SiO2 Antireflection Research Articles

Novel-type nanostructured SiO2 antireflection coatings and their application in Cu(In,Ga)Se2 solar cells

Broadband antireflection coatings (ARCs) are a considerable way to sufficiently harvest more solar light into the solar cells due to dramatically reducing the reflection losses at the surface of substrate. Novel structures consisting of continuous SiO2 film and monodispersed SiO2 nanospeheres (NSs) array are proposed to fabricate ARCs according to mimicking the moth-eye-like nanostructure with a periodic sub-wavelength protuberance. Three distinct architectures of coatings based on SiO2 film and SiO2 NSs were successfully obtained by sol–gel dip-coating and electrostatic self-assembly technique, and the structural, morphological and optical properties of the coatings were investigated. Antireflection functionality of the coatings is achieved over the solar spectrum, and the solar transmittance of the substrate in visible region is increased by 7.02% on average with maximum of 8.21% by introducing coating of SiO2 NSs/SiO2 film. The power conversion efficiency of Cu(In,Ga)Se2 solar cells is clearly increased from 11.66% to 12.59% by using with as-prepared ARCs. The novel-type nanostructured ARCs are promising materials in both optical and photovoltaic applications.

Crystalline Silicon Solar Cells with Enhanced Light Trapping via Rear Side Diffraction Grating

Effective light trapping concepts are increasingly relevant for thinner crystalline silicon solar cells. Diffractive rear side structures can be designed to enhance optical light path lengths in the weakly absorbed infrared wavelength range. However, because of the rather difficult passivation of these nano-scale structures and possible plasma induced damages, the optical gain has so far not been shown on final device level for wafer-based crystalline silicon solar cells in combination with a high open circuit voltage.In this work, we fabricated and characterized silicon solar cells with an optically active layer at the rear side which is electrically decoupled from the silicon bulk by a thin, planar passivation layer. A binary diffraction grating was realized on the rear side via Nanoimprint Lithography (NIL) and plasma etching. For the rear side metallization a laser based foil process and photolithographically opened point contacts with evaporated aluminum were used as two alternative process routes. The best cell shows an EQE increase of up to 29 % absolute at 1100 nm compared to planar reference cells. This corresponds to a total Jsc gain of 1.2 mA/cm2 and a best cell efficiency of 19.4 % (Voc: 683.1 mV, Jsc: 35.4 mA/cm2, FF: 81.0 %) with planar front side and SiO2 antireflection coating.Optical simulations, which fit well to the experimental data, show that cell efficiencies of 20.8 % and 21.3 % can be reached with a planar front by using an optimized single layer (SiNxOy) or double layer (MgF, SiNx) ARC, respectively. By calculating Jsc for different cell thicknesses it is shown that a 100 μm thick solar cell incorporating the fabricated diffractive grating is expected to exhibit a higher Jsc than a planar cell with 250 μm thickness.

Y2O3: Eu3+, Tb3+ spherical particles based anti-reflection and wavelength conversion bi-functional films: Synthesis and application to solar cells

In this study, Eu3+ and Tb3+ co-doped Y2O3 particles were prepared via the simple, cost-effective urea homogeneous precipitation method without additives. The chosen particles were added in the SiO2 sols to get anti-reflection (AR) and wavelength conversion bi-functional films. Careful investigations were carried out to find the optimum preparation conditions and proper morphology. SEM images showed that the particle sizes reduced as metal ion/urea ratio decreased. Additionally, the extracted particles turned from sphere to lamellar type when the deionized water, which was used as solvent, reduced to a certain extent. The mechanisms of the morphology formation and diversification were proposed as well. The as prepared materials can convert UV region photos to visible photons between 460nm and 640nm, which just matched the spectral response of most solar cells. The spherical sample showed better luminescence performance than the one with lamellar morphology. In addition, the optical transmittance spectra indicated that the films adding spherical particles had better anti-reflective performance, and the best adding amount was 0.08g. Finally, As a proof-of-concept application, the as prepared bi-functional films were used to test the standard monocrystalline silicon solar cell assembled with anti-reflection and wavelength conversion bi-functional films photoelectric conversion properties. As a result, the as prepared bi-functional films could effectively improve the photoelectric conversion efficiency by0.23% compared to pure SiO2 AR coating film and 0.55% compared to glass.

