1,721,006 research outputs found
Surface photovoltage as a tool to monitor the effect of hydrogen treatment on a-Si:H/c-Si heterojunction
No full textThe amorphous/crystalline silicon technology has demonstrated its potentiality leading to high efficiency solar cells. We propose the use of surface photovoltage technique as a contact-less tool for the evaluation of the energetic distribution of the state density at amorphous/crystalline silicon interface. We investigate the effect hydrogen plasma treatments performed on thin amorphous silicon buffer layer deposited over crystalline silicon surface and we compare its effect with that of thermal annealing on the interface. The surface photovoltage technique results to be very sensitive to the different experimental treatments, and therefore it can be considered a precious tool to monitor and improve the interface electronic quality. © 2013 SPIE
Electroplated contacts and porous silicon for silicon based solar cells applications
No full textIn this paper, a two-layer metallization for silicon based solar cells is presented. The metallization consists of thin nickel barrier and thick copper conductive layers, both obtained by electrodeposition technique suitable for phosphorus-doped 70-90 Ω/sq solar cell emitter formed on p-type silicon substrate. To ensure the adhesion between metal contact and emitter a very thin layer of mesoporous silicon is introduced on the emitter surface before metal deposition. This approach allows metal anchoring inside pores and improves silicon-nickel interface uniformity. Optimization of metal contact parameters is achieved varying the anodization and electrodeposition conditions. Characterization of contacts between metal and emitter is carried out by scanning electron microscopy, specific contact resistance and current-voltage measurements. Mechanical strength of nickel-copper contacts is evaluated by the peel test. Adhesion strength of more than 4.5 N/mm and contact resistance of 350 μΩ cm2 on 80 Ω/sq emitter are achieved. © 2015 Elsevier B.V. All rights reserved
Aluminum-silicon interdiffusion in screen printed metal contacts for silicon based solar cells applications
No full textIn this work we propose a detailed investigation of the Al - Si interdiffusion that occurs during the firing process of the Al-Si back contact of silicon based solar cells. The investigation is based on high resolution scanning electron microscopy (SEM) and compositional microanalysis with energy dispersive X-Ray microanalysis (EDX). We have found a dependence of Si precipitation in the Al matrix depending on the microstructure of the Al screen printable paste. We suggest a gettering effect promoted by the larger Al particles lying within the Al paste being able to affect the Al paste resistivity, the Al distribution within the BSF region of the solar cell, thus affecting the solar cell performances and finally the Al paste thermal expansion coefficient. Finally we demonstrate that the presence of the glass frit reduces the surface tension and, homogenizes the diffusion process. Reduction of surface tension decreases the internal pressure and increases the Si interdiffusion in Al. © 2013 The Authors
New selective processing technique for solar cells
No full textA new selective processing technique based on a confined dynamic liquid drop\meniscus is presented. This approach is based on localized wet treatment of silicon wafers using confined and dynamic liquid drop that while in contact with the wafer forms a dynamic liquid meniscus. Such new technique allows to touch in specific defined positions the silicon wafer (front and/or back) in order to perform any kind of wet processing without the need of protective photo-resist. The new selective processing technique allows the metallizations (front and back) of mono and multi crystalline silicon solar cells. The front grid contacts are obtained by locally etching the silicon nitride, forming in a thin layer of meso-porous silicon and totally filling the meso-porous layer by pulse reverse plating a Nickel film. Copper and Tin are then electroplated using the same selective processing. This technology provides an effective solution to avoid silver pastes for front contact grid, as it guarantees low specific contact resistivity (550 μΩcm2 on a 75 Ω/□ n-type doped emitter) and good adhesion to the silicon substrate (i.e. greater than 550 g/mm). The Al back side of the solar cell are also treated by the new selective process. Tin is directly deposited on Aluminum back contact showing adhesion higher than silver on silicon (i.e. > 1N/mm). © 2013 The Authors
Porous silicon solar cells
No full textWe developed a new process for the fabrication of crystalline solar cell, based on an ultrathin silicon membrane, taking advantage of porous silicon technology. The suggested architecture allows the costs reduction of silicon based solar cell reusing the same wafer to produce a great number of membranes. The architectures combines the efficiency of crystalline silicon solar cell, with the great absorption of porous silicon, and with a more efficient way to use the material. The new process faces the main challenge to achieve an effective and not expensive passivation of the porous silicon surface, in order to achieve an efficient photovoltaic device. At the same time the process suggests a smart way to selective doping of the macroporous silicon layers despite the through-going pores. © 2015 IEEE
A new approach: Low cost masking material and efficient copper metallization for higher efficiency silicon solar cells
