Study on the Thermal Stress Distribution of Crystalline Silicon Solar Cells in BIPV

AbstractThe working temperature of BIPV modules is high than ground-mounted PV. Based on the theory of material mechanics and thermal stress analysis, the stress distribution of metallization interconnects system for crystalline silicon solar module in BIPV was studied for the first time. The shear stress and normal stress distribution of soldered structure for crystalline silicon solar cell under the thermal field were discussed. And the results show the stress distribution is not simply linear relationship as some results found. But there is a stress concentration at the edge, which was considered as the true reason that caused V-notch at the edge of soldered solar cell. The conclusions we got in this paper provide a theoretical basis for reliability of c-Si BIPV modules

Reactive Ink Metallization for Next Generation Photovoltaics

abstract: In order to meet climate targets, the solar photovoltaic industry must increase photovoltaic (PV) deployment and cost competitiveness over its business-as-usual trajectory. This requires more efficient PV modules that use less expensive materials, and longer operational lifetime. The work presented here approaches this challenge with a novel metallization method for solar PV and electronic devices. This document outlines work completed to this end. Chapter 1 introduces the areas for cost reductions and improvements in efficiency to drive down the cost per watt of solar modules. Next, in Chapter 2, conventional and advanced metallization methods are reviewed, and our proposed solution of dispense printed reactive inks is introduced. Chapter 3 details a proof of concept study for reactive silver ink as front metallization for solar cells. Furthermore, Chapter 3 details characterization of the optical and electrical properties of reactive silver ink metallization, which is important to understanding the origins of problems related to metallization, enabling approaches to minimize power losses in full devices. Chapter 4 describes adhesion and specific contact resistance of reactive ink metallizations on silicon heterojunction solar cells. Chapter 5 compares performance of silicon heterojunction solar cells with front grids formed from reactive ink metallization and conventional, commercially available metallization. Performance and degradation throughout 1000 h of accelerated environmental exposure are described before detailing an isolated corrosion experiment for different silver-based metallizations. Finally, Chapter 6 summarizes the main contributions of this work. The major goal of this project is to evaluate potential of a new metallization technique –high-precision dispense printing of reactive inks–to become a high efficiency replacement for solar cell metallization through optical and electrical characterization, evaluation of durability and reliability, and commercialization research. Although this work primarily describes the application of reactive silver inks as front-metallization for silicon heterojunction solar cells, the work presented here provides a framework for evaluation of reactive inks as metallization for various solar cell architectures and electronic devices.Dissertation/ThesisDoctoral Dissertation Materials Science and Engineering 201

Cost effective high efficiency solar cells

textTo make solar energy mainstream, lower-cost and more efficient power generation is key. A lot of effort in the silicon photovoltaic industry has gone into using fewer raw materials (i.e., silicon) and using more inexpensive processing techniques and materials to reduce cost. Utilizing thinner substrates not only reduces cost, but improves cell efficiency provided both front and back surfaces are well-passivated. In the current work, a kerf-less process is developed in which ultra-thin (~25 [mu]m), flexible mono-crystalline silicon substrates can be obtained through an exfoliation technique from a thicker parent wafer. These substrates, when exfoliated, have thick metal backing which provides mechanical support to the thin silicon and enables ease of processing of the substrates for device fabrication. Optical, electrical, and reliability characterization studies for completed cells show this technology’s compatibility with a heterojunction solar cell process flow. Building on the promising results achieved on exfoliated substrates, further optimization work was carried out. Namely, an improved cleaning process was developed to remove front surface contamination on textured surfaces of exfoliated, flexible mono-crystalline silicon. This process is very effective at cleaning metallic and organic residues, without introducing additional contamination or degrading the supporting back metal used for ultra-thin substrate handling. Spectroscopic studies were performed to qualitatively and quantitatively understand the efficacy of different cleaning procedures in order to develop the new cleaning process. Results of the spectroscopic studies were further supported by comparing the electrical performance of cells fabricated with different cleans. To replace silver as contact metal with a cheaper substitute like nickel or copper, patterning and etching processes are generally used. A low-cost alternative is proposed, where a reusable shadow mask with a metal grid pattern is kept in contact with the surface of the substrate in a plasma-enhanced chemical vapor deposition chamber during silicon nitride deposition. This leaves a patterned silicon surface for selective metal growth by direct electro-deposition. The viability of this process flow is demonstrated by fabricating diffused junction n[superscript+]pp[superscript+] monofacial and bifacial cells and electrically characterizing them. Investigation of the factors limiting the efficiency of the cells was carried out by lifetime measurement experiments.Electrical and Computer Engineerin

