14 research outputs found
Nanosphere concentrated photovoltaics with shape control
No full textDielectric colloidal nanospheres (NSs) are promising candidates for light management in photonic devices such as solar cells (SCs). NS arrays can direct the broad incident solar radiation into a set of tighter foci, at which light intensity becomes considerably concentrated, enabling higher photovoltaic conversion efficiency. Furthermore, the NS arrays acting as an effective medium on the SC surface can reduce reflectance and facilitate improved forward scattering. Therefore, uniform arrays of NSs located on top of the SC can behave as antireflection coatings or as microlenses, which can be regarded as a surface distributed light concentrator within the framework of concentrated photovoltaics. Fabrication of NS‐based light‐trapping structures is low‐cost and less complicated than common alternatives such as vacuum evaporated multilayer antireflection coatings. In this work, experimental demonstration and computational confirmation on the shape adjustment of such NS structures for improved light harvesting and efficiency enhancement in Si SCs are studied. The light conversion efficiency of Si solar cells is shown to improve by more than 27% with shape adjustment of NS arrays
ARKA KONTAK ARKA EKLEMLİ SİLİSYUM GÜNEŞ HÜCRELERİNİN TASARIM, ÜRETİM VE KARAKTERİZASYONU
No full textThe design and development of high-efficiency interdigitated back contact (IBC) solar cells have been studied within the scope of this thesis. Developing a totally industry-compatible, lithography-free, high-throughput process flow for IBC cell fabrication was the main motivation of the thesis. For this, a detailed simulation study was conducted using Quokka 2 software to optimize the rear side cell geometry and understand the effect of bulk and layer properties on the device performance. After determining three different cell geometries with varying pitch values of 750, 1250, and 1700 µm, a totally screen-printing-based process flow was designed and applied to fabricate IBC cells. For selective diffusion, thick SiNx layers with optimized layer compositions were used as the diffusion barriers during the high-temperature boron and phosphorus diffusion process. The patterning of the barrier layers was done using a screen-printable ink with enhanced chemical resistance in acidic solutions. Following the optimization of the diffusion barrier properties and corresponding patterning step, diffusion and corresponding passivation properties were optimized. BCl3 and POCl3 diffusion recipes were studied in detail not only for the rear emitter and back surface field (BSF) regions but also for the front non-contacted junctions. Industrial fire-through (FT) metals pastes were used for the metallization of rear junctions whose corresponding optimization was done with the help of detailed contact resistivity analysis. Combining all optimized process parameters for the cell fabrication resulted in best cell parameters as FF:71.2%, Voc:642 mV, Jsc:37 mA/cm2 for FFE-IBC cell structure which were FF:70.3%, Voc:637 mV, Jsc:39 mA/cm2 for FSF-IBC structure.
In addition to IBC studies, polySi passivating contact cells were also focused on in this thesis. In addition to their passivating properties, ex-situ doped polySi layers of varying thicknesses were studied also for their contacting properties. Excellent passivation properties were obtained for the case of n-polySi layers with the corresponding total recombination parameters (J0) of 1.6 and 7.4 fA/cm2 on textured and polished wafers, respectively. For the case of p-polySi layers, 16.3 and 70.2 fA/cm2 were obtained on the polished and textured wafers. Regarding the contacting properties, a novel methodology to extract the contact recombination parameter (J0,contact) was developed. The extracted J0,contact values were lying within the range of 300-400 fA/cm2 for relatively thicker n-polySi and p-polySi layers which increased to 1000 and 700 fA/cm2 for their thinner counterparts. Obtained J0,contact values were then correlated to high-resolution SEM images to better understand the contact formation and paste-polySi interaction.Bu tez kapsamında yüksek verimli iç içe geçmiş arkadan bağlantılı (IBC) tipi güneş hücrelerinin tasarım ve geliştirilmesi çalışılmıştır. Tezin ana motivasyonu tamamen endüstriye uyarlanabilir, litografi gerektirmeyen, yüksek üretim çıktılı bir IBC üretim yöntemi geliştirmektir. Bu amaçla, Quokka 2 yazılımı