Aluminum Paste Research Articles

Water Soluble Aluminum Paste Using Polyvinyl Alcohol for Silicon Solar Cells

Screen-printing aluminum is still dominantly used in the solar cell fabrication process. Ethyl cellulose is one of the main contents of screen-printing pastes that require dichloromethane for its cleaning process, a substance renowned for being extremely toxic and threatening to the human body. Developing environmental friendly aluminum pastes is essential in order to provide an alternative to the commercial pastes. In this work, new, nontoxic polyvinyl alcohol-based aluminum pastes are introduced. Polyvinyl alcohol was used as a soluble polymer that can be synthesized without saponification and that is also soluble in water. Three different pastes were developed using different recipes including many aluminum particle sizes varying from 3.0 to 45 μm, aluminum oxide with particle sizes between 35 and 50 μm, and acetic acid. Evaluation of the pastes was carried out by Scanning Electron Microscope (SEM) image analysis, sheet resistance measurements, and fabricating silicon solar cells using each paste. Solar cells with 15.6% efficiency were fabricated by nonvacuum processing on CZ-Si p-type wafers using developed aluminum pastes on the back side.

Electroless metallisation of ABS plastic: a comparative study

The present work incorporates comparative evaluation between three different routes for metallisation of copper on ABS parts. These routes are aluminium paste (Al paste) coated ABS parts, chromic acid for etching of ABS part and use of H2SO4/H2O2 for etching ABS parts. The main focus is to find out the best route for metallisation of ABS parts among the three routes employed. Scanning Electron Microscopy (SEM) with energy dispersive spectrometer images and electrical performance are used for comparative work. Finally, it was concluded that Al-pasted parts are best suited for metallisation of copper on them.

Performance improved by point‐contact electrodes and SiO 2 /SiN X layers at rear

The rear point-contact fabricated through the laser-opening technique for mass production was applied on the photovoltaic cells. Laser opening, different layers for passivation (SiO2) and protection (SiN X ) were employed to investigate their impact on the performances of solar cells. The SiN X layer protects the SiO2 layer from being burnt through by aluminium paste at the co-firing step. A conversion efficiency (η) of 16.91% with an open-circuit voltage of 628 mV was obtained for the optimal cell, a stack structure with SiO2 and SiN X layers, which also achieves a lower contact resistance of 6.66 mΩ·cm2 and a higher light-beam-induced current of 80.77 mA/cm2. The optimal cell also showed longer lifetime and 3–4% increased quantum efficiency in the visible wavelength range. Therefore, the developed process has simplicity and reliability, is fast and cost-effective and could be applied to industrial applications.

자동차 선도장용 베이스코트에서 알루미늄 입자 크기와 형태에 따른 물성 연구

The formulation of six basecoats was designed using aluminium pastes for the per-painted system in the automotive. The aluminium pastes contain pancake type metallic pigment, #501, #801, #601 and cornflake type metallic pigment, #750, #770, #790. The relative cure density of the basecoat increased in order of #501, #801, #601, #750, #770, #790. T-bending, impact resistance, and taping adhesion showed increment with increasing cure density. In the appear- ance(combined factor) test on cornflake type pigment, The basecoat including the smallest particle size pigment, #790 resulted in the best combined factor compared to other two systems(#750, #770).

Effects of silicate glasses in aluminum pastes on physical and electrical characteristics of screen-printed multi-crystalline silicon solar cells

Aluminum pastes (APs) with various silicate glasses (SGs) have been synthesized to enhance physical and electrical characteristics of screen-printed multi-crystalline silicon solar cells (SPMSSCs). The improved back surface field (BSF) and decreased tortoise-shell veins were demonstrated by suitably Si–Bi–B-doped Si–Bi–Ti-based oxide SGs in APs. The promoted mechanism could be attributed to the circulating track supplied from binary SGs softened in APs during co-firing. The achievement of a conversion efficiency improvement of more than 1.34% absolute from 16.01% to 17.35% in SPMSSCs with a binary Si–Bi–Ti of 1wt% and Si–Bi–B of 3wt% SGs in AP was explored.

