scispace - formally typeset
Search or ask a question
Author

Keisuke Ohdaira

Bio: Keisuke Ohdaira is an academic researcher from Japan Advanced Institute of Science and Technology. The author has contributed to research in topics: Amorphous silicon & Crystalline silicon. The author has an hindex of 20, co-authored 177 publications receiving 1595 citations. Previous affiliations of Keisuke Ohdaira include Tohoku University & National Presto Industries.


Papers
More filters
Journal ArticleDOI
TL;DR: Explosive crystallization (EC) takes place during flash lamp annealing in micrometer-thick amorphous Si (a-Si) films deposited on glass substrates.
Abstract: Explosive crystallization (EC) takes place during flash lamp annealing in micrometer-thick amorphous Si (a-Si) films deposited on glass substrates. The EC starts from the edges of the a-Si films due to additional heating from flash lamp light. This is followed by lateral crystallization with a velocity on the order of m/s, leaving behind periodic microstructures in which regions containing several hundreds of nm-ordered grains and regions consisting of only 10-nm-sized fine grains alternatively appear. The formation of the dense grains can be understood as explosive solid-phase nucleation, whereas the several hundreds of nanometer-sized grains, stretched in the lateral direction, are probably formed through explosive liquid-phase epitaxy. This phenomenon will be applied to the high-throughput formation of thick poly-Si films for solar cells.

84 citations

Journal ArticleDOI
TL;DR: Subwavelength structure (SWS) was formed by simple wet chemical etching using catalysis of gold (Au) nanoparticle in this paper, where single nano-sized Au particle dispersion solution was coated onto silicon (Si) substrate with polished surface.

74 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used a-Si films to enhance the effective carrier lifetime of n-type crystalline Si (c-Si) wafers, and SiNx films are also essential for reducing surface recombination velocities to such low levels.
Abstract: Catalytic chemical vapor deposition (Cat-CVD), also called hot-wire CVD, yields silicon-nitride/amorphous-silicon (SiNx/a-Si) stacked layers with remarkably low surface recombination velocities (SRVs) of lower than 1.5 cm/s for n-type crystalline Si (c-Si) wafers, and lower than 9.0 cm/s for p-type wafers. The temperature throughout the formation of stacked layers is lower than 250 °C. The usage of a-Si films significantly enhances the effective carrier lifetime of c-Si wafers, and SiNx films are also essential for reducing SRVs to such low levels.

58 citations

Journal ArticleDOI
TL;DR: In this paper, flash lamp annealing of amorphous silicon (a-Si) films without thermal damage onto glass substrates was used for polycrystalline silicon formation.
Abstract: Polycrystalline silicon (poly-Si) films as thick as 4.5 µm are prepared by flash lamp annealing (FLA) of amorphous silicon (a-Si) films without thermal damage onto glass substrates. The a-Si films are deposited by catalytic chemical vapor deposition (Cat-CVD) at 320 °C. Since the hydrogen content in Cat-CVD a-Si films is as low as 3 at. %, they are easily converted to poly-Si without any dehydrogenation treatment. Chromium (Cr) films 60 nm thick are coated onto glass substrates to achieve high area uniformity of poly-Si formation. Secondary ion mass spectroscopy (SIMS) reveals that no diffused Cr atoms are detected inside poly-Si films and that crystallization is not the well-known metal-induced crystallization. Raman spectra from the poly-Si films show high crystallinity close to 1, and the photoluminescence (PL) spectrum demonstrates clear band-to-band transition, indicating the formation of device-quality poly-Si by FLA of Cat-CVD a-Si.

49 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: In this article, the use of black silicon (BSi) as an anti-reflection coating in solar cells is examined and appraised, based upon strategies towards higher efficiency renewable solar energy modules.
Abstract: Black silicon (BSi) represents a very active research area in renewable energy materials. The rise of BSi as a focus of study for its fundamental properties and potentially lucrative practical applications is shown by several recent results ranging from solar cells and light-emitting devices to antibacterial coatings and gas-sensors. In this paper, the common BSi fabrication techniques are first reviewed, including electrochemical HF etching, stain etching, metal-assisted chemical etching, reactive ion etching, laser irradiation and the molten salt Fray-Farthing-Chen-Cambridge (FFC-Cambridge) process. The utilization of BSi as an anti-reflection coating in solar cells is then critically examined and appraised, based upon strategies towards higher efficiency renewable solar energy modules. Methods of incorporating BSi in advanced solar cell architectures and the production of ultra-thin and flexible BSi wafers are also surveyed. Particular attention is given to routes leading to passivated BSi surfaces, which are essential for improving the electrical properties of any devices incorporating BSi, with a special focus on atomic layer deposition of Al2O3. Finally, three potential research directions worth exploring for practical solar cell applications are highlighted, namely, encapsulation effects, the development of micro-nano dual-scale BSi, and the incorporation of BSi into thin solar cells. It is intended that this paper will serve as a useful introduction to this novel material and its properties, and provide a general overview of recent progress in research currently being undertaken for renewable energy applications.