kullanılarak arka yüzey geometrisinin optimize edilip, silisyum alttaş ve üzerindeki tabakaların özelliklerinin aygıt performansı üzerindeki etkisi simüle edilmiştir. Simülasyon çalışmalarının ardından 750, 1250 ve 1700 µm hücre açıklığına üç farklı yapı seçilmiş ve önerilen tamamen serigrafi tabanlı IBC üretim yöntemi bu üç farklı hücre geometrisi için kullanılmıştır. Hücre aşamasında seçici difüzyon için kompozisyonu optimize edilmiş kalın SiNx tabakaları yüksek sıcaklık bor ve fosfor katkılama işlemleri sırasında bariyer olarak kullanılmıştır. Bariyer tabakalarının desenleme işlemi serigrafi ile serilen, asidik solüsyonlarda kimyasal dayanımı yüksek olan özel bir mürekkep kullanarak yapılmıştır. Difüzyon bariyeri özellikleri ve ilgili desenleme işlemlerinin optimizasyonun ardından, katkılama ve yüzey pasivasyonu çalışmaları devam etmiştir. Hem arka yüzey emiter ve arka yüzey alanı (BSF) hem de ön yüzey kontak atılmamış eklem bölgeleri için BCl3 ve POCl3 difüzyon reçeteleri detaylı bir şekilde çalışılıp, optimize edilmiştir. Metalizasyon için endüstriyel metal pastalar kullanılmış, kontak direnci çalışmaları yardımıyla gerekli optimizasyonlar tamamlanmıştır. Optimize edilmiş tüm proses parametreleri kullanılarak üretimi tamamlanan FFE-IBC hücrelerde en iyi hücre parametreleri FF:%71.2, Voc:642 mV, Jsc:37 mA/cm2 seviyelerine ulaşırken, FSF-IBC hücreler için bu değerler FF:%70.3, Voc:637 mV, Jsc:39 mA/cm2 seviyesine çıkmıştır.
IBC çalışmalarına ek olarak, çoklu kristal silisyum (polySi) ile pasive edilmiş hücreler de bu tez kapsamında incelenmiştir. Pasivasyon özelliklerinin yanı sıra haricen katkılanmış polySi katmanlarının kontak özellikleri de farklı tabaka kalınlıkları için incelenmiştir. N-tipi polySi tabaka için parlak yüzeylerde 1,6 ve piramitli yüzeyde 7,4 fA/cm2 gibi oldukça düşük seviyelerde toplam rekombinasyon parametrelerine (J0) ulaşılmıştır. P-tipi polySi tabakalar için toplam J0 değerleri parlak yüzey için 16,3 ve piramitli yüzey için 70,2 fA/cm2 seviyelerine kadar düşürülmüştür. Kontak özellikleri düşünüldüğünde ise, kontak rekombinasyon kayıp parametresi (J0,contact) hesaplaması için özgün bir yöntem geliştirilmiştir. Bu yöntem kullanılarak elde edilen J0,contact değerleri kalın olan n-tipi ve p-tipi polySi tabakaları için 300-400 fA/cm2 seviyelerinde kalırken, daha ince olan n-tipi ve p-tipi polySi tabakaları için bu değer sırasıyla 1000 ve 700 fA/cm2 kadar yükselmiştir. Elden edilen J0,contact değerleri sonrasında yüksek çözünürlüklü taramalı elektron mikroskobu (HR-SEM) görüntüleriyle ilişkilendirilip kontak oluşum mekanizması ve metal pasta-polySi tabakası etkileşimi daha iyi anlaşılmıştır.Ph.D. - Doctoral Progra
Enhanced metal assisted etching method for high aspect ratio microstructures: Applications in silicon micropillar array solar cells
No full textA solar cell device, fabricated on high density array cylindrical pillars, enables photogenerated carrier collection in the radial direction, thus shortening the path length of the carriers reaching the junction. It also provides advantages over conventional planar junction solar cells, such as reduced surface reflectance and enhanced light trapping. In this study, highly ordered Si micropillars were fabricated by photolithography and metal assisted etching (MAE) methods. It is shown that the use of ethanol as a solvent during the etching process and increasing HF concentration in the MAE solution both improve the quality of the surfaces of the pillars. Micropillars with smooth sidewalls and a high aspect ratio were obtained in this way. Solar cells with a radial junction were then fabricated on these micropillars. Standard doping, SiO2/SiNx passivation, and metallisation steps were carried out for the fabrication of solar cells with different micropillar lengths. A significant decrease in reflectance values was observed as the micropillar length increased, as expected. Solar cell short circuit current density (J(SC)) and efficiency (eta) of the solar cells tended to increase with micropillar length up to 11.5 mu m and then decrease due to increased surface recombination. The maximum efficiency achieved in this study is 17.26%
Concentrated Photovoltaics Using Shape-modified Nanospheres