Anisotropy of Compressive Strength in Porous Alumina Ceramics

Anisotropy of the compressive strength was investigated in porous alumina based ceramics produced by slip casting method. Aluminium paste was used as pore former similarly as in the aerated concrete technology. Materials were sintered at 1650°C and 1750°C. The apparent porosity of the investigated materials was in the range of 54±1% to 60±2%. The compressive strength of the samples in the directions parallel and perpendicular to the sample expansion direction was in the range from 3.8±0.3 to 13.0±1.1 MPa and from 6.4±1.3 to 27.0±1.1 MPa, respectively. The mechanical anisotropy was related with the flattening of the introduced pores. The level of mechanical anisotropy was affected by the initial composition of the slurry and sintering temperature.

Metallization on FDM Processed Parts Using Electroless Procedure

Metallization has been studied on flat ABS (acrylonitrile-butadiene-styrene) parts. These parts were fabricated on fused deposition modelling machine using layer by layer deposition principle using ABS as part material. Electroless copper deposition has been performed on these parts using three different surface preparation processes namely aluminium paste (Al paste) coated ABS parts, surface prepared using chromic acid for etching and ABS parts prepared using H2SO4/H2O2 for etching. Surface preparation is followed by Cu (copper) deposition by electroless procedure using four different acidic baths. The acidic baths used are 5 wt% CuSO4 (copper sulphate) with 15 wt% of individual HF (hydrofluoric acid), H2SO4 (sulphuric acid), H3PO4 (phosphoric acid) and CH3COOH (acetic acid) acids. Cu deposition is presented and compared based on their electrical performance, scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). The results shows that Al pasted samples demonstrated better electrical performance and more uniform Cu deposition.

Cracks in Solar Cell Metallization Leading to Module Power Loss under Mechanical Loads

We investigate the mechanisms leading to electrically insulated cell parts in a photovoltaic module under mechanical load. For this we measure the resistances across a crack in a laminated solar cell during bending that is typical in the field. The cracks in the solar cell are detected with electroluminescence imaging. The resistance over the aluminum paste increases continuously by negligible 30 mΩ whereas the front finger resistance increases by 15.4 kΩ stepwise. This difference is the result of the higher ductility of the aluminum paste in comparison to the front finger metallization. We associate the steps in the front finger resistance measurement to breakage of single fingers with an equivalent circuit model. Furthermore we found that a silicon crack widths lower 2μm has no influence on the resistances. Crack widths higher than 7μm leads to a complete front finger interruption. We determine that the specific resistance of such a crack causes nearly 100% of the power loss, which is caused by a completely electrically insulating crack in a photovoltaic module.

Application of ion Implantation Emitter in PERC Solar Cells

Ion-implantation offers numerous advantages (i.e., single-side precise control and reproducibility of the dopant, simultaneous SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> passivation during annealing, no phosphosilicate glass formation) for solar cell manufacturing. Canadian Solar Inc. has developed an average efficiency 19.23% blank emitter solar cell (156 mm Cz) process using a high-throughput Varian (Applied Materials) Solion ion-implant tool. In order to improve solar cell efficiency, focus is placed on the well-known advanced passivated emitter and rear cell solar cell architecture with optimized backside passivation. The approach is to combine the surface passivation provided by a thin atomic layer deposition aluminum oxide layer grown after the post implantation annealing process with a deposited capping silicon nitride layer. Laser ablation and proper aluminum paste is also used to locally remove the dielectric layers and to form local contact. Based on this development, implanted emitter and local Al-BSF with Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> back passivation are integrated in solar cells, reaching an average efficiency of 19.96% and champion 20.12%.

Study on the Performance of Aluminum Thick Film Contacts for Silicon Solar Cells&lt;sub&gt;&lt;/sub&gt;

Aluminum rear contacts of silicon solar cells are made commonly by screen-printing aluminum paste and sintering process. Aluminum thick film contacts have a direct effect on photoelectric properties of solar cells, like open circuit voltage (Voc), short circuit current (Isc), conversion efficiency (η), etc. The principle of Al-back surface field (BSF) has been studied in this paper. With thermal gravimetric analysis and differential scanning calorimetry (TGA-DSC) method, the chemical reactions between aluminum thick film and silicon substrate during heat treatment have been investigated. The microstructure of aluminum thick film contacts were analysed by SEM. The electrical properties of Al-BSF are improved by adding a proper amount of nano silicon to the aluminum paste.

