Antireflection coatings on plastics deposited by plasma polymerization process

Antireflection coatings (ARCs) are deposited on the surfaces of optical elements like spectacle lenses to increase light transmission and improve their performance. In the ophthalmic industry, plastic lenses are rapidly displacing glass lenses due to several advantageous features. However, the deposition of ARCs on plastic lenses is a challenging task, because the plastic surface needs treatment for adhesion improvement and surface hardening before depositing the ARC. This surface treatment is usually done in a multi-stage process—exposure to energetic radiations, followed by deposition of a carbonyl hard coating by spin or dip coating processes, UV curing, etc. However, this treatment can also be done by plasma processes. Moreover, the plasma polymerization process allows deposition of optical films at room temperature, essential for plastics. The energetic ions in plasma processes provide similar effects as in ion assisted physical deposition processes to produce hard coatings, without requiring sophisticated ion sources. The plasma polymerization process is more economical than ion-assisted physical vapour deposition processes as regards equipment and source materials and is more cost-effective, enabling the surface treatment and deposition of the ARC in the same deposition system in a single run by varying the system parameters at each step. Since published results of the plasma polymerization processes developed abroad are rather sketchy and the techniques are mostly veiled in commercial secrecy, innovative and indigenous plasma-based techniques have been developed in this work for depositing the complete ARCs on plastic substrates.     

Multifunctional bioinspired sol-gel coatings for architectural glasses

Although several multinational companies have recently released products incorporating bioinspired functional coatings, their practical integration in building envelopes is still an open issue. High production costs associated to the existing vacuum deposition technologies, as well as the difficulties in extending the number of functions achievable by a single coating, represent to date the main limitations to their diffusion on a large scale. This review summarizes the key topics in the field of functional coatings for architectural glasses, focusing in particular on the potential applications of sol-gel based antireflective and self-cleaning coatings, that have received a tremendous attention in the last years. It provides an overview of the recent research efforts aimed to improve their properties and to extend their range of applicability. The bioinspired principles, upon which such coatings are based, are also described and are related to the chemical and morphological properties of such surfaces.     

Antireflective porous layer formation on multicrystalline silicon by metal particle enhanced HF etching

Antireflection of silicon (Si) surface is one key technology for the manufacture of efficient solar cells. Metal particle enhanced HF etching is applied to produce uniform antireflecting porous layer on multicrystalline Si wafers that cannot be uniformly texturized by anisotropic etching with an alkaline solution. Fine platinum (Pt) particles are deposited on multicrystalline n-Si wafers by electroless displacement reaction in a hexachloroplatinic acid solution containing HF. Both macroporous and luminescent microporous layers are uniformly formed by immersing the Pt-particle-deposited multicrystalline Si wafers in a HF solution. The reflectance of the wafers is reduced from 30% to 6% by the formation of porous layer. The photocurrent density of photoelectrochemical solar cells using porous multicrystalline n-Si has a 25% higher value than non-porous Si cells.     

Antireflection of glazings for solar energy applications

Several antireflection treatments such as Teflon dipping, dipping in silica saturated fluosilic acid, have previously been tested. The films made with the fluosilicic acid showed an increased solar transmittance of up to 5%. Outdoor testing for more than 7 years indicated an excellent long-term stability. The problem with this process is the involved chemicals, which are too harmful to permit a large-scale production in Sweden. Therefore, a dip-coating process has been investigated, which uses silica sols. Two sols were investigated, one polydisperse and one monodisperse. The highest attained solar transmittance was achieved with the monodisperse sol. It is believed that the increase in the solar transmittance is connected to the size of the silica particles, the larger the smallest particles the higher the solar transmittance. A decrease by up to 5.2% in the solar reflectance has been noted. A problem is the mechanical properties and especially the adhesion tends to be low. It is, however, possible to improve these properties by baking the film at approximately 550°C during 30 min. The solar transmittance decreases when baking the film since it collapses partially, but the mechanical properties seemed to improve. During baking the temperature is close to that of commercial tempering. It should therefore be possible to bake and temper at the same time. The deposited film does not introduce any absorption. It is concluded that this process should be suitable for large-scale production, since the involved chemicals are harmless and the process is fairly rapid. Films were made at withdrawal rates of up to 1 cm/s.     

