Water jet-assisted green recycling of si-solar cell module waste is demonstrated, allowing a green process for the recovery of end-of-life solar modules. This eco-friendly process ensures glass recovery without surface damage or residual traces, eliminating the need for multi-step procedures.
Thermophotovoltaics (TPV) is a versatile technology to generate high electrical power density utilizing multiple sources of heat, such as solar irradiation, radioisotope heaters, combustible materials, thermal storage systems, waste industrial heat etc., as input. TPV systems aim to surpass the efficiency beyond the Shockley-Queisser limit for photovoltaic conversion by tailoring the spectrum of the incident solar light to match the spectral response of a PV cell. Spectrally selective absorbers and emitters can greatly enhance the TPV conversion efficiency by maximizing the absorption of the incident sunlight and suppressing the emission of sub-bandgap and excessive energy photons. One approach of achieving spectral selectivity is through the use of micro and nanostructures to control light emission from surfaces. This presentation reviews optical modeling and characterization techniques of various types of novel nanostructures, including random textures, nanocones, nanoholes, and m ultilayer metal dielectric stack etc., for the design of high-performance selective surfaces needed for efficient TPV systems. In addition, the fabrication of a GaSb-based experimental TPV system comprising a multilayer metal-dielectric (Si3N4-W-Si3N4) coating-based selective emitter is also presented. The performance of the TPV system was evaluated using a high-power laser as a simulated input for concentrated solar power. The overall power conversion efficiency of 8.4% was measured at 1676 K.
A method of doping germanium using 1064 nm pulsed fiber laser was demonstrated. The secondary ion mass
spectrometry showed a p-n junction of 800 nm deep with a peak phosphorus concentration of 2×1019 cm-3. Germanium
photodiodes were fabricated on the laser-doped p-n junctions. Low bulk and surface leakage current values were
obtained which were comparable to diodes fabricated by rapid thermal diffusion. Laser doping allows low thermal
budget, minimization of surface desorption and selective doping without requiring photolithography. Laser doping was
shown to be an effective method for fabrication of electronic and optoelectronic devices.
The laser processing of thick aluminum foil (8 μm) has the potential of providing low resistance metal contacts and reducing the fabrication cost for silicon solar cells. A high-power nanosecond pulsed laser with wavelength of 1064 nm was used in combination with a soda-lime glass substrate to make electrical contacts between aluminum foil and silicon where the glass substrates allowed flattening of the foil for laser processing. The initial demonstration was performed by passing a laser beam through glass and irradiating an aluminum foil to contact p-type silicon through a passivation layer of SiOx. Cross-section morphologies of resultant line contacts were investigated. A specific contact resistivity as low as 1.8 mΩ-cm2 was achieved based on measurements by the Transmission Line Method (TLM). A non-vacuum laser assisted rear metallization process based on cost-effective aluminum foil is feasible for silicon solar cell fabrication.
Laser micromachining is one of many laser material processing technologies employed in scientific research and engineering applications. It involves the deposition of photon energy and the material interaction. The intense photothermal energy is transported into the target material causing melting and evaporation. The material is removed layer by layer by melting and flowing away or by direct vaporization / ablation. It is due to the focused small spot size that the laser micromachining can remove material in small quantity at a time, thus precise control of geometrical dimension is possible. In this work, a nanosecond pulsed Nd:Yttrium-Aluminum-Garnet (Nd:YAG) laser was employed to generate relatively long notch of different dimensions (25.4 mm-length × 0.1 mm-width × 0.051/0.102/0.152 mmdepth) on Ti-3Al-2.5V seamless tubes for fatigue life study. Cyclic hydraulic impulse pressure test was conducted to find out the fatigue limits of the titanium tube containing the laser micromachined notch. The results of fatigue lives, crack profile and pattern of crack propagation are presented and discussed in this paper. Scanning electron microscopy was employed to characterize the fatigue crack profile and the laser micronotch. The capability of generating sharper notch root and consistent pre-crack on the surface of materials makes nanosecond pulsed Nd:YAG laser a great choice in preparing for fatigue test samples for crack growth life study.