Direct Metallization Local Al-Back Surface Field for High Efficiency Screen Printed Crystalline Silicon Solar Cells

In this paper, we present a detailed study on the local back contact (LBC) formation of rear-surface-passivated silicon solar cells, where both the LBC opening and metallization are realized by one-step alloying of a dot of fine pattern screen-printed aluminum paste with the silicon substrate. Based on energy dispersive spectrometer (EDS) and scanning electron microscopy (SEM) characterizations, we suggest that the aluminum distribution and the silicon concentration determine the local-back-surface-field (Al-p+) layer thickness, resistivity of the Al-p+ and hence the quality of the Al-p+ formation. The highest penetration of silicon concentration of 78.17% in aluminum resulted in the formation of a 5 microm-deep Al-p+ layer, and the minimum LBC resistivity of 0.92 x 10-6 omega cm2. The degradation of the rear-surface passivation due to high temperature of the LBC formation process can be fully recovered by forming gas annealing (FGA) at temperature and hydrogen content of 450 degrees C and 15%, respectively. The application of the optimized LBC of rear-surface-passivated by a dot of fine pattern screen(-) printed aluminum paste resulted in efficiency of up to 19.98% for the p-type czochralski (CZ) silicon wafers with 10.24 cm2 cell size at 649 mV open circuit voltage. By FGA for rear-surface passivation recovery, efficiencies up to 20.35% with a V(OC) of 662 mV, FF of 82%, and J(SC) of 37.5 mA/cm2 were demonstrated.

자동차용 선도장 베이스코트에서 알루미늄 입자 크기와 배향에 따른 내후성 연구

자동차용 선도장 베이스코트 도료에서 사용되는 알루미늄의 입자 크기와 배향에 따른 내후성을 연구하였다. UV를 촉진하여 조사할 수 있는 QUV<TEX>$^{(R)}$</TEX> (Q-LAB) 장비를 이용하여 UV 투과율의 차이에 의한 소재의 손상 정도를 관찰하였다. Conflake 형태의 입자 크기가 서로 다른 3종의 알루미늄 paste를 이용하여 자동차용 선도장 조건으로 베이스코트를 도장하고 투명 클리어를 도장하여 필름과 시편을 제조하였다. 작성된 필름을 UV 투과 장비로 측정한 결과 입자 크기가 작고 수평 배향인 EKART사의 #790을 사용 시 낮은 UV 투과율을 나타내었다. 실제 내후성 시편의 단면 조사에서도 #790, #770, #750 순으로 높은 광택 유지율을 나타내었다. Weatherability was examined according to aluminum particle size and its orientation used in PCM(Paint Coated Metal). Substrate delamination was checked by different UV transmission rate with QUV<TEX>$^{(R)}$</TEX> (Q-LAB) equipment that can make accelerated UV irradiation. Film was prepared using three different types of conflake aluminum pastes under a PCM coating process and clearcoat was sprayed. UV transmission test results showed low transmission rate when EKART #790 having the smallest particle size and horizontal orientation was used. From the gloss retention results, gloss retention was highest in EKART #790 and followed by #770, #750.

Understanding the Properties of Silicon Solar Cells Aluminium Contact Layers and Its Effect on Mechanical Stability

As the thickness of silicon solar wafer and solar cells becomes thinner, the cells are subjected to high stress due to the thermal coefficient mismatch induced by metallization process. Handling and bowing problems associated with thinner wafers become increasingly important, as these can lead to cells cracking and thus to high yield losses. The goal of this work to provide experimental understanding of Al rear side microstructure development and mechanical properties as well as correlate the obtained results with fracture behaviour of the cell. It is shown that the aluminium back contact has a complex microstructure, consisting of five main components: 1) the back surface field layer; 2) a eutectic layer; 3) spherical (3 - 5 μm) hypereutectic Al-Si particles surrounded by a thin aluminium oxide layer (200 nm); 4) a bis- muth-silicate glass matrix; and 5) pores (14 vol%). It was concluded that the eutectic layer thickness and waviness depends on Al particle size, amount of Al paste and textured surface roughness of silicon wafers. The Young’s modulus of the Al-Si particles is estimated by nano-indentation and the overall Young’s modulus is estimated on the basis of bowing measurements and found to be ~43 GPa. It was found, that there is a relation between aluminium paste composition, eutectic layer thickness, mechanical strength and bowing of solar cells. Three main parameters were found to affect the mechanical strength of mc-silicon solar cells with an aluminium contact layer, namely the eutectic layer thickness and uniformity, the Al layer thickness (which results from the Al particle size and its distribution), and the amount of porosity and the bismuth glass fraction.