397 citations

Journal ArticleDOI
TL;DR: In this article, the authors fabricate and measure graded-index "black silicon" surfaces and find the underlying scaling law governing reflectance, which shows that as the density-grade depth increases, reflectance decreases exponentially with a characteristic grade depth of about 1/8 the vacuum wavelength or half the wavelength in Si.
Abstract: We fabricate and measure graded-index “black silicon” surfaces and find the underlying scaling law governing reflectance. Wet etching (100) silicon in HAuCl4, HF, and H2O2 produces Au nanoparticles that catalyze formation of a network of [100]-oriented nanopores. This network grades the near-surface optical constants and reduces reflectance to below 2% at wavelengths from 300 to 1000 nm. As the density-grade depth increases, reflectance decreases exponentially with a characteristic grade depth of about 1/8 the vacuum wavelength or half the wavelength in Si. Observation of Au nanoparticles at the ends of cylindrical nanopores confirms local catalytic action of moving Au nanoparticles.

347 citations

Journal ArticleDOI
TL;DR: The fundamentals of nanocrystal formation in plasmas are discussed, practical implementations of plasma reactors are reviewed, the materials that have been produced with nonthermal plAsmas and surface chemistries that have be developed are surveyed, and an overview of applications of plasma-synthesized nanocrystals is provided.
Abstract: Nonthermal plasmas have emerged as a viable synthesis technique for nanocrystal materials. Inherently solvent and ligand-free, nonthermal plasmas offer the ability to synthesize high purity nanocrystals of materials that require high synthesis temperatures. The nonequilibrium environment in nonthermal plasmas has a number of attractive attributes: energetic surface reactions selectively heat the nanoparticles to temperatures that can strongly exceed the gas temperature; charging of nanoparticles through plasma electrons reduces or eliminates nanoparticle agglomeration; and the large difference between the chemical potentials of the gaseous growth species and the species bound to the nanoparticle surfaces facilitates nanocrystal doping. This paper reviews the state of the art in nonthermal plasma synthesis of nanocrystals. It discusses the fundamentals of nanocrystal formation in plasmas, reviews practical implementations of plasma reactors, surveys the materials that have been produced with nonthermal pla...

292 citations

Journal ArticleDOI
TL;DR: In this paper, a critical review of the available literature is given to serve as a one-stop source for understanding the current status of potential-induced degradation (PID) research.
Abstract: Potential-induced degradation (PID) has received considerable attention in recent years due to its detrimental impact on photovoltaic (PV) module performance under field conditions. Both crystalline silicon (c-Si) and thin-film PV modules are susceptible to PID. While extensive studies have already been conducted in this area, the understanding of the PID phenomena is still incomplete and it remains a major problem in the PV industry. Herein, a critical review of the available literature is given to serve as a one-stop source for understanding the current status of PID research. This paper also aims to provide an overview of future research paths to address PID-related issues. This paper consists of three parts. In the first part, the modelling of leakage current paths in the module package is discussed. The PID mechanisms in both c-Si and thin-film PV modules are also comprehensively reviewed. The second part summarizes various test methods to evaluate PV modules for PID. The last part focuses on studies related to PID in the omnipresent p-type c-Si PV modules. The dependence of temperature, humidity and voltage on the progression of PID is examined. Preventive measures against PID at the cell, module and system levels are illustrated. Moreover, PID recovery in standard p-type c-Si PV modules is also studied. Most of the findings from p-type c-Si PV modules are also applicable to other PV module technologies.

288 citations

Journal ArticleDOI
15 Apr 2020-Joule
TL;DR: In this article, a solution-based blading of perovskites onto silicon wafers textured with pyramids less than 1μm in height is proposed, which is rough enough to scatter light within the silicon nearly as efficiently as large pyramids but smooth enough to solution-process a perovskiite film.

254 citations