Delamination-and electromigration-related failures in solar panels—a review

The reliability of photovoltaic (PV) modules operating under various weather conditions attracts the manufacturer’s concern since several studies reveal a degradation rate higher than 0.8% per year for the silicon-based technology and reached up to 2.76% per year in a harsh climate. The lifetime of the PV modules is decreased because of numerous degradation modes. Electromigration and delamination are two failure modes that play a significant role in PV modules’ output power losses. The correlations of these two phenomena are not sufficiently explained and understood like other failures such as corrosion and potential-induced degradation. Therefore, in this review, we attempt to elaborate on the correlation and the influence of delamination and electromigration on PV module components such as metallization and organic materials to ensure the reliability of the PV modules. Moreover, the effects, causes, and the sites that tend to face these failures, particularly the silicon solar cells, are explained in detail. Elsewhere, the factors of aging vary as the temperature and humidity change from one country to another. Hence, accelerated tests and the standards used to perform the aging test for PV modules have been covered in this review

Flat-plate solar array project. Volume 5: Process development

The goal of the Process Development Area, as part of the Flat-Plate Solar Array (FSA) Project, was to develop and demonstrate solar cell fabrication and module assembly process technologies required to meet the cost, lifetime, production capacity, and performance goals of the FSA Project. R&D efforts expended by Government, Industry, and Universities in developing processes capable of meeting the projects goals during volume production conditions are summarized. The cost goals allocated for processing were demonstrated by small volume quantities that were extrapolated by cost analysis to large volume production. To provide proper focus and coverage of the process development effort, four separate technology sections are discussed: surface preparation, junction formation, metallization, and module assembly

Väriaineherkistetyt nanorakenteiset ja orgaaniset aurinkosähkökennot: tekninen kirjallisuuskatsaus ja alustavia kokeita

