Photovoltaic (PV) technology offers an economic and sustainable solution to the challenge of increasing energy demand in times of global warming. The world PV market is currently dominated by the ...homo-junction crystalline silicon (c-Si) PV technology based on high temperature diffused p-n junctions, featuring a low power conversion efficiency (PCE). Recent years have seen the successful development of Si heterojunction technologies, boosting the PCE of c-Si solar cells over 26%. This article reviews the development status of high-efficiency c-Si heterojunction solar cells, from the materials to devices, mainly including hydrogenated amorphous silicon (a-Si:H) based silicon heterojunction technology, polycrystalline silicon (poly-Si) based carrier selective passivating contact technology, metal compounds and organic materials based dopant-free passivating contact technology. The application of silicon heterojunction solar cells for ultra-high efficiency perovskite/c-Si and III-V/c-Si tandem devices is also reviewed. In the last, the perspective, challenge and potential solutions of silicon heterojunction solar cells, as well as the tandem solar cells are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Nitride materials feature strong chemical bonding character that leads to unique crystal structures, but many ternary nitride chemical spaces remain experimentally unexplored. The search for ...previously undiscovered ternary nitrides is also an opportunity to explore unique materials properties, such as transitions between cation-ordered and -disordered structures, as well as to identify candidate materials for optoelectronic applications. Here, we present a comprehensive experimental study of MgSnN2, an emerging II–IV–N2 compound, for the first time mapping phase composition and crystal structure, and examining its optoelectronic properties computationally and experimentally. We demonstrate combinatorial cosputtering of cation-disordered, wurtzite-type MgSnN2 across a range of cation compositions and temperatures, as well as the unexpected formation of a secondary, rocksalt-type phase of MgSnN2 at Mg-rich compositions and low temperatures. A computational structure search shows that the rocksalt-type phase is substantially metastable (>70 meV/atom) compared to the wurtzite-type ground state. Spectroscopic ellipsometry reveals optical absorption onsets around 2 eV, consistent with band gap tuning via cation disorder. Finally, we demonstrate epitaxial growth of a mixed wurtzite-rocksalt MgSnN2 on GaN, highlighting an opportunity for polymorphic control via epitaxy. Collectively, these findings lay the groundwork for further exploration of MgSnN2 as a model ternary nitride, with controlled polymorphism, and for device applications, enabled by control of optoelectronic properties via cation ordering.
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IJS, KILJ, NUK, PNG, UL, UM
Ultra-thin photovoltaics offer the potential for increasing efficiency while minimizing costs. However, a suitable light trapping strategy is needed to reach the optically thick regime for otherwise ...thin-film structures. III-V materials can benefit from simple adjacent light trapping structures, if correctly designed. Here we present three strategies for a 300 nm thick GaAs cell using front photonic crystals, back photonic crystals, and both front and back combined, predicting a maximum photocurrent, J
=29.9 mA/cm
under the radiative limit, including an enhanced absorption in the Urbach-tail. We analyze the increased absorption isolating the Fabry-Perot resonances, the single pass absorption and the scattered contribution from the incident light.
Inorganic nitrides with wurtzite crystal structures are well-known semiconductors used in optical and electronic devices. In contrast, rocksalt-structured nitrides are known for their superconducting ...and refractory properties. Breaking this dichotomy, herewe report ternary nitride semiconductors with rocksalt crystal structures, remarkable electronic properties, and the general chemical formula MgₓTM
1−xN (TM = Ti, Zr, Hf, Nb). Our experiments show that these materials form over a broad metal composition range, and that Mg-rich compositions are nondegenerate semiconductors with visible-range optical absorption onsets (1.8 to 2.1 eV) and up to 100 cm² V−1·s−1 electron mobility for MgZrN₂ grown on MgO substrates. Complementary ab initio calculations reveal that these materials have disorder-tunable optical absorption, large dielectric constants, and electronic bandgaps that are relatively insensitive to disorder. These ternary MgₓTM
1−xN semiconductors are also structurally compatible both with binary TMN superconductors and main-group nitride semiconductors along certain crystallographic orientations. Overall, these results highlight MgₓTM
1−xN as a class of materials combining the semiconducting properties of main-group wurtzite nitrides and rocksalt structure of superconducting transition-metal nitrides.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
The opportunity for enhanced functional properties in semiconductor solid solutions has attracted vast scientific interest for a variety of novel applications. However, the functional versatility ...originating from the additional degrees of freedom due to atomic composition and ordering comes along with new challenges in characterization and modeling. Developing predictive synthesis–structure–property relationships is prerequisite for effective materials design strategies. Here, a first‐principles based model for property prediction in such complex semiconductor materials is presented. This framework incorporates nonequilibrium synthesis, dopants and defects, and the change of the electronic structure with composition and short range order. This approach is applied to ZnSnN2 (ZTN) which has attracted recent interest for photovoltaics. The unintentional oxygen incorporation and its correlation with the cation stoichiometry leads to the formation of a solid solution with dual sublattice mixing. A nonmonotonic doping behavior as a function of the composition is uncovered. The degenerate doping of near‐stoichiometric ZTN, which is detrimental for potential applications, can be lowered into the 1017 cm−3 range in highly off‐stoichiometric material, in quantitative agreement with experiments.