Investigation of Aluminum-boron Doping Profiles Formed by Coalloying from Screen-printed Pastes

We present a detailed study on aluminum-boron doping profiles formed in silicon by alloying from screen-printed aluminum pastes containing boron additives. We show that an increase in the effective peak temperature Tpeak,eff (determined from phase diagram calculations) of the alloying process leads to higher concentrations of both Al and B atoms within the alloyed p+ region, resulting in (i) higher potential barriers for electrons, but also (ii) increased densities of recombination-active Al defects. While the improved potential barrier predominates for Tpeak,eff ≲ 770°C, the increased defect density prevails for Tpeak,eff ≲ 800°C, thus defining an optimal effective peak temperature. Furthermore, we show that, by increasing the amount of elemental B added to the paste, the acceptor concentration can be increased without affecting the defect density. Therefore, the optimal printing and firing conditions comprise high B amounts and low, adapted effective peak temperatures. For a B content of 0.9 wt% and Tpeak,eff = 765°C, we have achieved a saturation current density of 253 fA/cm2, corresponding to an implied open-circuit voltage of 665mV, which demonstrates the high potential of B additives within Al pastes to further improve the efficiency of Si solar cells with Al-alloyed p+ rear.

Alloying From Screen-Printed Aluminum Pastes Containing Boron Additives

We present a detailed study on alloying from screen-printed aluminum pastes containing boron additives (Al-B pastes) to further enhance the efficiency of p- and n-type silicon solar cells with an Al-alloyed back-surface field and rear emitter, respectively. Due to the high B solubility in Si, the additional incorporation of B atoms as acceptors into the Al-alloyed p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> region-referred to as Al-B codoping of Si-provides improved shielding of electrons from the recombination-active surface. Thus, alloying from Al-B pastes allows for significantly thinner p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> regions and leads to a considerable reduction of the p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> saturation current densities. By comparing surface-passivated p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> regions alloyed from Al-B pastes or conventional Al pastes with each other, we show that a highly recombination-active defect limits the minority carrier lifetime in these p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> regions. We demonstrate that the acceptor concentration profiles of the p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> regions can easily be modified by adding different amounts of aluminum diboride or boron trioxide as B sources to the Al pastes.

Influence of kaolin and firing temperature on the mullite formation in porous mullite-corundum materials

The refractory ceramics became very important in both the traditional and the advanced materials applications as it has outstanding thermal and mechanical properties. The refractoriness of ceramics can be achieved by getting the mullite-corundum. Refractory ceramics with high porosity serve as a heat insulator and constructional material. Three series of porous mullite-corundum ceramic samples were prepared from Al2O3 (Nabalox, Germany) and pure SiO2 in 2.57:1 ratio that was conformed to mullite compositions (3Al2O3·2SiO2). α-Al2O3 (d50 = 4 μm) and γ-Al2O3 (d50 = 80 μm) were in 1:3 ratio. Quantity of kaolin (MEKA, Germany) was 10, 20 and 30 wt.%. Porous materials were prepared by slip casting of suspension of raw materials, where the aluminium paste (0.18 wt.%) was used as a pore former. Water content in the suspensions was 38-40 wt.%. Pore formation occured in result of hydrogen formation in chemical reaction between aluminium paste and water. The samples were sintered at 1650, 1700 and 1750°C temperature for one hour. SiO2 and γ-Al2O3 on the contrary reduced mechanical properties, but decreased shrinkage. Using of α-, γ-Al2O3, SiO2 and kaolin in corresponding ratios the samples with open porosity of 30 to 54 vol% were acquired. The relative amounts of pores depended on the initial content of kaolin and on firing temperature.