The solar electricity is presently a rapidly growing but often relatively expensive renewable energyform. Recently however, new molecular photovoltaic (PV) materials have been developed, whichcould enable a production of low-cost solar cells in the future. The thesis begins with a discussion of the current status of the PV technology and a shortintroduction to the different PV technologies and to the basics of photovoltaics. The dye-sensitized solar cell (DSSC) is an electrochemical solar cell where light absorption occursby dye molecules attached to a nanostructured TiO2 electrode. An introduction to the DSSC is givenincluding a short description of the operating principle of the cell and a discussion of the physicaland chemical processes behind it. A systematic literature review is done on the materials and mostessential preparation methods of the standard DSSC. The performance of the DSSC is reviewed in terms of the energy conversion efficiency and the longtermstability. The important directions of development are the transition from glass substrates toplastic foils and from batch processing to continuous processing as well as the use of solid stateelectrolytes. The glass-based DSSC technology is on the verge of commercialization and themanufacturing cost estimates for the technology are close to the projected costs of other PVtechnologies. The purely organic solar cells are discussed individually beginning with the discussion of thefundamentals of organic photovoltaics and an introduction of different types of organic photovoltaicmaterials including semiconducting polymers, dyes, pigments and liquid crystalline materials. Areview is done on the performance results of organic solar cells categorizing the cells by their devicearchitecture. The development of the organic PV materials is still at an early stage and no clearlyoutperforming materials or cell structures have yet emerged. Experimental results are reported including a demonstration of the dye-sensitization with a naturaldye as well as a preparation and testing of a series of ruthenium-dye based DSSCs. An efficiency of0.6% at about 600 W/m2 solar illumination was obtained for the DSSCs in outdoor measurements.Aurinkosähkö on tällä hetkellä nopeasti kasvava mutta usein verrattain kallis uusiutuvaenergiamuoto. Viime aikoina on kuitenkin kehitetty uusia molekulaarisia aurinkosähkömateriaaleja,jotka voivat mahdollistaa tulevaisuudessa halpojen aurinkosähkökennojen tuotannon. Työn alussa käsitellään aurinkosähkön nykytilaa ja luodaan lyhyt katsaus eriaurinkosähköteknologioihin ja aurinkosähkön perusteisiin. Väriaineherkistetty aurinkokenno (väriainekenno) on valosähkökemiallinen aurinkokenno, jossavalon absorptio tapahtuu nanorakenteisen TiO2 -elektrodin pintaan kiinnittyneidenväriainemolekyylien avulla. Työssä esitellään väriainekennon toimintaperiaate ja tarkastellaan sentaustalla olevia fysikaalisia ja kemiallisia prosesseja, sekä tehdään järjestelmällinenkirjallisuuskatsaus perusväriainekennon materiaaleihin ja tärkeimpiin valmistusmenetelmiin. Väriainekennon suorituskykyä tarkastellaan energian konversion hyötysuhteen japitkäaikaisstabiilisuuden osalta. Tärkeitä kehityssuuntia ovat siirtyminen lasisubstraateistamuovikalvoihin ja vaiheittaisesta valmistusprosessista jatkuvaan prosessiin sekä kiinteidenelektrolyyttien käyttö. Lasisubstraattiin perustuva väriainekennoteknologia on kaupallistumisenkynnyksellä ja sen valmistuskustannusarviot ovat lähellä muiden aurinkosähköteknologioidenkustannusennusteita. Puhtaasti orgaanisia aurinkosähkökennoja tarkastellaan erikseen alkaen orgaanistenaurinkosähkömateriaalien fysikaalisista perusteista. Tämän jälkeen esitellään erilaiset orgaanisetaurinkosähkömateriaalit, joihin kuuluu puolijohtavia polymeerejä, väriaineita, pigmenttejä janestekiteisiä materiaaleja, sekä tehdään katsaus orgaanisten kennojen tuloksiin luokitellen kennotniiden rakenteen mukaan. Orgaanisten aurinkosähkömateriaalien kehitys on vielä alkuvaiheessa eikäselkeästi suorituskyvyltään muita parempia materiaaleja ja kennorakenteita ole vielä ilmennyt. Lopuksi esitetään kokeelliset tulokset väriaineherkistyksen havainnollistamisesta luonnonväriaineella sekä ruteeni-väriaineeseen perustuvien väriainekennojen valmistuksesta ja testauksesta.Ulkomittauksissa 600 W/m2 auringonvalossa saavutettiin väriainekennojen hyötysuhteeksi 0.6%

Improving the Performance and Durability of Metal Contacts in Crystalline Silicon Solar Cells Using Advanced Characterization

Solar energy is one of the fastest growing forms of energy generation due to its low cost, lack of emissions, minimal maintenance, and excellent durability. However, like any other technology, it is also not free from defects and degradation, which limit its performance in the real world. Most of the degradation is related to metal contacts, which also happens to be one of the most expensive items in manufacturing, comprising almost half of the cost of converting a silicon wafer into a photovoltaic (PV) cell. Therefore, studying contact degradation to make them reliable and free of defects is the key to achieving high energy yields. High efficiency PV modules that are both cheap and reliable with an extended lifetime ultimately reduce the levelized cost of energy. This study aims to characterize contact degradation in solar cells to identify the root causes of performance losses and develop alternate solutions to metallization. Electrical and optical characterizations were performed on both accelerated-aged and field-exposed solar cells and modules to look for specific performance losses. Furthermore, materials characterization was performed on selected samples to understand the potential root causes and factors affecting the degradation. Unencapsulated solar cells mainly consisting of newer cell technologies and metallization were exposed to acetic acid to simulate field conditions and understand the effect on contact corrosion. Finally, a low-cost novel contact technology called the transferred foil contact was developed that can be used as the back contact of a highly efficient silicon heterojunction solar cell, to minimize recombination, and potentially combine cell metallization and interconnection. An overview of the solar energy history and current state-of-the-art is first discussed, followed by a chapter on solar cell device physics and contact technology. The following chapters discuss the different degradation mechanisms in terms of the process-structure-properties relationships of the PV materials