No full textLight management is one of the main functions of dielectric colloidal nanospheres (NSs), which is beneficial in photonic devices like solar cells (SCs). NSs can direct the broad incident light into several concentrated tighter foci, which results in improved photovoltaic conversion efficiency. Also, the NS arrays can be employed as an effective medium on the SC surface to decrease reflectance and enable better forward scattering. As a result, not only can uniform arrays of NSs on the surface of the SC behave as antireflection coatings, but they also act as micro-lenses, which are considered surface distributed light concentrators that can be utilized in the field of concentrated photovoltaics. The fabrication of NS-based light-Trapping structures is cost-effective and simple compared to other options such as vacuum evaporated multilayer antireflection coatings. In this study, experimental results of shape modified NS structures resulting from annealing entail improved light harvesting and better efficiency in Si SCs. The light conversion efficiency of Si solar cells is demonstrated to enhance by more than 19% with shape adjustment of NS arrays
Hydrogen thermal activation of defects enabling firing stable Poly-Si based passivating contacts for TOPCon solar cells
No full textPassivating contacts based on poly-Si/SiOx also referred to as TOPCon (tunnel oxide passivated contacts) have substantially improved the performance of crystalline silicon (c-Si) solar cells. Hydrogenation in TOPCon has the utmost importance for achieving high quality surface passivation and enhanced solar cell performance. In this work, the hydrogenation mechanism and high-temperature fast firing behavior of phosphorus-doped TOPCon structures, on textured crystalline Si; coated with ALD–AlOx, PECVD–SiNx, and AlOx/SiNx stacks, are investigated. Using hot plate annealing series, our results show that thermal activation for hydrogenation is required for TOPCon/AlOx, while the hydrogenation is already activated for TOPCon/SiNx. For AlOx, activation energies (EA) are calculated in the 0.28 – 0.52 eV range, implying that hydrogenation is reaction limited rather than bulk diffusion of hydrogen atoms. The effect of TOPCon layers (SiOx and poly-Si thickness, ex-situ phosphorus diffusion, AlOx/SiNx) is explored. Among all, SiOx is the most critical factor affecting the firing stability. The firing stability is achieved for TOPCon/1.2 nm SiOx with iVOC of 720.6 mV and J0S=3.03 fA/cm2 while excellent passivation with iVOC of 735.1 mV and J0S=2.73 fA/cm2 are not maintained in TOPCon/1.6 nm SiOx after fast firing. The reason for this stability difference is explained by the fact that higher number of interfacial defects in 1.2 nm SiOx is beneficial for preventing blister formation during fast firing
Light Trapping by Micro and Nano-hole Texturing of Single-crystalline Silicon Solar Cells
No full textAbstractThe efficiency of a solar cell strongly depends on the interaction between the incoming light beam and the surface of the device. Any process enhances light-surface interaction increases absorption probability of the light; thus, improves generated current, in turn. Generated current could be improved either by light trapping or by increased device thickness. Considering fabrication costs and recombination losses, mechanically thin optically thick wafers are being focused on in terms of light trapping properties. Surface texturing among the other methods is an effective and more lasting technique in reducing reflections and improving light trapping. In order to maximize the absorption of light and the efficiency of the cell, various light trapping schemes have been proposed so far. In this study, texturing silicon (Si) wafer surface with periodic holes using two top-down fabrication techniques: Metal Assisted Etching (MAE) and Reactive Ion Etching (RIE) was focused on. Following the design of optical masks with patterns of different hole sizes and distributions, hole-textured surfaces with dimensions varying from micron scale to submicron scale were fabricated using both etching techniques. Hole-textured surfaces with desired hole depth values could be successfully fabricated. It was observed that surface having periodic holes with 4μm diameter, 5μm gap between holes and 8μm depth could result in 15.7% efficiency
Impact of oxygen partial pressure during Indium Tin Oxide sputtering on the performance of silicon heterojunction solar cells