Efficiency Enhancement of Cu(In,Ga)Se2 Solar Cells by Applying SiO2–PEG/PVP Antireflection Coatings

An effective approach was presented to enhance photoelectric conversion efficiency of Cu(In,Ga)Se2 (CIGS) solar cells by using modified SiO2 antireflection coatings (ARCs) to harvest more incident sunlight. Polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) used as additives were introduced into silica sols to prepare SiO2–PEG and SiO2–PVP coatings in the sol–gel dip-coating process, respectively. The different effects of PEG and PVP additives on SiO2 coatings were analyzed and the antireflection performance of SiO2–PEG and SiO2–PVP coatings was investigated. The transmittance over 97% ranging from 450 nm to 700 nm with a maximum transmittance over 99.40% at about 550 nm was achieved for both SiO2–PEG2000A and SiO2–PVP0.5 coatings. The relative efficiencies of CIGS solar cells coated with SiO2–PEG2000A and SiO2–PVP0.5 ARCs were increased by 7.27% and 8.33%, respectively. The modified SiO2 ARCs possessed the advantages of the low manufacturing cost, good adhesion, superior antireflective performance and the feasible method for large area fabrication.

Anti-reflection porous SiO2 thin film deposited using reactive high-power impulse magnetron sputtering at high working pressure for use in a-Si:H solar cells

Porous SiO2 thin films with low reflectance and high transmittance were obtained using reactive high power impulse magnetron sputtering (HIPIMS) at a high working pressure of 6.67Pa (50mTorr). The average transmittance (450–600nm) of the SiO2 thin films was 94.45%. In comparison, SiO2 thin films deposited at a low working pressure of 0.27Pa (2mTorr) showed an average transmittance of 91.26%. The improvement in the transmittance was attributed to the lower refractive index resulting from the porous structure of the SiO2 thin films. To examine the effect of the anti-reflection SiO2 coating, an a-Si:H solar cell was produced on fluorine-doped tin oxide (FTO) glass. The initial energy conversion efficiency for cells using the anti-reflection, SiO2-coated FTO glass was 11.75%, higher than the 10.75% for the sample using the bare FTO glass. The increase in the short-circuit current density (Jsc) due to the decreased light reflectance was the largest contributor to the increase in the a-Si:H solar cell efficiency.

Combined SiO2 antireflective coatings with MOCVD-ZnO:B to improve light absorption in thin-film solar cells

Boron-doped zinc oxide (ZnO:B or BZO) thin films prepared by metal organic chemical vapor deposition (MOCVD) are widely used as the front contact in thin-film solar cells. However, because reflection at the air/glass interface reduces the absorption of incident light, the short circuit current densities, as well as the efficiencies of the cells are deteriorated. To solve this problem, we proposed the combination of silicon dioxide (SiO2) antireflective (AR) coatings prepared by a sol–gel dip-coating method, with MOCVD-BZO films as the new substrate of the cell. The novel structure of the substrate obtained is: SiO2 AR coatings/glass/BZO. An improvement in the optical properties of the new substrate was achieved by destructive interference of the AR coatings at the coatings/air interface. Appling this novel substrate in amorphous silicon solar cells resulted in significant improvement of both the external quantum efficiency and the performance of the cell.