Toward The Development Of Printable Perovskite Solar Cells

PSCs have become a significant performer in third generation photovoltaics with power conversion efficiency, greater than 22% for active areas less than 1 cm2. However, with efficiency improvement, concerns regarding the operational stability and industrial production firstly resolved to grow into commercially viable PSCs. To address above stated issues most stable, yet efficient Monolithic PSCs (mPSCs) are structured. The mPSCs are having compact TiO2, mesoporous TiO2, mesoporous ZrO2, and mesoporous carbon electrode layers in optimal thicknesses on the FTO substrate. Fabrication protocol for all the layers which is easily scalable for large area mPSCs manufacturing is highly required. Furthermore top carbon electrode materials those are stable and behaves as protective casing to make PSCs stable has also been highly desired. Hence, in this project our aim is to optimize top carbon layer and study photophysical processes inside the mPSCs. This research work is mainly divided into three parts. The first part of the dissertation described carbon film fabrication by screen printing technique and their investigation at different annealing temperature . Influence of annealing temperatures on the electrical, morphological and structural properties of the carbon film has been discussed. It is shown that a low annealing temperature is good for better adherence of the conductive carbon films, however, temperatures higher than 300°C are required to produce efficient mPSCs. A sintering temperature of 400°C showed the highest device efficiency of 13.2%. It is important to correlate all the physical properties/processes taking place in the mPSCs to gain a deeper understanding of mPSCs operation: What is the role of the contacts? What limits the efficiency of existing perovskite solar cells? How many charge carriers are there in the cell under operating condition. Hence, in second part, Electrochemical Impedance spectroscopy (EIS) spectrum has been described, which is performed on the mPSCs having highest efficiency during previous experiments. The EIS spectrum of mPSCs quantitatively explains the role of contacts, layers, charge generation, drift and diffusion of charge carriers and recombination. This would further provide insight into the performance-limiting physical processes of mPSCs. The microstructure or morphology of the perovskite crystals inside mesoporous TiO2 and mesoporous ZrO2 have significant effect on the mPSCs performance and stability. Therefore, to achieve higher mPSCs device performance, one-dimensional microrods (4mm-5mm) of PbI2 and CH3NH3PbI3 (MAPbI3) is fabricated in the 3rd part. These microrods consist of unique structural and morphological properties which are grown at room temperature. The XRD and TEM analyses confirm the existence of strong interactions between different stable groups in the crystals. The morphological studies approve crack free morphology of PbI2 and MAPbI3 micro-rods. The above results are expected to have a big effect on solar cell and photo-detection industry by fostering improvement of thin-film opto-electronic devices

Long term stability of silicide based thermoelectric materials and modules

Silicide-based thermoelectric generators are potential candidates for waste heat recovery at temperatures below 500  C. For the last two decades, the conversion efficiency of modules based on n-type magnesium silicides and p-type higher manganese silicide has improved significantly. However, the conditions in which thermoelectric generators operate (for example, remote areas in the oil, gas, and telecommunication industries, in automobiles, etc.) are harsh (corrosive, for example) and hostile (due to thermal instability). In this project, there was much focus on the stability of the thermoelectric modules, with special interest given to oxidation of the thermoelectric materials and module stability. The thermal oxidation studies were conducted on higher manganese silicide alloys; the studies mainly investigated the effect of the alloys’ composition, consolidation techniques and the operational atmosphere’s effect on their oxidation potential. Moreover, the choice of matching electrodes and good bonding technology for the module assembly was the ultimate step before finally testing the actual performance and stability of the module over an extended period. The thorough oxidation studies conducted in this thesis revealed the importance of different production processes for the higher manganese silicide thermoelectric materials on the oxidation robustness of the alloys. The study showed that the purity (fewer impurities) of the raw elements and optimal doping level are among the key factors for the alloys to resist oxidation by growing a protective SiO2 protective oxide layer. Moreover, it was also shown that powder consolidation by spark plasma sintering produced stronger bulk pellets, and mechanical strength played a key role in passive oxidation. During the module’s contacts design, silver electrodes and solid liquid interdiffusion bonding technology were used. The contact resistance of the assembled modules were measured using an automated point contact measurement test rig. On the magnesium silicide the specific contact resistance was on average 0.17 m cm2 with 2.1% standard deviation. The higher manganese silicide’s contact interface, on the other hand, the results were dispersed along the bond, where 0.07 m cm2 was the lowest value and 1.12 m cm2 the highest (81.3% standard deviation). Finally, the module stability was investigated by testing the performance of the assembled modules. The tested modules produced up to 7.4mW/cm2 power density at 400  C and sustained more than 300 thermal cycles. The gradual degradation was found to mainly originate from the mechanical failure of the contact interfaces and oxidation of the n-type magnesium silicide relative to the p-type material. Applying a high-temperature coating did not reduce the degradation rate, which showed that it would be better to encapsulate the modules to count-act the effect of oxidation.publishedVersio

