Single Crystal Si Solar Cells Research Articles

The effects of Ag particle morphology on the antireflective properties of silicon textured using Ag-assisted chemical etching

Metal assisted chemical etching (MaCE) of silicon wafers is of interest for fabrication of antireflective layers for single-crystal Si solar cells. This paper presents an Ag-assisted chemical etching approach for single-crystal Si that generates wafer scale micro- and nano-porous textures with controlled surface morphologies and reflectance properties. The approach begins with an Ag thin film annealing process to form Ag micro- and nanoparticles on the Si substrate. This is followed by MaCE, where the Ag particles serve as a catalyst to produce a micro- and nano-porous texture on the Si surface. The morphology of the fabricated Si micro- and nanopores is controlled in accordance with the size and shape of the Ag particles, which are tuned by annealing the Ag films at different temperatures from 300 to 800 °C. The reflectance of the Si surface is in turn determined by the morphology of the etched texture. The fabricated Si antireflective textures have compound hierarchical structures, and an average reflectance of ∼4.7% is obtained when the Ag film is annealed at 600 °C.

Single-crystal Si solar cells with pulsed-DC sputtered SiNx:H anti-reflection film and phosphoric-acid-diffused n+ emitter

A low-environmental-load single-crystal Si solar-cell fabrication method was demonstrated, in which SiNx:H anti-reflection film was formed using a pulsed-DC reactive sputtering method with Ar and a forming gas (FG: 3.8% H2 in N2), and an n+ emitter was created using thermal diffusion of diluted phosphoric acid. In the SiNx:H film, it was shown that both exposure of the Si surface to FG plasma and FG annealing of the SiNx:H film dramatically decreased the surface recombination velocity, S, of the Si substrate, because of an improved Si/SiNx:H interface. The interface state density was found to be 2.1 × 1011 cm−2·eV−1 and the minimum S was 72 cm·s−1; these values are comparable to those obtained using the plasma-enhanced chemical vapor deposition method. The characteristics of the fabricated solar cells were: a short-circuit current of 38.1 A·cm−2, open-circuit voltage of 594.6 V, fill factor of 73.8, and an energy conversion efficiency of 16.7%.

Improvement of the Efficiency of Si Solar Cells Using Nano-Microscale Combination Patterns

Solar cells have a high reported energy conversion efficiency level according to various techniques. The energy conversion efficiency, however, is limited by the reflection of the light at the packaging glass surface. For this reason, some research groups are focused on nano/micro scale patterns. Nano/micro scale patterns can increase the energy conversion efficiency by means of light absorption. In this paper, we used three types of master stamps 300 nm pitch of a moth-eye pattern, a micro lens, and a hole pattern with a 200 nm diameter. These patterns were fabricated using UV-nanoimprint lithography on a cover glass which served as a protective layer of a Si solar cell. In additional, the transmittance and conversion efficiency of single-crystal Si solar cell were measured. Consequently, the conversion efficiency of a Si solar cell was found to increase from 16.69% to 18.16%.

ZnO Coated Nanoparticle Phosphors

ABSTRACTConventional phosphor materials are doped ternary or quaternary compounds; hence it would be difficult to prepare nanoparticles of those materials by build up methods. Ba2ZnS3:Mn (BZS), SrGa2S4:Eu, and BaAl2S4:Eu nanoparticles were prepared by a break down method, namely the ball-milling method. Transmission electron microscopy (TEM) and TEM- energy-dispersive X-ray spectroscopy (EDX) measurements showed several-nanometer-size stoichiometric and dispersed nanoparticles were achieved. ZnO-coating was performed and the uniform coating layers were formed on the phosphor nanoparticles. The ZnO-coated nanoparticles exhibited an improved stability in Photoluminescence. Red color phosphor material, namely BZS, was ball-milled and sprayed on the glass substrate. Mn doped BZS absorbs ultra violet light and emits red light peaking at around 640nm. When the single crystal Si solar cell was placed under the transparent nanoparticle layer, short wavelength light was absorbed and converted to long wavelength light.

Light trapping by a dielectric nanoparticle back reflector in film silicon solar cells

Drop-coated high-refractive-index nanoparticles used as a back reflector for thin-film solar cells are non-absorbing Mie-scatterers that enhance light trapping. We present optical measurements and theory for this approach. A 40% enhancement of the photocurrent and efficiency of a 2.5 μm thick single-crystal Si solar cell on display glass is achieved by adding a back reflector of 270 nm rutile TiO2 nanoparticles.