Investigation on Metal-Induced Crystallization of Amorphous Silicon Using Xenon Flash-Lamp

Flash-lamp annealing (FLA) is an alternative technique for crystallization of amorphous silicon which can be scaled to large substrates. A process using FLA may have significantly reduced process complexity and time; however published results that demonstrate potential for use in flat panel displays have been limited [1]. This work investigates FLA in combination with metal-induced crystallization (MIC). The FLA system used in this work is a NovaCentrix PulseForge 3300, which anneals the material using a series of short but intense bursts of broad spectrum light from xenon flash lamps. High peak power over microseconds time scale can provide control over the depth of heating to avoid damage when processing on substrates such as glass or plastic. Input factors to the FLA system included lamp intensity, pulse width, number of pulses and repetition rate. Since samples are not in thermal equilibrium during FLA, power/time/flash-count combinations that deliver the same energy produce very different results. Additional factors included use of an anti-reflective SiO2 layer, and substrate heating (steady-state). Performing FLA on samples with trace amounts of nickel has demonstrated effective crystallization with single-pulse exposures delivering energy of ~ 5 J/cm2. Experiments which investigate the influence of both MIC and FLA process parameters on the material properties and electrical characteristics of TFTs will be presented. [1] S. Saxena, D. C. Kim, J. H. Park, and J. Jang, "Polycrystalline silicon thin-film transistor using Xe flash-lamp annealing," IEEE Electron Device Letters, vol. 31, pp. 1242-1244, 2010

Mg-doped SiO2 porous coating with high anti-reflection in the visible spectrum

Mg-doped anti-reflection single-layer SiO2 coatings were fabricated on glass substrates by dip-coating method. The transmittance and refractive index of the coatings in the visible spectrum were significantly affected by the content of Mg2+ dopants and withdrawal speeds. A maximum transmittance of the Mg-doped anti-reflection coating was obtained when the content of Mg2+ dopants was 0.04mol% and the withdrawal speed was 350mm/min. Compared with bare glass substrate (89.7%), the maximum transmittance of the coating was greatly improved to 98.5% at 521nm. An even porous structure with small pores (about 30nm) was obtained and this structure can enhance transmittance of the coating in the visible spectrum.

New Cermet Coatings for Mid-temperature Applications for Solar Concentrated Combine Heat and Power System

New cermet (ceramic-metal) composite coatings have been developed for solar absorbers in a solar concentrating system for combined heat and power operating in a mid-temperature range between 250 to 350°C. The coatings were applied on stainless steel substrates. Two types of cermet with expected good duration properties were chosen: Nb-TiO2 and W-SiO2. The basic layer-structure concept consisted of four sub-layers, counted from the substrate: molybdenum infrared reflector, high metal concentration cermet of either Nb-TiO2 or W-SiO2, low metal concentration cermet of either Nb-TiO2 or W-SiO2 and SiO2 antireflection layer. The results from optimised coating fabrication gave solar absorptance and thermal emittance of 0.93 and 0.09 respectively for the Nb-TiO2 cermet and 0.91 and 0.08 for the W-SiO2 cermet based absorbers. Annealing at 350°C did not change the absorptance but decreased the thermal emittance with 0.01 units. Adhesion to substrate and between sub-layers was good and even improved after annealing. In a next step up-scaling to deposition on tubes has been made for the Nb-TiO2 cermet type coating and such absorbers are now operating in the solar concentrating combined heat and power demonstration plant in Malta.

Effect of Drawing Speed on Properties of the Anti-Reflective SiO<sub>2</sub> Film Based on Glass

The anti-reflective SiO2 film on glass was prepared by sol-gel process and dip-coating method.The effect of drawing speed on properties of the SiO2 film was studied. The transmittance was tested by light spectrum transmittance testing system,the thickness and refractive index of SiO2 film was tested by spectroscopic ellipsometer. With increasing of the drawing speed from 100mm/min to 300 mm/min, the average of transmittance increment at first increased and then decreased, which reached the maximum 4.24% at the speed 150mm/min. The relations among transmittance, thickness (d) and refractive index (n) of the SiO2 film was dicussed.