From Field to Failure: Detecting and Understanding Reliability Defects in Crystalline Silicon Photovoltaics

Severe pollution levels and the growing influence of climate change have shown that dirty energy sources need renewable and sustainable replacements. The field of photovoltaics (PV) has grown substantially over the years from a niche space solar market to a commodity in large part due to improvements in reliability. Reliability of all materials in a PV module must be considered. The industry has seen an explosion of innovation in cell interconnection technologies with significant market penetration in the past several years. These emerging, less mature technologies require more reliability information to guide improvements. Degradation studies of long-term outdoor exposure and accelerated stress testing provide the samples, but a comprehensive characterization suite is necessary for impactful results. The state of the art for characterization is highly valuable yet incomplete. This work presents a multiscale, multicomponent process that provides information on device physics, polymer performance, thermal signatures, chemical composition, and degradation mechanisms, as well as advancements in electrical performance and defect localization. A comprehensive characterization suite is proposed which expands upon conventional one-sun current-voltage (I-V) and high injection electroluminescence (EL) imaging to multi-irradiance I-V, suns-Voc, multi-injection EL imaging and analysis, IR thermography, and UV fluorescence imaging. A database of over 1000 I-V curve, high-injection EL image pairs is presented for public use. An analysis and measurement technique is developed using EL images at multiple injection levels to non-destructively extract dark I-V curves for each cell. These curves can be analyzed to extract device properties. A machine learning model is developed using annotated EL images for automated defect detection. The training set of 17,064 cell EL images is publicized for the industry\u27s benefit. While applicable to all module technologies, the focus of this work is on applying this expansion on characterization to studying interconnection and contact degradation. Several interconnection technologies are studied with varying results. Each technology is shown to have distinct advantages and disadvantages with respect to performance and reliability. Modules are studied that have undergone accelerated tests and outdoor exposure. It is shown that full interconnection separation influences degradation differently depending on location of failure, though requires many failures before significant performance losses are evident. In another study, a model is developed for the mechanism behind front contact corrosion in damp heat degraded modules. A coring process is developed to extract cell samples which allows materials characterization. Results demonstrate that the primary mechanism is based on Sn diffusion from interconnection ribbons via acetic acid and moisture. One study examines a system of modules exposed in Florida for 10 years showing rear interconnect corrosion at the Ag/solder interface. Intermetallic compound formation led to reduced carrier transport and contact embrittlement leading to fatigue failure susceptibility. Another study investigates four different interconnection technologies before, during, and after stages of different accelerated stress protocols. Five-busbar ribbon, shingled, soldered wire, and laminated wire technologies underwent mechanical loading, humidity freeze, damp heat, and thermal cycling tests. Laminated wire performed the best overall though showed some features in EL imaging that have not yet been published. In the final study presented, a system of heterojunction modules from a system in Florida after 10 years exposure show resistive degradation. Device and materials characterization shows recombination and resistive losses, with resistive losses due corrosion at the intrinsic a-Si/c-Si interface