Studies on surface texturing by chemically enhanced laser ablation in a variety of materials, particularly silicon and
germanium are reported. The materials are exposed either to femtosecond or nanosecond laser irradiation in a variety
of vacuum or gaseous environments including air, He, sulfur hexafluoride (SF6) or hydrogen chloride (HCl). The
dynamics of pillar formation are elucidated and it is shown that the mechanisms are very different in these two pulse
length regimes. Surface texturing responds to the combined effects of laser assisted chemical etching and laser
ablation. Various processing steps either before or after laser irradiation allow us to modify the nature of the pillars
that are formed. In this way we can make ordered arrays that extend over ≥1 cm2 in just a few minutes of laser
exposure. Post-laser processing wet etching can produce Si pillars that are over 50 &mgr;m long with tips that are only 10
nm across as well as macroporous silicon with crystallographically defined pores. A process we call solidification
driven extrusion creates nanoscale spikes atop the pillars under certain circumstances - a process that is more
prevalent for Ge than Si. Pillar-covered surfaces of Si and Ge are black; that is, they exhibit very low reflectivity. For
Si this low reflectivity extends to wavelengths far below the band gap raising the possibility that we may be able to
make other transparent materials highly absorptive by laser texturing.
The present study deals with the works relating to integrated watershed management on sustainable basis for evolving tractable operational package so that nutrient, sediment and runoff losses from catchment could be minimized.
Study area lies between latitudes 22°5' and 22°12' and longitudes 77°17' and 77°23' covering an area of 6357.5 hectares. Physically it is divided into two different parts, hills and plains. The height of elevation of study area is in between 518 to 630 meters above m.s.l. The thematic maps were generated using satellite data.
The present tropical catchment possessing diverse forest ecosystem and agriculture land characterized by weathered black cotton soil derived from basalt with the slope ranging from nearly level to moderately steep to steep sloping and receiving average annual rainfall 1150 mm.
The annual return of carbon and nutrient (N, P, K, Ca, Na and Mg) in non degraded and degraded forest and nutrient concentrations in runoff flow and sediment output (sediment loss) during monsoon period from non-degraded forest, degraded forest and agriculture lands were worked out.
The sediment and nutrient losses from the catchment to the tropical water body are alarming particularly from agricultural land. The nutrient losses in both the forms (runoff water plus sediment movement) are in the order of agriculture > degraded forest > non-degraded forest. The loss of soil in the form of sediment loss follows the same pattern. The results were alarming when the value of sediment loss of forest was compared to the agriculture land of the catchment. The soil loss as sediment is 33.5 times greater in agriculture land compared to non-degraded forest and 10.2 times greater in agriculture land compared to degraded forest.
Results of semiconductor laser crystallization of a-Si:H on transparent conducting fluoride doped tin oxide coated glass are discussed. A-Si:H films were prepared by plasma enhanced chemical vapor deposition. Laser crystallized films of a-Si:H were characterized by X-ray diffraction and optical microscopy. Semiconductor laser crystallization process as compared to well-established excimer laser offers low cost large area technology for solar cell, display and other applications. Longer wavelength of diode lasers (805 nm) allows light to penetrate deeper in the films for crystallization of thicker films required for enhanced light absorption.
Laser micromachining of n-type silicon wafer was studied using femtosecond laser operating at 400 and 800 nm wavelengths. The fundamental wavelength was used to fabricate a diaphragm of 4 mm diameter using a computer controlled galvo head. The laser pulsewidth was 110 fs, repetition rate of 1 kHz, and maximum average power of 2 W. The experiments were done in air and in vacuum environment. The samples were examined with optical microscope and surface profilometer. Experiments were also done with doubling the laser beam frequency using LBO crystal to get 400 nm wavelength. Using a 10 nm resolution stage, high numerical aperture microscope objective, we were able to fabricate 235 nm wide lines with 600 nm depth.