Preparation of single-layer antireflective SiO2 coating with broadband transmittance using PEG-modified sol–gel method

Adding polyethylene glycol (PEG) with different molecular weights, a usual acid-catalyzed sol–gel was modified to prepare single-layer antireflective SiO2 coatings with high and broadband transmittance and relatively better hardness. The test results of atomic force microscope and field emission scanning electron microscope show that the addition of PEG significantly affects the porosity and surface morphology of the coating layer. Due to the addition of PEG, the surface of the coatings presents groove-like and their porosity is increased, both of which contribute to the increase in transmittance. In the case of same PEG mass, PEG4000 modified coating has higher porosity and higher transmittance than PEG1000 modified one. In the present paper, the reflectance of samples for both sides was tested by ultraviolet–visible–near-infrared spectrophotometer (LAMBDA 950). The best coating’s reflectance can be decreased below 5 % from 460 to 1,740 nm. The transmittance peak value of the substrate is 90.6 % and its average value is 90.0 %, while the peak value of the best coating can reach up to 99.4 % and its average value is 95.5 % which increased by 5.5 % from wavelength of 325 to 1,000 nm. Hardness measurements show that the coatings have relatively better hardness.

Optimization of Porous SiO<sub>2</sub> Antireflective (AR) Coatings Used in Encapsulating Solar Modules

Base catalyzed sol-gel derived porous SiO2 coatings are prospectively used as antireflective (AR) layer for encapsulating solar modules. In this paper, the properties of SiO2 AR layers coated on solar glass by different dip-coating and annealing conditions are investigated and optimized. It is shown that the transmittance of the AR coating is affected by these preparation conditions which closely related to the thickness and surface morphology. As results, the SiO2 coating had a better performance both in transmittance and adhesion when the dip-coating speed and the annealing temperature are 0.036mm/s and 300°C respectively. Further more, TMCS hydrophobic treatment was adopted to make the AR coating meet the demands of practical application.

Study on antireflection SiO2 coatings fabricated by layer-by-layer deposition

Multifunctional (poly(diallyldimethyl ammonium chloride)/ sodium poly(4-styrene sulfonate))n((PDDA/PSS)n) thin films were fabricated by layer-by-layer assembled on the glass substrate. The monolayer silica nanoparticles were prepared on the (PDDA/PSS)n films. The SiO2-polyelectrolyte coatings exhibit antireflection properties with low refractive index (as low as 1.22). Interestingly, wavelengths of maximum transmittance could be well tailored by simply changing the particle size of SiO2. A maximum transmittance of 97.03% in the visible spectral range is achieved for the particle size of 100 nm SiO2 films. The coatings also show excellent mechanical stability and good adhesion to substrates. The easy availability of the raw materials and simplicity of the fabrication method for such films might make them be potentially useful for various applications.

Characterization of anti-reflective and self-cleaning SiO2–TiO2 composite film

Sol–gel dip-coating technique can be used to fabricate SiO2–TiO2 composite film with self-cleaning and anti-reflectance properties from low-cost SiO2 colloid solution and Ti(OC4H9)4. The physical and structural properties have been investigated by UV–visible spectrophotometer, contact angle meter, XRD, FT-IR, FESEM. UV–vis spectra and methyl orange photodegradation experiments showed that the SiO2–TiO2 composite film had high light transmittance and photocatalytic activity.

Optimization of the Dielectric Layer Thickness for Surface-Plasmon-Induced Light Absorption for Silicon Solar Cells

In this study, we investigate the effect of dielectric layer thickness on light reflection due to random self-assembled Ag nanoparticles with diameters of less than 160 nm deposited on the Si substrate, indicating that a dielectric layer with an appropriate thickness is useful for reducing the amount of reflected light. In the short wavelength range, reflectivity is determined by the metallic plasmon and the SiO2 antireflection layer, and the effect of the surface plasmon dominates over the antireflection effect. In the long wavelength range, reflectivity decreases with increasing dielectric layer thickness and is determined by the oxide antireflection layer, while the effect of the surface plasmon is negligibly small. Moreover, the surface plasmon is affected by the SiO2 layer and Si substrate when the dielectric layer is thin; however, it is only determined by the SiO2 layer when the oxide layer is sufficiently thick. These observations have substantial applications for the optimization of surface-plasmon-enhanced silicon solar cells.

