Photovoltaic (PV) conversion of solar energy starts to give an appreciable contribution to power generation in many countries, with more than 90% of the global PV market relying on solar cells base...

https://www.tandfonline.com/doi/pdf/10.1080/23746149.2018.1548305

Silicon solar cells: toward the efficiency limits

High-speed, high-efficiency photodetectors play an important role in optical communication links that are increasingly being used in data centres to handle higher volumes of data traffic and higher bandwidths, as big data and cloud computing continue to grow exponentially. Monolithic integration of optical components with signal-processing electronics on a single silicon chip is of paramount importance in the drive to reduce cost and improve performance. We report the first demonstration of micro- and nanoscale holes enabling light trapping in a silicon photodiode, which exhibits an ultrafast impulse response (full-width at half-maximum) of 30 ps and a high efficiency of more than 50%, for use in data-centre optical communications. The photodiode uses micro- and nanostructured holes to enhance, by an order of magnitude, the absorption efficiency of a thin intrinsic layer of less than 2 µm thickness and is designed for a data rate of 20 gigabits per second or higher at a wavelength of 850 nm. Further optimization can improve the efficiency to more than 70%. Light-trapping nanoscale holes are exploited to improve the speed and efficiency of silicon photodiodes with intrinsic layers less than 2 μm thick.

Photon-trapping microstructures enable high-speed high-efficiency silicon photodiodes

In the current study, the nonlinear radiative heat transfer effects due to solar radiation in magneto-hydrodynamic (MHD) nanofluidic problem are analyzed effectively by novel application of numerical computing by Adams predictor–corrector and explicit backward difference solvers. The governing relations of PDEs for the model are transformed into the system of ODEs, and numerical solvers are applied to the transformed system to study the effect of radiation parameter along with thermophoresis parameter, Brownian motion parameter, magnetic field parameter, Lewis number, Prandtl number, Eckert number and Biot number on velocity, temperature and nanoparticle concentration profiles. The comparative study of both solvers is provided in sufficient number of graphical and numerical illustrations to prove the worth in terms of accuracy, robustness and stability.

Numerical Treatments to Analyze the Nonlinear Radiative Heat Transfer in MHD Nanofluid Flow with Solar Energy

The present status of R&D for various types of solar cells is presented by overviewing research and development projects for solar cells in Japan as the PV R&D Project Leader of the New Energy and Industrial Technology Development Organization (NEDO) and the Japan Science and Technology Agency (JST). Developments of high-efficiency solar cells such as 44.4% (under concentration) and 37.9% (under 1-sun) InGaP/GaAs/InGaAs 3-junction solar cells by Sharp, 26.6% crystalline Si heterojunction back-contact (HBC) solar cells by Kaneka, 22.3% CIGS solar cells by Solar Frontier have been demonstrated under the NEDO PV R&D Project. 15.0% efficiency has also been attained with 1 cm2 perovskite solar cell by NIMS under the JST Project. This article also presents analytical results for efficiency potential of high-efficiency solar cells based on external radiative efficiency (ERE), open-circuit voltage loss and fill factor loss. Crystalline Si solar cells, GaAs, III–V compound 3-junction and 5-junction, CIGSe, and CdTe solar cells have efficiency potential of 28.5%, 29.7%, 42%, 43%, 26.5%, and 26.5% under 1-sun condition, respectively, by improvements in ERE.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/580E344EDB972224FF62CA1977747415/S0884291417003351a.pdf/div-class-title-efficiency-potential-and-recent-activities-of-high-efficiency-solar-cells-div.pdf

Efficiency potential and recent activities of high-efficiency solar cells

With the objective to conceive a plasmonic solar cell with enhanced photocurrent, we investigate the role of plasmonic nanoshells, embedded within a ultrathin microcrystalline silicon solar cell, in enhancing broadband light trapping capability of the cell and, at the same time, to reduce the parasitic loss. The thickness of the considered microcrystalline silicon (μc-Si) layer is only ~1/6 of conventional μc-Si based solar cells while the plasmonic nanoshells are formed by a combination of silica and gold, respectively core and shell. We analyze the cell optical response by varying both the geometrical and optical parameters of the overall device. In particular, the nanoshells core radius and metal thickness, the periodicity, the incident angle of the solar radiation and its wavelength are varied in the widest meaningful ranges. We further explain the reason for the absorption enhancement by calculating the electric field distribution associated to resonances of the device. We argue that both Fabry-Perot-like and localized plasmon modes play an important role in this regard.