No full textA new approach based on the development of a new low-cost masking material and a new technique for performing fast wet processes (i.e. chemical etching and electroplating processes) are presented, back side silver removal is proposed allowing in combination with a multi-bus bar module assembly technique to boost standard silicon solar cells towards higher efficiencies at low cost. The new masking material based on a low-cost wax is able to withstand wet hot chemical treatment up to 100 °C. The developed wax composition that costs 10 times less than photoresist can be taken into consideration as an industrial masking process for solar cell for the front copper metallization process. However, the industrial applicability of the copper plating processes foresees several issues concerning the cell throughput for the plating technique at industrial level, which is directly connected to the plating speed. In this work, it is shown how using the new concept of coalescent dynamic liquid drop/meniscus is possible to plate 35 μm thick copper fingers on wax masked solar cell with a deposition speed as high as 1 μm/s. Combining the proposed technique with the back side selective plating, a silver-free silicon solar cell fabrication process is developed allowing to reach efficiencies higher than 18 % for monocrystalline silicon solar cell. © 2015 IEEE
Open circuit voltage reduction due to recombination at the heterojunction solar cell edge
No full textToday to achieve high efficiency solar cells, the crystalline silicon (c-Si) heterojunction (HJ) represents one of the best available options. The key factor of its success is the high open circuit voltage (Voc) achievable, because of the excellent surface passivation due to the intrinsic amorphous silicon (a-Si:H) layers. During cells manufacturing, the a-Si:H film deposition is simultaneously performed on both c-Si wafer sides, and consequently also on the edges of the wafer. However, the wafer edges could result non-passivated in many cases such as the so-called shingling manufacturing route. Moreover, at laboratory level it is quite common to manufacture small area cells from larger wafers. When a silicon edge is left uncovered by cutting, a recombining region is created due to the silicon non-passivated surface. This, in principle, leads to a reduction in the Voc of the cell. Nevertheless, this is not experienced for large area cells cut in half but it is commonly observed that cutting silicon HJ edges results in a lowering in Voc. In this work we have analyzed the correlation between the Voc, the cell area and the recombining surface introduced by cutting the cell into a smaller one. We have monitored the Voc as a function of the cell area during time, and we also have investigated the possibility of a re-passivation of the cell edges by depositing a thick a-Si:H layer after masking the sun exposed cell surface, exploring different deposition conditions to avoid re-annealing of the existing a-Si:H layers
Hydrogen plasma and thermal annealing treatments on a-Si:H thin film for c-Si surface passivation
No full textHigh efficiency solar cells can be fruitfully built using the amorphous/crystalline silicon technology, taking advantage of the high Voc that occurs as a consequence of excellent c-Si surface passivation provided by a-Si:H films. Improvements of the interface quality can be obtained using post deposition treatments such as hydrogen plasma and thermal annealing. We propose the use of surface photovoltage technique, as a contact-less tool to evaluate the energetic distribution of the state density at amorphous/crystalline silicon interface, and FTIR spectroscopy of the same samples to appreciate the evolution of Si-H and Si- H2 bonds. This approach leads to interesting applications for monitoring and improving the interface electronic quality, which is extremely susceptible to the different treatments adopted. We found that thermal annealing produces a metastable state which goes back to the initial state after just 48 hours, while the effect of hydrogen plasma post-treatment results more stable. Moreover H2 plasma reduces the defect density of one order of magnitude with respect to thermal annealing and keeps it constant also after one month. The hydrogen plasma is able to reduce the defect density but at the same time increases the surface charge within the a-Si:H film due to the H+ ions accumulated during the plasma exposure, leading to a more stable configuration
Laser Treatment to form An Effective Base Contact in a - Si:H/c-Si Heterojunction Solar Cells
No full textIn this paper we investigate the p-type a-Si:H/ia-Si:H/p-type c-Si structure, commonly used as base contact in amorphous/crystalline silicon heterojunction solar cell when fabricated on p-type c-Si wafer. Even though the most effective amorphous silicon/crystalline silicon heterostructure is based on n-type c-Si due to higher bulk lifetime, the p-type c-Si still remains the most common and cheaper substrate for silicon based solar cell. In particular we study the effect of localized 532 nm pulsed laser treatment at different laser conditions in order to reduce the cell series resistance due to the base contact. In this approach the p-type a-Si:H layer is used as a source of boron dopant. Depending on the thickness of the p-type a-Si:H film, when the laser beam is focused on p-type a-Si:H layer the boron can be transferred into the c-Si base to form an overdoped region and then an effective local Back Surface Field, able to enhance the hole collection at the metal of the base electrode in the p-type c-Si based heterojunction solar cell. The application of a thin Aluminum layer on top of the amorphous silicon to be treated by laser is also concerned. Series resistance of a transverse structure composed by the laser treated p-type a-Si:H/c-Si/opposite surface contacted by InGa is considered to optimize the laser procedure. Values as low as 0.5 Ωcm2 are obtained when the aluminum layer is adopted. © 2015 The Authors
Temperature effects on sputtered ITO
No full textIndium Tin Oxide (ITO) is widely used in solar cell devices for its excellent electrical and optical characteristics, such as high transparency in the Ultraviolet-Visible range and good conductivity (around 104W-1cm-1). In this work we have compared thin (70-150 nm) ITO layers deposited by Direct Current or Radio Frequency sputtering. We have used different substrate temperatures during film growthand have afterwards thermally annealed the samples at different temperatures up to 300 °C to investigate the effects on the electrical and optical properties of the material. We have found out that the different growth/annealing conditions induce changes in the optical properties of the samples as well as in the conductivity and carrier concentration. © 2018 IEEE
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