Plasmon Effect in Si Solar Cells Coated with a Thin Polymer Film Containing Silver or Gold Nanoparticles

To apply surface plasmon effects to Si solar cells, thin polymer films containing nanoparticles of silver and gold were fabricated using the spin-coating method. Advantages of this method are that it is simple, and that there is no possibility to produce additional crystal defects as surface recombination centers. Thin polymer films showed an absorption peak, anti-reflection effect and the haze ratio increase. In particular, thin polymer films containing gold nanoparticles were promising for improving Si solar cells, because the film had the longest peak wavelength and the lowest reflectance (3.84% at 800 nm), overall haze ratio increase caused by localized surface plasmon. Enhancement ratio in photocurrent conversion efficiency was 12% for single-crystal Si solar cells after being spin-coated with a thin polymer film containing gold nanoparticles. Enhancement ratio of the external quantum efficiency was 22% at the peak wavelength, caused by anti-reflection due to scattering by metal nanoparticles.

Direct Energy Conversion From Gamma Ray to Electricity Using Silicon Semiconductor Cells

AbstractSpent fuels and high level radioactive wastes which emit high doze of gamma rays could be a promising and long-lasting power source, if the gamma ray energy was effectively converted other forms of energy. In the present study, we have tried to convert gamma ray to electricity directly, with using silicon semiconductor cells made of p-type Si single crystal wafers with various specific resistivities ranging from 0.01 to 1000 Ohm∙cm. On both surfaces of the cell (20×20×0.5mm3), Al and Sb were deposited in vacuum to make electrodes at room temperature. The voltage-current measurement of the cells showed a rectification effect, and Al side was found to work a cathode. This suggests a Schottky junction was formed at the interface between the deposited Al and Si wafer. The cell irradiated by gamma ray in Co-60 irradiation facility in Kyushu Univ. with an absorbed dose of about 200Gy/h, and output voltage and current generated by the irradiation with external resistances varying from 200 to 100,000 Ohm were measured. The maximum electric power obtained for each cell ranged from 0.002 to 200 micro-W/m2, and clearly increased with increasing the specific resistivity of Si wafers. For comparison, a single crystal Si solar cell (2400mm2×0.5m, 0.5V×450mA in AM1.5 condition) was also exposed to the gamma ray, and its maximum electric power was 2 micro-W/m2. The output power of the present cell with high resistivity was two orders of magnitude higher than that of the Si solar cell.Energy deposition in the Si cell during gamma irradiation was evaluated with the Monte Carlo Simulation for N Particles (MCNP) code. For Si with 0.5 mm thickness, the deposited energy was calculated to be 17000 micro-W/m2 for 200Gy/h. Comparing the output energy by the gamma irradiation, the energy conversion efficiency of the present Si cells reached about 1%. Unfortunately, the present cells were unstable even in ambient atmosphere, the conversion ratio of which decreased to less than one tenth in six months. Further development of the cells with higher conversion ratio and improvement of its stability will be discussed.

Effect of glass frit chemistry on the physical and electrical properties of thick-film Ag contacts for silicon solar cells

The aim of this study is to understand the effect of the glass frit chemistry used in thick-film Ag pastes on the electrical performance of the silicon solar cell. The study focuses on the physical behavior of the glass frit during heat treatment as well as the resulting Ag−Si contact interface structure. We observe that the glass frit transition temperature (Tg) and softening characteristics play a critical role in the contact interface structure. The glass transition temperature also significantly influences the contact ohmicity of the thick-film metal grid. A high glass frit transition temperature generally results in thinner glass regions between the Ag bulk of the grid and the Si emitter. It was found that a glass frit (with high Tg) that crystallizes fast during the firing cycle after etching the silicon nitride and Si emitter results in smaller Ag crystallite precipitation at the contact interface. This results in smaller junction leakage current density (Jo2) and higher open-circuit voltage (Voc). Using high Tg pastes (with the appropriate Ag powder size), greater than 0.78 fill factors and >17.4% efficiency were achieved on 4 cm2 untextured single crystal Si solar cells with 100 Ω/sq emitters.

The behaviour of a typical single-crystal Si solar cell under high intensity of electric field

Abstract The effect of high intensity of electric fields on the operation of a single-crystal Si solar cell was investigated in this work. A single-crystal Si solar cell was irradiated by spontaneous and stimulated light sources. Firstly, a triac-lamp having a tungsten filament and green, yellow, red and blue LEDs from the spontaneous light sources were used to irradiate the solar cell exposed to a high-intensity electric field EDC. Later, as a stimulated light source He–Ne laser with λ = 633.8 nm and P = 1 mW was utilized, and the behaviour of the solar cell exposed to the electric field EDC ranging from 100×103 to 500×103 V/m was studied. The results showed that the Voc value of the solar cell irradiated by the two light sources mentioned above decreased due to the electric field.

