Antireflection Coatings For Solar Cells Research Articles

On the stability of optical properties of antireflection coatings for solar cells based on a silicon-silicon-oxide mixture

It is investigated how the storage duration influences the optical properties of antireflection coatings based on silicon-silicon-oxide mixture intended for silicon solar cells. It is shown that the spectral reflection coefficient changes by 2.7% for 22 years; i.e., the antireflection effect is retained. We draw the conclusion that coatings based on silicon-silicon-oxide mixture can greatly increase the lifetime of solar cells and a solar battery.

The application of double-layer silicon nitride films on the solar cell anti-reflection coatings

In this paper, reflectance features, external quantum efficiency, and energy conversion efficiency of mono-crystalline silicon solar cells with double-layer silicon nitride (SiNx) anti-reflection coatings were investigated. The simulated results by the PC1D software showed that the combination in which the bottom SiNx layer had a thickness of 35 nm and refractive index of 2.3, the upper layer had a thickness of 40 nm and refractive index of 1.9 achieved a minimum reflectance. Double-layer SiNx anti-reflection coatings were fabricated by adjusting the ratio of SiH4:NH3 in the PECVD growth. The measurement showed that the double-layer coatings had less reflectance than the single-layer coatings in short wavelength, while they did not show obvious changes in the range of 380 nm to 400 nm for the intensive absorption. Although the combination parameters were not optimum, the energy conversion efficiency of the double-layer SiNx anti-reflection coatings solar cell was improved from 17.88% to 18.03% comparing with the single-layer coatings.

Electro-deoxidation of thin silica layer in molten salt—Globular structures with effective light absorbance

This paper describes the electrochemical deoxidation of thin silica layer on silicon in molten salts. The oxide, 2μm in thickness, is formed on p-type silicon by thermal oxidation and electro-deoxidized in molten calcium chloride at 850°C. Distinctive surface architectures are obtained composed of spheres, nano-fibres and pores. The electro-deoxidized surfaces are formed, which absorb light up to 92% in the visible region of spectrum. This black silicon is attractive in many fields of application where specifically high silicon surface to volume ratio is of importance, in particular, in production of antireflection coatings in solar cells.

Optimization of porous silicon multilayer as antireflection coatings for solar cells

We present results of numerical simulation of optimized porous silicon (PS) multilayers used as antireflection coatings. For the simulations we introduce a figure of merit, which has into account the transmittance of PS multilayers, the solar cell internal spectral response and the solar spectrum. Using a realistic range of porosities in the simulations (from 40% to 90%) we found an optimal three layers configuration, which transfers to the cell 95.7% of the whole usable power. This value represents the 99.8% of the maximum attainable using the complete porosity range (from 0% to 100%). We fabricate the optimal PS three layers, achieving power transference to the substrate of 95.2%. In addition, taking advantage of the PS fabrication characteristics, we transferred a PS multilayer with specific optical response onto a crystalline silicon solar cell. This allows obtaining a tunable spectral response of the solar cell demonstrating the feasibility of transfer the porous antireflection coating onto any optical device.

Antireflection coatings for solar cells based on an alloy of a mixture of MgO and SiO2

Alloys of a mixture of MgO and SiO2 oxides are obtained using radiant heating. X-ray phase analysis shows that the mixture alloys are multiphase crystalline structures and solid solutions; they contain a glass phase and traces of the original oxides. For the mole: mole concentration, forsterite is identified in the composition of the composite material. It is found that films of an alloy of MgO and SiO2 deposited on the surface of glass and silicon wafers exhibit high mechanical strength and adhesion; they are transparent in the range of sensitivity of solar cells and can be used as antireflection coatings.

Structural and optical properties of Er 2O 3 films

Stoichiometric and amorphous Er 2O 3 films were deposited on Si(001) substrates by radio frequency magnetron technique. Spectroscopic ellipsometry measurement showed that the refractive index of the Er 2O 3 film in wavelength region of 400–1000 nm was between 1.6–1.7. The reflectivity of the Er 2O 3 films decreased greatly with respect to that from the uncoated Si substrates. The absorption coefficient of the Er 2O 3 film indicated that it had an energy gap larger than 4.5 eV. The obtained characteristics indicated that Er 2O 3 films could be promising candidates for anti-reflection coatings in solar cells.