Texture optimization process of ZnO:Al thin films using NH4Cl aqueous solution for applications as antireflective coating in thin film solar cells

ZnO:Al thin films varying the thickness from 80 to 110 nm were deposited on polished float zone < 100 > Si wafers by radio frequency magnetron sputtering at 100 °C. To texturize these surfaces with the aim of being used as antireflective coating, a wet etching process based on NH₄Cl was applied. Taking into account that the layer thickness was small, the control of the etch parameters such as etchant concentration and etching time was evaluated as a function of the textured film properties. An appropriate control of the etching rate to adjust the final thickness to the 80 nm required for the application was realized. Using NH₄Cl concentrations of 10 wt.% and short times of up to 25 s, an increase of the film roughness up to a factor of 5.6 of the as-deposited films was achieved. These optimized textured films showed weighted reflectance values below 15% and considerable better electrical properties than the as-deposited 80 nm-thick ZnO:Al films.     

Process modeling and optimization of PECVD silicon nitride coated on silicon solar cell using neural networks

The process of plasma enhanced chemical vapor deposition silicon nitride films coated on silicon solar cells as antireflection layers is modeled and optimized using neural networks. This neural network model is built based on the robust design technique with process input–output experimental data. The input parameters selected are as substrate temperature, SiH₄ and NH₃ flow rates, and RF power; while the output parameters are deposition rate, refractive index, and short circuit current. This model can then be applied to predict the input–output relationships of the process. Optimal operating conditions of this process can be determined using this model.     

具有激光二极管结构的1.3μm侧面发光二极管（Ⅱ）：实验结果

文章给出了用部分参数不合格的激光二极管（ＬＤ）制作具有激光二极管结构的侧面发光二极管＊ＬＤＳ－ＥＬＥＤ）的实验结果。     

新型红外增透膜与保护膜

综述了近年来几种新型红外光学材料－类金刚石、金刚石、碳化锗及磷化硼薄膜的发展现状，详细论述了这些光学材料的性能特点、制备方法、应用前景、存在的关键问题以及未来的发展方向。     

Amorphous hafnium oxide thin films for antireflection optical coatings

Hafnium oxide (HfO₂) thin films were grown on silicon and quartz substrates by radio frequency reactive magnetron sputtering at temperature < 52 °C. X-ray diffraction of the films showed no structure, suggesting that the films grown on the substrates are amorphous. The optical properties of these films have been investigated using spectroscopic ellipsometry with wavelength range 200-1400 nm and ultraviolet-visible spectrophotometer techniques. Also, the effects of annealing temperatures on the structure and optical properties of the amorphous HfO₂ (a-HfO₂) have been investigated. The films appeared to be monoclinic structure upon high temperature (1000 °C) annealing as confirmed by X-ray diffraction. The results show that the annealing temperature has a strong effect on the optical properties of a-HfO₂ films. The optical bandgap energy of the as-deposited films is found to be about 5.8 eV and it increases to 5.99 eV after the annealing in Ar gas at 1000 °C. The further study shows that the measurement of the optical properties of the amorphous films reveals a high transmissivity (82%-99%) and very low reflectivity (< 8%) in the visible and near-infrared regions at any angle of incidence. Thus, the amorphous structure yields HfO₂ film of significantly higher transparency than the polycrystalline (68%-83%) and monoclinic (78%-89%) structures. This means that the a-HfO₂ films could be a good candidate for antireflection (AR) optical coatings.     

Fabrication of silicon nanowire arrays based solar cell with improved performance

We report fabrication of solar cell (n⁺-p-p⁺ structure) on black silicon substrates consisting of silicon nanowire (SiNW) arrays prepared by Ag induced wet chemical etching process in aqueous HF-AgNO₃ solution. SiNW arrays surface has low reflectivity (<5%) in the entire spectral range (400-1100 nm) of interest for solar cells. The solar cells were fabricated by conventional cell fabrication protocol. Performance of three types of cells, namely cell with SiNW over the entire front surface, cell with SiNW only in the active device area and control cell (on planar surface), has been compared. It was found that cell based on selectively grown shorter length SiNW arrays has the best cell performance.