Investigation of inhomogeneous structures of near-surface-layers in ion-implanted silicon

The ion implantation as a subject of investigations attracts increasing interest because of its technological applications. For example, the ion implantation and the adequate thermal treatment are the basic processes for fabrication of a new so-called delta-BSF solar cell. In this silicon solar cell, the continuous sub-structure of modified material (planar amorphous-like layer of nanometric thickness with very thin transition zones) is inserted into the single-crystal emitter. From earlier high resolution electron microscopy studies, it is evident that these two Si phases coexist in the form of well-defined layers separated by sharp heterointerfaces [Z.T. Kuznicki, J. Thibault, F. Chautain-Mathys, S. De Unamuno, Towards ion beam processed single-crystal Si solar cells with a very high efficiency, E-MRS Spring Meeting, Strasbourg, France, First Polish–Ukrainian Symposium, New Photovoltaic Materials for Solar Cells, October 21–22, Kraków, Poland, 1996.]. The aim of this paper is the further structural characterisation of silicon single crystal with buried `amorphous' layer. The non-destructive X-ray diffraction methods as well as the transmission electron microscopy were used to investigate the quality of the a-Si/c-Si heterointerfaces, structural homogeneity of the layers and distribution of the stress field. The measurements were carried out on an initial, as-implanted and annealed material. The 〈100〉-oriented Si single crystals were implanted with 180 keV energy P ions at room temperature.

Properties and Time Dependences of Silicon Oxynitride Films Deposited by Low-Temperature Photochemical Vapor Deposition

Silicon oxynitride films ( SiNx Oy ) were deposited using mercury-sensitized photochemical vapor deposition. The photochemical vapor deposition (photo-CVD) SiNx Oy film was used as an antireflective coating (ARC) for a single-crystal Si solar cell. It was found that the refractive index of SiNx Oy film deposited at low temperatures showed maked time dependence.

Plasma-Chemical Vapor-Deposited Silicon Oxide/Silicon Oxynitride Double-Layer Antireflective Coating for Solar Cells

Si-oxide/Si-oxynitride (SiOX/SiNXOY) double-layer films were prepared by controlling the operation parameters of plasma chemical vapor deposition in N2-diluted silane mixed with H2-diluted silane or with O2 under various mixing ratios. The compositions of the layers of the films were measured with electron spectroscopy for chemical analysis (ESCA) along the depth from the film surface by Ar-ion etching. The results have revealed that O-atoms diffuse into and N-atoms diffuse out of the SiNXOY layer during SiOX layer deposition. By making use of the relation between the refractive index and atomic ratio Si/O or O/N for SiNXOY films, the gradual changes of the refractive index in the SiOX/SiNXOY interfacial (or transition) region has been determined. As a result, the SiOX/SiNXOY double-layer antireflective coating (ARC) has increased the short circuit current density of single-crystal Si solar cells by about 56% in comparison to bare cells.

Improvement of Solar Cell Performance Using Plasma-Deposited Silicon Nitride Films with Variable Refractive Indices

Silicon nitride films containing various amounts of Si or O atoms were prepared by controlling the operation parameters of the plasma-chemical vapor deposition in N2-diluted silane mixed with H2-diluted silane or with O2 under various mixing ratios. By this method, the refractive indices of silicon nitride films could be varied over a wide range. The refractive index of films containing oxygen atoms gradually changed through oxygenation; however, oxygen-free plasma-deposited silicon nitride (P-SiN) films containing various amounts of Si atoms were very stable. The spectral response of the reflectance was measured for the latter Si-rich P-SiN films in order to determine the appropriate conditions as antireflective coatings for P/N single crystal Si solar cells. As a result, Si-rich P-SiN antireflective films improved the conversion efficiency of Si solar cells by 40 to 50 or by 50 to 70%, depending on whether a single-layer or double-layer coating, respectively, was used.

Proton radiation effects on Cr-MIS single-crystal Si solar cells

Cr-MIS solar cells on single-crystal Si, with a 2-cm2 area and approximately 10% efficiency, have been subjected to 1.0- and 1.6-MeV proton radiation at total dosages of up to 3.3×1013 p/cm2. Photovoltaic studies reveal characteristic short-circuit current and open-circuit voltage degradation similar to proton-irradiated junction-type solar cells. (See H. Y. Tada and J. R. Carter, Solar Cell Radiation Handbook, JPL Publication 77-56, 1977.) Spectral response measurements reveal output decay primarily due to minority-carrier diffusion-length decreases of up to 96%.