A predictive synthesis–structure–property model from first principles is presented for nonideal semiconductor solid solutions, accounting for off‐stoichiometry, impurities, disorder, and metastability. This model elucidates the mysterious nonmonotonic doping as a function of oxygen content in ZnSnN2, a promising photovoltaic material. The key lies in the formation of a dual sublattice mixed solid solution.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The opportunity for enhanced functional properties in semiconductor solid solutions has attracted vast scientific interest for a variety of novel applications. However, the functional versatility ...originating from the additional degrees of freedom due to atomic composition and ordering comes along with new challenges in characterization and modeling. Developing predictive synthesis-structure-property relationships is prerequisite for effective materials design strategies. Here, a first-principles based model for property prediction in such complex semiconductor materials is presented. This framework incorporates nonequilibrium synthesis, dopants and defects, and the change of the electronic structure with composition and short range order. This approach is applied to ZnSnN
(ZTN) which has attracted recent interest for photovoltaics. The unintentional oxygen incorporation and its correlation with the cation stoichiometry leads to the formation of a solid solution with dual sublattice mixing. A nonmonotonic doping behavior as a function of the composition is uncovered. The degenerate doping of near-stoichiometric ZTN, which is detrimental for potential applications, can be lowered into the 10
cm
range in highly off-stoichiometric material, in quantitative agreement with experiments.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Recently theorized hybrid II-IV-N2/III-N heterostructures, based on current commercialized (In,Ga)N devices, are predicted to significantly advance the design space of highly efficient ...optoelectronics in the visible spectrum, yet there are few epitaxial studies of II-IV-N2 materials. In this work, we present heteroepitaxial ZnGeN2 grown on GaN buffers and AlN templates. We demonstrate that a GaN nucleating surface is crucial for increasing the ZnGeN2 crystallization rate to combat Zn desorption, extending the stoichiometric growth window from 215 °C on AlN to 500 °C on GaN buffers. Structural characterization reveals well-crystallized films with threading dislocations extending from the GaN buffer. These films have a critical thickness for relaxation of 20–25 nm as determined by reflection high energy electron diffraction (RHEED) and cross-sectional scanning electron microscopy (SEM). The films exhibit a cation-disordered wurtzite structure, with lattice constants a = 3.216 ± 0.004 Å and c = 5.215 ± 0.005 Å determined by RHEED and X-ray diffraction (XRD). This work demonstrates a significant step toward the development of hybrid ZnGeN2-GaN integrated devices.
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II-IV-V
2
materials offer the promise of enhanced functionality in optoelectronic devices due to their rich ternary chemistry. In this review, we consider the potential for new optoelectronic devices ...based on nitride, phosphide, and arsenide II-IV-V
2
materials. As ternary analogs to the III-V materials, these compounds share many of the attractive features that have made the III-Vs the basis of modern optoelectronic devices (
e.g.
high mobility, strong optical absorption). Control of cation order parameter in the II-IV-V
2
materials can produce significant changes in optoelectronic properties at fixed chemical composition, including decoupling band gap from lattice parameter. Recent progress has begun to resolve outstanding questions concerning the structure, dopability, and optical properties of the II-IV-V
2
materials. Remaining research challenges include growth optimization and integration into heterostructures and devices.
II-IV-V
2
materials offer the promise of enhanced functionality in optoelectronic devices due to their rich ternary chemistry.
As the world’s demand for energy grows, the search for cost competitive and earth abundant thin film photovoltaic absorbers is becoming increasingly important. A promising approach to tackle this ...challenge is through thin film photovoltaics made of elements that are abundant in the Earth’s crust. In this work, we focus on Cu2SnS3, a promising earth abundant absorber material. Recent publications have presented 3% and 6% device efficiencies using Cu2SnS3-based absorber materials and alloys, respectively. However, little is understood about the fundamental defect and doping physics of this material, which is needed for further improvements in device performance. Here, we identify the origins of the changes in doping in sputtered cubic Cu2SnS3 thin films using combinatorial experiments and first-principles theory. Experimentally, we find that the cubic Cu2SnS3 has a large phase width and that the electrical conductivity increases with increasing Cu and S content in the films, which cannot be fully explained by the theoretical point defect model. Instead, theoretical calcuations suggest that under Cu-rich conditions alloying with an isostructural metallic Cu3SnS4 phase occurs, causing high levels of p-type doping; this theory is consistent with experimental Raman and NEXAFS spectroscopy data. These experimental and theoretical works lead to the conclusion that Cu2SnS3 films must be grown both S-poor and Cu-poor in order to achieve moderate hole concentrations. These new insights enable the design of growth processes that target the desired carrier concentrations for solar cell fabrication. Using the strategies described above, we have been able to tune the carrier concentration over >3 orders of magnitude and achieve films with p-type doping of ≤1018 cm–3, facilitating future device integration of these films.
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10.
The 2020 photovoltaic technologies roadmap Wilson, Gregory M; Al-Jassim, Mowafak; Metzger, Wyatt K ...
Journal of physics. D, Applied physics,
12/2020, Volume:
53, Issue:
49
Journal Article
Peer reviewed
Open access
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.
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