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 this paper, we present our latest results toward high-efficiency thin-film silicon solar cells. Owing to the superior light trapping capability of periodic textures combined with other technologies, a new world record was achieved for the efficiency of single-junction microcrystalline silicon solar cells, with a conversion efficiency of 11.0%, independently confirmed by the Advanced Industrial Science and Technology (AIST) Characterization, Standards, and Measurement (CSM) team.

11.0%-Efficient Thin-Film Microcrystalline Silicon Solar Cells With Honeycomb Textured Substrates

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

We numerically investigate broadband optical absorption enhancement in thin, 400-nm thick microcrystalline silicon (µc-Si) photovoltaic devices by photonic crystals (PCs). We realize absorption enhancement by coupling the light from the free space to the large area resonant modes at the photonic band-edge induced by the photonic crystals. We show that multiple photonic band-edge modes can be produced by higher order modes in the vertical direction of the Si photovoltaic layer, which can enhance the absorption on multiple wavelengths. Moreover, we reveal that the photonic superlattice structure can produce more photonic band-edge modes that lead to further optical absorption. The absorption average in wavelengths of 500-1000 nm weighted to the solar spectrum (AM 1.5) increases almost twice: from 33% without photonic crystal to 58% with a 4 × 4 period superlattice photonic crystal; our result outperforms the Lambertian textured structure.

Enhancement of broadband optical absorption in photovoltaic devices by band-edge effect of photonic crystals

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 carry out the structural design of photonic crystals to enhance the optical absorption of thin-film microcrystalline silicon (μc-Si) solar cells using two methods. First, by exhaustive search, we choose a structure with the largest absorption within the investigated patterns. Then we employ a sensitivity analysis to finely modulate the structure for further increase of the optical absorption. The obtained μc-Si solar cell structure with a photonic crystal in this work has more than twice as much optical absorption as that without a photonic crystal.

Structural Optimization of Photonic Crystals for Enhancing Optical Absorption of Thin Film Silicon Solar Cell Structures

Abstract We establish an invariance principle corresponding to the universality of random matrices. More precisely, we prove the dynamical universality of random matrices in the sense that, if the random point fields $$ \mu ^N $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>μ</mml:mi> <mml:mi>N</mml:mi> </mml:msup> </mml:math> of N -particle systems describing the eigenvalues of random matrices or log-gases with general self-interaction potentials V converge to some random point field $$ \mu $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>μ</mml:mi> </mml:math> , then the associated natural $$ \mu ^N $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mi>μ</mml:mi> <mml:mi>N</mml:mi> </mml:msup> </mml:math> -reversible diffusions represented by solutions of stochastic differential equations (SDEs) converge to some $$ \mu $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>μ</mml:mi> </mml:math> -reversible diffusion given by the solution of an infinite-dimensional SDE (ISDE). Our results are general theorems that can be applied to various random point fields related to random matrices such as sine, Airy, Bessel, and Ginibre random point fields. In general, the representations of finite-dimensional SDEs describing N -particle systems are very complicated. Nevertheless, the limit ISDE has a simple and universal representation that depends on a class of random matrices appearing in the bulk, and at the soft- and at hard-edge positions. Thus, we prove that ISDEs such as the infinite-dimensional Dyson model and the Airy, Bessel, and Ginibre interacting Brownian motions are universal dynamical objects. 

/pdf/dynamical-universality-for-random-matrices-sxexcvjd.pdf

Yosuke Kawamoto

Papers

Enhancement of broadband optical absorption in photovoltaic devices by band-edge effect of photonic crystals

Photonic crystal microcrystalline silicon solar cells

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

Structural Optimization of Photonic Crystals for Enhancing Optical Absorption of Thin Film Silicon Solar Cell Structures

Dynamical universality for random matrices