Amorphous Er2O3 films for antireflection coatings

This paper reports that stoichiometric, amorphous, and uniform Er2O3 films are deposited on Si(001) substrates by a radio frequency magnetron sputtering technique. Ellipsometry measurements show that the refractive index of the Er2O3 films is very close to that of a single layer antireflection coating for a solar cell with an air surrounding medium during its working wavelength. For the 90-nm-thick film, the reflectance has a minimum lower than 3% at the wavelength of 600 nm and the weighted average reflectances (400–1000 nm) is 11.6%. The obtained characteristics indicate that Er2O3 films could be a promising candidate for antireflection coatings in solar cells.

Exploiting Silicon Porosity Gradients for Superior Antireflective Films

ABSTRACTAn electrochemical etching technique has been developed that provides continuous control over the porosity of a porous silicon (PSi) layer as a function of etching depth. Thin films with engineered porosity gradients, and thus a controllable refractive index gradient, have been used to demonstrate broadband antireflection (AR) properties on silicon wafers and solar cell substrates. This low broadband reflectivity is a direct result of the formation of a refractive index gradient at the substrate surface, where the transition between air and silicon occurs continuously throughout the thickness of a PSi film. These graded index films are formed by applying a continuously changing current function to the electrochemical cell during the PSi etch. The application of these films as solar cell AR coatings is of particular interest, where their broadband nature is a critical advantage. For this application, graded index PSi films must not only offer superior AR properties, but must also prove minimally disruptive to the electrical properties of the underlying solar cell. This requirement limits the total thickness of these films to approximately 120 nm, creating several challenges for this process. However, the simplicity and highly reproducible nature of this technique, in combination with its short duration (less than 10 seconds), make it a strong alternative to current vacuum deposited AR coating technology.

Deposition of SiO 2 and TiO 2 thin films by plasma enhanced chemical vapor deposition for antireflection coating

Silicon dioxide and titanium dioxide films were deposited at low temperature by electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (PECVD) using respectively O 2 and tetraethoxysilane (TEOS) or titanium isopropoxide (TIPT) as precursors. To control the thickness and the refractive index during deposition, the plasma reactor was equipped with an in situ spectroscopic ellipsometer. Deposition kinetics and layer properties were investigated by spectroscopic ellipsometry, X-ray photoelectron spectroscopy (XPS) and chemical etch rate. A double film antireflection coating was fabricated and reflectance was measured using a UV-visible near-infrared spectrometer. Results reported demonstrate that deposition of SiO 2 and TiO 2 films at low temperature by PECVD is a promising method to produce antireflection coatings for solar cells.

Laser-Induced Breakdown Spectrometry of Titanium Dioxide Antireflection Coatings in Photovoltaic Cells

Silicon photovoltaic cells have design and material requirements different from those of most other silicon electronic devices. Not only are nearly ideal silicon surfaces required, but also the bulk properties must be of uniform high quality for high-energy conversion efficiency. In this paper, emission spectra of laser-generated plasmas from titanium dioxide antireflection coatings in solar cells are reported. A pulsed nitrogen laser at 337.1 nm was used with a pulse width of 10 ns and a laser fluence of 8.6 J/cm(2) onto the sample. The plasmas were detected using a charge-coupled device. Depth profilings from several samples with different thicknesses of titanium dioxide have been studied. A method for measuring thin TiO(2) films based on the observation of such profiles was developed. The effect of the laser fluence on the sensitivity of the present method has been examined. Depth resolutions are fluence-dependent but are on the order of 40 nm. The dependence between titanium dioxide plasma intensity and material reflectivity at the laser wavelength is discussed. Another valuable aspect of the technique is the ability to perform measurements in a contactless manner at room temperature and atmospheric pressure on wafer-sized samples.