No full text© 2022 Elsevier B.V.TCO has multiple functions in SHJ solar cell design, including the lateral transport of the photogenerated current and also providing high transparency and anti-reflective behavior. While superior performance lies behind concurrently addressing its multi-functions. Hence the balance between the optical and electronic properties of TCOs need careful engineering. In this study, RF sputtered Indium Tin Oxide films are analyzed in terms of their optical and electrical properties. The variations in the resistivity, mobility, carrier concentration, and specific contact resistivity of the film concerning oxygen partial pressure are discussed. Specific contact resistivity value for screen-printed low-temperature Ag contacts is decreased down to 0.4mΩ.cm2. The total increment on short-circuit current density is 0.6 mA/cm2 by reactive ITO sputtering. The photoconversion efficiency values of SHJ cells fabricated on 170 cm2 area with reactive sputtering is 20.56%, and optical loss analysis is carried out for the SHJ solar cells to quantify the performance of solar cells
Enhanced Passivation Properties of a-Si:H and Reactive ITO Sputtering for SHJ Solar Cells
No full textEnhancement of the conversion efficiency of silicon solar cells is crucial for the improvement of renewable electricity resources. The device properties such as minority carrier lifetime, series resistance, contact resistance and optical properties should be improved simultaneously to achieve higher photo conversion efficiencies. We use industry compatible processes flow to fabricate large-area silicon heterojunction (SHJ) solar cells combined with reactive ITO sputtering. The passivation properties of a-Si:H layer was improved by hydrogen plasma treatment resulting in a lower interface defect density and higher "H" content in the deposited thin a-Si:H layer. Moreover, carrier density, mobility and resistivity of ITO layer was analyzed and the best deposition condition of ITO is integrated to SHJ solar cell process sequence. Contact resistivity between ITO and low temperature silver paste was decreased by optimized drying and curing temperature parameters. In large- area SHJ solar cell, we have achieved conversion efficiency of 20.8%
A Study on Tetragonal-star Like Shaped Inverted Pyramid Texturing
No full textSurface texturing is one of the key process steps in solar cell fabrication. For an ideal surface texturing, surface recombination should be kept as low as possible while the light trapping property is improved. The formation of a random inverted pyramids is a good candidate with its improved light trapping properties compared to standard upright pyramid texturing and its reduced surface roughness compared to nanowire texturing resulting in reduced surface recombination velocity. In this work, we investigate a single step, lithography-free, Cu-assisted inverted pyramid texturing resulting in significantly reduced surface reflection on p-type Cz-Si. With the help of randomly distributed star-shaped inverted pyramid texturing on p-type Si, the weighted average reflection was reduced to 3% for p-type Si between 400-1000 nm. As a first cell trial, standard Al-BSF cells were fabricated using industrial process tools on p-wafer with star-shaped IPs. The low-cost, effective and repeatable nature of the developed single-step etching process has a high potential to replace surface texturing steps in the large-scale solar cell production cycle. Due to the implantation of star-shaped inverted pyramids to Al-BSF Si solar cell fabrication, short circuit current density was improved by more than 3.5%, resulting in 39.1mA/cm(2)
Simplified process flow for the fabrication of PERC solar cells with ion implanted emitter
No full textIon implanted PERC cells have already achieved power conversion efficiencies of about 20.0%. The process flows reported in the literature for the ion implanted PERC cells with commonly utilized Al2O3/SiNx rear passivation stack, which has the benefit of being less sensitive to surface roughness than SiO2/SiNx stack passivation, notably suffer from the additional process steps such as single side polishing and single side protection. Here, we present a simplified process flow for the fabrication of ion implanted PERC cells having Al2O3/SiNx stack passivation at the textured rear surface without any rear side processing, leading to a power conversion efficiency of 20% at large area. In this context, we show the sensitivity of solar cell efficiency to firing peak temperature, implantation dose, and Al2O3 thickness. The results of the present research will provide a basis for high efficiency implanted PERC cells with significantly reduced workload and cost. (c) 2021 Elsevier Ltd. All rights reserved