We present the results of a study of the optical properties of channel waveguides fabricated in z-cut lithium tantalate single crystals through proton-exchange in pyrophosphoric acid. A mask with lines 4 micrometers wide was used to fabricated these waveguides. The extraordinary effective refractive indices and near-field mode profiles of a waveguide proton-exchanged at 260 degree(s)C for 12 min and annealed at 400 degree(s)C for up to 3 h, are measured for TM polarized laser light at wavelengths 442, 543, 632, and 780 nm. The effective indices of the waveguide were measured through prism coupling. We observed that the variation of the extraordinary effective index with annealing time displays the anomalous behavior reported previously in the literature and it is maximum for an annealing time of 9 min. Using a prism coupler to individually excite each mode, we measured the near-field mode profiles by magnifying and imaging the end of the waveguide onto an optical multichannel analyzer. The variation of the FWHM in the width and depth directions as a function of wavelength and annealing time are presented. For the longest annealing time, we compare our results with the theoretical predictions obtained through numerical modeling.
An in-built internal field of 5 KV/mm was measured in Z-cut LiTaO3 single crystals in the direction of the original polarization. This was reflected in the asymmetry (along the field axis) in the polarization hysteresis curve as a function of external electric field. Measurement of internal field as a function of crystal thickness revealed that the internal field is a volume effect. Using infrared absorption measurements, the spectrum of the hydroxl ions (OH-) present in these crystals was measured at room temperature. The shape of the spectrum changes with polarization reversal in these crystals indicating a strong correlation with the direction of internal field with respect to the polarization direction. It suggests that the origin of internal field lies in point defect complexes involving OH- ions.
We present the results of an experimental study of photorefractive damage caused by laser light at a wavelength of 488 nm in z-cut lithium tantalate bulk crystals and channel waveguides. The photorefractive damage was measured using both imaging technique and interferometry. Initially, we measured the photorefractive damage in virgin-poled crystal samples of various grades purchased from several sources. As expected, the amount of photorefractive damage is least in optical-grade crystals. In addition, we compared photorefractive damage in waveguides fabricated in virgin-poled and periodically poled optical-grade z-cut crystals. Our results confirm that the amount of photorefractive damage that occurs during irradiation is less in periodically poled waveguides. Furthermore, heating the waveguide devices to a temperature of 100 degree(s)C during irradiation removes most of the visible distortions of the waveguide mode profile that result from photorefractive damage for both the virgin-poled and periodically poled waveguides.
The coercive field for domain reversal in a 0.5 mm Z-cut LiTaO3 was measured to be 21 KV/mm. However, if the polarization of the crystal is reversed using an electric field of 21 KV/mm, the coercive field for a second reversal is found to be 11 KV/mm. This asymmetry is due to the presence of an in-built internal field of 5 KV/mm in the virgin crystal. If the electron beam writing is done on the new C-face of the polarization reversed region of the crystal, (1) no cracking was observed, (2) the writing required less charge for domain inversion because of the reduced coercive field, thereby facilitating shorter scan times. We have obtained uniform 3.6 micrometers period domain inversion grating using this technique.
We report a process for the formation of inverted ferroelectric domain regions in LiTaO3. This process involves ion exchange followed by domain inversion by a uniform electric field. The resultant periodic domain structure is applicable to first order quasi-phase-matched second-harmonic generation. In first order periodically poled crystals of Z-cut LiTaO3, initial results have shown bulk conversion efficiencies of up to 3%/(W-cm). A second- harmonic conversion of 3 mW of blue wavelength power was observed from waveguide devices made on these crystals.
Results of polarization separation characteristics of surface relief gratings are presented. Use of such gratings for multifunction signal detection of optical disk is discussed.
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