Modeling the growth of PECVD silicon nitride films for solar cell applications using neural networks

Silicon nitride films grown by plasma-enhanced chemical vapor deposition (PECVD) are useful for a variety of applications, including anti-reflection coatings in solar cells, passivation layers, dielectric layers in metal/insulator structures, and diffusion masks, PECVD nitride films are known to contain hydrogen, and defect passivation by hydrogenation enhances efficiency in polycrystalline silicon solar cells. PECVD systems are controlled by many operating variables, including RF power, pressure, gas flow rate, reactant composition, and substrate temperature. The wide variety of processing conditions, as well as the complex nature of particle dynamics within a plasma, makes tailoring Si/sub 3/N/sub 4/ film properties very challenging, since it is difficult to determine the exact relationship between desired film properties and controllable deposition conditions. In this study, silicon nitride PECVD modeling using neural networks has been investigated. The deposition of Si/sub 3/N/sub 4/ was characterized via a central composite experimental design, and data from this experiment was used to train optimized feed-forward neural networks using the back-propagation algorithm. From these neural process models, the effect of deposition conditions on film properties has been studied. It was found that the process parameters critical to increasing hydrogenation and therefore enhancing carrier lifetime in polysilicon solar cells are temperature, silane, and ammonia flow rate. The deposition experiments were carried out in a Plasma Therm 700 series PECVD system.

Screen-printed titanium dioxide anti-reflection coating for silicon solar cells

Application of a titanium organometallic ink for silicon solar cell anti-reflection coatings prepared by conventional thick-film printing methods is described. Several titanium organometallic compounds have been synthesized and tested afterwards. The optimum ink composition consists of di-isopropoxobis (pentane-2,4-dionato) titanium as the TiO 2 source, and terpineol, ethyl cellulose, butanol as the organic vehicle. The ink has been screen-printed onto polished silicon wafers and thermally treated at above 450°C to convert the printed layer to a glass-like oxide film. Reflection spectra and ellipsometric measurements have shown that the films are optically equivalent to those prepared by other more complex techniques. Silicon sol? cells with screen-printed metallization and anti-reflection coating have shown as much as 35? in efficiency over the uncoated devices.

Plasma-enhanced CVD silicon nitride antireflection coatings for solar cells

Multilayer plasma-enhanced chemical vapor deposition (PECVD) silicon nitride antireflection coatings were deposited on space quality silicon solar cells. Preliminary experiments indicated that multilayer coatings decreased the total reflectance of polished silicon from 35 per cent to less than 3 per cent over the spectral range 0.4–1.0 μm. The solar cell energy conversion efficiency was increased from an average of 8.84 per cent to an average of 12.63 per cent.

Optical studies of multilayer dielectric-metal-dielectric coatings as applied to solar cells

In this paper a study of antireflection coatings for solar cells which provide maximum transmittance in the range of the spectral response of the cell and maximum reflectance in the IR portion of the spectrum of normally incident radiation is reported. Dielectric-metal-dielectric filters with a relatively low number of dielectric layers are designed as coatings for silicon and GaAs solar cells.

Sputtered Ta2O5 antireflection coatings for silicon solar cells

Ta2O5 thin films were deposited onto monocrystalline silicon surfaces by magnetron reactive sputtering. When the Ta2O5 films are employed as antireflection coatings, the reflectance of the original silicon surface diminishes from about 30% to approximately 3%. At the same time, a very low absorption coefficient (less than 103 cm-1) for the Ta2O5 films below their fundamental absorption edge (hv < 4.2 eV) is obtained from reflectance and transmittance spectra of Ta2O5 deposited onto quartz substrates. Finally, the technique of reactive sputtering is considered from the point of view of preparing antireflection coatings for solar cells.

Spray pyrolysis in solar cells and gas sensors

The present article offers a review of the technique of spray pyrolysis deposition of thin films. General aspects of the method, such as its inherent simplicity and low energy consumption, are briefly considered. The basic process and apparatus utilized in spray pyrolysis are described in general and also for particular applications. Specific techniques used to deposit thin films of metal oxides, oxide semiconductors, sulfide and selenide semiconductors and related compounds, and the properties of the resulting deposited films are discussed. The most common applications of these sprayed films are presented, with special reference to recent results in gas detection and photovoltaic solar energy conversion, including thin film solar cells, solar cell antireflection coatings, and thin film gas sensors. A general review of the published work in these areas is also included, together with a number of pertinent references.

Antireflection coatings for solar cells

Antireflection coatings for solar cells

Antireflection coatings for solar cells

The design factors, materials, and methods used to provide antireflection coatings on solar cells are described. The dependence of coating properties on the cell requirements is discussed. The methods used are well understood, and a firm basis exists for evaluation of impoved methods or materials for reducing cell reflectance.