm a strong inhibition of the thermionic emission losses as the Al-content is maximized in the barrier.

The terrestrial photovoltaic market is dominated by single‐junction silicon solar cell technology. However, there is a fundamental efficiency limit at 29.4%. This is overcome by multijunction devices. Recently, a GaInP/GaAs//Si wafer‐bonded triple‐junction two‐terminal device is presented with a 33.3% (AM1.5g) efficiency. Herein, it is analyzed how this device is improved to reach a conversion efficiency of 34.1%. By improving the current matching, an efficiency of 35% (two terminals, AM1.5g) is expected.

37th European Photovoltaic Solar Energy Conference and Exhibition; 1984-1994, The dominating solar cell technology for PV power plants is the Si based solar cell. However, solar cell technologies such as chalcogenide, organic, III-V or perovskite solar cells, all have their own niche markets or potentials. The aim of this work is to provide an overview and comparison of the different solar cell technologies for the application in integrated photovoltaics. The current statuses of the technologies are reviewed. Characteristics relevant for integrated photovoltaics are defined and each technology is discussed regarding those key influencing factors. The results of the comparison are compiled in a concise table summarizing strengths and weaknesses of the different technologies in respect of their application for integrated photovoltaics.

In this work, we propose and realize three different design strategies to implement an optical cavity in GaAs thin film solar cells in order to confine its internal luminescence and hence to exploit photon recycling. The strategies are based on the definition of a highly reflective and very conductive back side, whereas front side light extraction is limited by total internal reflection. We show characterization results on the internal reflectivity of the back reflector and on the contact resistance at the rear side, important quantities for a good functioning of the final solar cell. First, a back side using only metal was optimized with a pure Ag layer leading to an internal reflectivity of 95.2% and a contact resistance of 1.0 × 10−4 O for a 1 cm2 device. With a metal‐dielectric stack at the back side and electrical contacts made by metals via point‐contacts, a second approach led to averaged internal reflectivity of 98.0% and contact resistance of 1.8 × 10−4 O for a 1 cm2 device. A third strategy in which a transparent conductive oxide in combination with a metal layer was used did not show the expected results in optical and electrical properties. We fabricated and characterized solar cells with the most promising back sides. When comparing with an ordinary reference GaAs solar cell, external radiative efficiency increased by factors of 150% and 90% for the thin film solar cells with pure Ag and with the metal‐dielectric stack at the back side, allowing enhancements of 19 and 13 mV in VOC, respectively.

In the version of this Article originally published, in the 'Rear-side light trapping' paragraph of the Methods section, the values of depth and fill factor were incorrectly given as 350 nm and 50%, respectively; instead, the values should have read 250 nm and 60%. This has now been corrected.