/pdf/broadband-absorption-enhancement-in-plasmonic-nanoshells-3h2h3le02q.pdf

Broadband absorption enhancement in plasmonic nanoshells-based ultrathin microcrystalline-Si solar cells

Enhancing the absorption of thin-film microcrystalline silicon solar cells over a broadband range in order to improve the energy conversion efficiency is a very important challenge in the development of low cost and stable solar energy harvesting. Here, we demonstrate that a broadband enhancement of the absorption can be achieved by creating a large number of resonant modes associated with two-dimensional photonic crystal band edges. We utilize higher-order optical modes perpendicular to the silicon layer, as well as the band-folding effect by employing photonic crystal superlattice structures. We establish a method to incorporate photonic crystal structures into thin-film (~500 nm) microcrystalline silicon photovoltaic layers while suppressing undesired defects formed in the microcrystalline silicon. The fabricated solar cells exhibit 1.3 times increase of a short circuit current density (from 15.0 mA/cm2 to 19.6 mA/cm2) by introducing the photonic crystal structure, and consequently the conversion efficiency increases from 5.6% to 6.8%. Moreover, we theoretically analyze the absorption characteristics in the fabricated cell structure, and reveal that the energy conversion efficiency can be increased beyond 9.5% in a structure less than 1/400 as thick as conventional crystalline silicon solar cells with an efficiency of 24%. © 2015 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.

/pdf/photonic-crystal-microcrystalline-silicon-solar-cells-4hkyen4wpq.pdf

Photonic crystal microcrystalline silicon solar cells

We investigate the improvement of the conversion efficiency of ultra-thin (~500nm-thick) microcrystalline silicon (μc-Si) solar cells incorporating photonic-crystal structures, where light absorption is strongly enhanced by the multiple resonant modes in the photonic crystal. We focus on the quality of the intrinsic μc-Si layer deposited on the substrate, which is structured to form a photonic crystal at its upper surface with a period of several hundred nanometers. We first study the crystalline quality from the viewpoint of the crystalline fraction and show that the efficiency can be improved when the deposition conditions for the μc-Si layer are tuned to give an almost constant crystalline fraction of ~50% across the entire film. We then study the influence of the photonic-crystal structure on the crystalline quality. From transmission-electron microscope images, we show that the collision of μc-Si grains growing at different angles occurs when a photonic-crystal structure with an angular surface is used; this can be suppressed by introducing a rounded surface structure. As a result, we demonstrate an efficiency of 8.7% in a ~500-nm thick, homo-junction μc-Si solar cell, which has only ~1/4 the thickness of typical μc-Si solar cells. We also discuss the possibility of further improving the efficiency by performing calculations that focus on the absorption characteristics of the fabricated cell structure.

Improved efficiency of ultra-thin µc-Si solar cells with photonic-crystal structures.

We investigate microcrystalline-silicon (μc-Si) solar cells with photonic crystals on the top surface, which exploit the large-area resonant effect in photonic crystals to enhance light absorption, for the first time. Guidelines for designing the surface photonic crystals are discussed, showing the importance of oblique leakage loss suppression. The influence of direct surface etching of the intrinsic μc-Si layer (or photovoltaic layer) is studied, and it is shown that unbalanced etching of the amorphous and crystalline components of the μc-Si layer deteriorates the electronic performance, in particular, the open-circuit voltage and fill factor. We then introduce photonic crystals under an adequate etching condition, and confirm that the light absorption (or the external quantum efficiency) is successfully enhanced by improving the incident light coupling to the resonant modes. Finally, we fabricate a few-micrometer-thick μc-Si solar cell with a photonic crystal on the top surface and demonstrate an active-area efficiency of 11%, resulting from enhancement of the short-circuit current density, while simultaneously suppressing the deterioration of open-circuit voltage and fill factor. The obtained efficiency is the highest reported for a category of μc-Si solar-cell in which all the n/i/p layers are composed of Si, excluding wide-gap materials such as silicon oxide.

Microcrystalline-Silicon Solar Cells With Photonic Crystals on the Top Surface

We investigate the enhancement of optical absorption in thin-film microcrystalline silicon solar cell by creating multiple resonant modes based on photonic crystal band-edge effect. Experimentally, 1.3 times increase of photo-current is observed, and theoretically it is shown that ultimately more than 9.6% conversion efficiency could be possible even with only “500nm” microcrystalline silicon with indirect electronic gap.

Takami Umeda

Papers

Photonic crystal microcrystalline silicon solar cells

Improved efficiency of ultra-thin µc-Si solar cells with photonic-crystal structures.

Microcrystalline-Silicon Solar Cells With Photonic Crystals on the Top Surface

Microcrystalline silicon solar cells with photonic crystals