Optimization of the Dielectric Layer Thickness for Surface-Plasmon-Induced Light Absorption for Silicon Solar Cells

In this study, we investigate the effect of dielectric layer thickness on light reflection due to random self-assembled Ag nanoparticles with diameters of less than 160 nm deposited on the Si substrate, indicating that a dielectric layer with an appropriate thickness is useful for reducing the amount of reflected light. In the short wavelength range, reflectivity is determined by the metallic plasmon and the SiO2 antireflection layer, and the effect of the surface plasmon dominates over the antireflection effect. In the long wavelength range, reflectivity decreases with increasing dielectric layer thickness and is determined by the oxide antireflection layer, while the effect of the surface plasmon is negligibly small. Moreover, the surface plasmon is affected by the SiO2 layer and Si substrate when the dielectric layer is thin; however, it is only determined by the SiO2 layer when the oxide layer is sufficiently thick. These observations have substantial applications for the optimization of surface-plasmon-enhanced silicon solar cells.

Preparation of Antireflection SiO2 Structures Based on Nanoimprinting Using Anodic Porous Alumina Molds

SiO2 pillar arrays with high aspect ratios were fabricated by nanoimprinting using ordered anodic porous alumina as a mold. The size and shape of SiO2 pillars could be controlled by changing the geometrical structures of the anodic porous alumina mold. The used of the obtained SiO2 fine patterns composed of ordered arrays of tapered pillars could effectively suppress the reflectance of incident light at the surface of the sample.

Study of multi-fractal spectrum of sol-gel hydrophobic anti-reflective SiO2 coating after laser-conditioning

Hydrophobic AR SiO2 coating was deposited on the K9 substrate with sol-gel dipping technique，and laser-conditioning was done in “R on 1" mode with Nd:YAG laser (1064nm，7.5ns). Laser-induced damage thresholds (LIDT) were measured by “1 on 1" mode，and fore-and-aft changes of the surface morphology and fractal structure of the coating caused by laser conditioning were investigated with atomic force microscope (AFM) and multi-fractal spectrum (MFS), respectively. The results showed that after laser-conditioning the LIDT of the coating increased obviously，the mean-square roughness decreaseds lightly and the surface of the coating became more smooth，and that width of MFS shrinked and the uniformity of distribution of fractal framework was improved. It means that the micro-structure of the surface of the coating become, so regular that the coating could resist more powerful laser irradiation. Further more，MFS is an effective method to research mechanism of high power laser irradiation on optical coating because we can acquire more information about the change of the surface structure of the coating.

Design realization and characterization of a position sensitive detector for fast optical measurement

The fabrication and testing results of a 65-pin ceramic packaged 4×4 arrayed position sensitive detector are presented. The detector, consisting of 16 tetra-lateral sensitive areas, is a p-n-n+ configuration made on 3-in. 111 n-type high resistance crystal silicon substrates. A 100-nm antireflection SiO2 thin film is formed on the surface, along with a multilayer cover glass with transmissivity >98% from 400 to 950 nm. Primary tests of the device show that it has a low dark current, high spectral sensitivity, very fast response speed, and very good linearity. The dark current of an element unit is less than 20 nA, which is the allowable maximum dark current. The peak spectral sensitivity of the sensor is over 505 mA/W at 800-nm wavelength. Its response time is 8 ns at 45-V reverse bias and the nonlinearity of the total sensitive area is less than 1%.

05/01662 Solar glass with industrial porous SiO2 antireflection coating: Measurements of photovoltaic module properties improvement and modelling of yearly energy yield gain

05/01662 Solar glass with industrial porous SiO2 antireflection coating: Measurements of photovoltaic module properties improvement and modelling of yearly energy yield gain