Evaluation of Series Resistance Losses in Screen-Printed Solar Cells With Local Rear Contacts

We demonstrate industrially feasible large-area solar cells with passivated homogenous emitter and rear achieving energy conversion efficiencies of up to 19.4% on 125 mm × 125 mm p-type 2-3 Ω·cm boron-doped Czochralski silicon wafers. Front and rear metal contacts are fabricated by screen printing of silver and aluminum paste and firing in a conventional belt furnace. However, these cells suffer from moderate fill factors below 76% due to an increased series resistance. In this paper, we analyze the main cause of this increase. We vary the rear contact geometry over a wide range. By subtracting the respective contribution of the base from the measured series resistance, we extract a value of (55 ± 10) mΩ·cm2 for the effective specific contact resistivity of our screen-printed local aluminum rear contacts. We verify this value by local series resistance mappings from photoluminescence measurements resulting in a contact resistivity of (40 ± 10) mΩ·cm 2. Our analysis reveals that the highest potential for a further energy conversion efficiency improvement is to decrease the rear contact resistivity.

Investigation of Aluminum-Alloyed Local Contacts for Rear Surface-Passivated Silicon Solar Cells

We present a comprehensive study on the rear contact formation of rear surface-passivated silicon solar cells by full-area screen printing and alloying of aluminum pastes on the locally opened passivation layer. We show that the point contact distance has a significant influence on the local alloying process for the contact formation resulting in different structural and electrical contact properties when applying conventional Al pastes. Increasing the distance leads to 1) high contact depths resulting in an enlargement of the contact area and 2) severely reduced thicknesses of the Al-doped p+ regions in the contact points, leading to a strong increase in recombination within the contact points. This inadequate contact formation can be directly linked to the deficiently low percentage of silicon that dissolves into the Al-Si melt during alloying. We demonstrate that by intentionally adding Si to the Al paste, the contact point geometry can be significantly improved and particularly becomes independent of the contact distance. Further investigations on the internal reflectance and the specific resistivity of the rear contact suggest an upper limit for the Si content added to the Al paste. In summary, we present a simple way to significantly improve the rear contact formation of rear surface-passivated silicon solar cells.

Aluminum Alloying in Local Contact Areas on Dielectrically Passivated Rear Surfaces of Silicon Solar Cells

We present a detailed study on the rear contact formation of rear-surface-passivated silicon solar cells by full-area screen printing and alloying of aluminum pastes on the locally opened passivation layer. We demonstrate that applying conventional Al pastes exhibits two main problems: (1) high contact depths leading to an enlargement of the contact area and (2) low thicknesses of the Al-doped p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> Si regions in the contact points resulting in poor electron shielding. We show that this inadequate contact formation can be directly linked to the deficiently low percentage of silicon that dissolves into the Al-Si melt during alloying. Thus, by intentionally adding silicon to the Al paste, we could significantly improve the contact geometry by reducing the contact depth and enlarging the Al-p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> thickness in the contact points, enabling a simple industrially feasible way for the rear contact formation of silicon solar cells.

Microstructural and electrical properties of different-sized aluminum-alloyed contacts and their layer system on silicon surfaces

The firing of screen-printed aluminum pastes is well established for the formation of a back surface field (BSF) and back contacts since many years in silicon solar cell fabrication. In this paper we investigate the electrical and microstructural properties of Al-alloyed contacts and their layer system, consisting of (i) the Al-doped p +-layer (2–14 μm), the eutectic layer (1–15 μm) and the layer of paste residuals (20–100 μm). We show the influence of process parameters like the amount of printed paste, the alloying time and the peak temperature. Special emphasis is devoted to the properties of small alloyed screen-printed aluminum structures for the formation of local aluminum back contacts. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), electrochemical capacitance voltage (ECV) and conductivity measurements have been applied to characterize the samples. A simple model is qualitatively augmented to describe all effects occurring in a technical alloying process. For example, for increasing aluminum amounts, a saturation of the p +-layer thickness was found in the range of 10 mg/cm 2. For small screen-printed structures, the p +-layer is formed very homogenously and with a greater thickness compared to samples with a full-area Al metallization, which have been processed with similar alloying conditions. For the eutectic layer a high electrical conductivity of about 16×10 6 S/m, only 2–3 times below that of pure aluminum has been determined. This is advantageous for the lateral conductivity especially for high paste amounts and small structures, which feature a relatively thick eutectic layer.