Academic literature on the topic 'QSSVOC'

In a multicrystalline silicon (mc-Si) wafer, trapping effects frequently occur in the carrier lifetime measurement based on the quasi-steady-state photoconductance (QSSPC) technique. This affects the accurate measurement of the carrier lifetime of an mc-Si solar cell by causing distortions at a low injection level close to the Pmax point. Therefore, it is necessary to understand this effect and effectively minimize the trapping-center density. In this study, the variations in the minority carrier-trapping effect of hydrogen at different annealing temperatures in an mc-Si were observed using QSSPC, time-of-flight secondary ion mass spectroscopy, and atom probe tomography. A trapping effect was confirmed and occurred in the grain boundary area, and the effect was reduced by hydrogen. Thus, in an mc-Si wafer, effective hydrogen passivation on the grain area and grain boundary is crucial and was experimentally proven to minimize the distortion of the carrier lifetime.

This review begins with a brief survey of the observational constraints on the standard big bang cosmology, pointing out that the various limits leave a very narrow window in the parameter space of plausible models. There is thus a strong case for alternative cosmologies. The rest of the review concentrates on one alternative, the quasi steady state cosmology (QSSC) and summarises the recent work on this model. This includes, the theoretical formulation and simple exact solutions of the basic equations, their relationship to observations, the stability of solutions and the toy model for understanding the growth of structures in the universe.

Analytical solutions for radiation-dominated phase of Quasi-Steady-State Cosmology (QSSC) in Friedmann–Robertson–Walker models are obtained. We find that matter density is positive in all the cases [Formula: see text]. The nature of Hubble parameter (H) in [Formula: see text] is discussed. The deceleration parameter [Formula: see text] is marginally less than zero indicating accelerating universe. The scale factor [Formula: see text] is graphically shown with time. The model represents oscillating universe between the above-mentioned limits. Because of the bounce in QSSC, the maximum density phase is still matter-dominated. The models represent singularity-free model. We also find that the models have event horizon i.e. no observer beyond the proper distance [Formula: see text] can communicate each other in FRW models for radiation-dominated phase in the frame work of QSSC. The FRW models are special classes of Bianchi type I, V, IX spacetimes with zero, negative and positive curvatures, respectively. Initially i.e. at [Formula: see text], the models represent steady model. We have tried to show how a good fit can be obtained to the observations in the framework of QSSC during radiation-dominated phase. The present model is free from singularity, particle horizon and provides a natural explanation for the flatness problem. Therefore, our model is superior to other models.

We examine the possible consistency of the quasi-steady state model with the newly discovered SNe Ia . The model assumes the existence of metallic dust ejected from the SNe explosions, which extinguishes light travelling over long distances. We find that the model shows a reasonable fit to the data, which improves if one take account of the weak gravitational lensing effect of the SNe which have been observed on the brighter side.

The aim of this paper is to study the effect of erbium oxide (Er2O3) on porous silicon (PS) wafers used for photovoltaic application. An immersion of PS wafers in Er2O3 solution can be used to enhance light trapping and form an efficient surface by passivation process. PS was prepared by the stain-etching method and doped by Er species. In fact, the topography was investigated by the scanning electron microscope (SEM). In addition, the spectral behaviors of the reflectivity and the photoluminescence were discussed. The dependence of minority carrier lifetime was evaluated by means of the Quasi-Steady-State Photoconductance technique (QSSPC). Besides, an enhancement in lifetime was observed. A framework is provided for estimating an efficiency improvement in studied films which will help to guide the development of improved energy-efficient.

Thin-film solar cells on glass substrates are likely to have a bright future due to the potentially low costs and the short energy payback times. Polycrystalline silicon (poly-Si, grain size > 1 pm) has the advantage of being non-toxic, abundant, and long-term stable. Glass as a substrate, however, limits the processing temperatures to ~600??C for longer process steps. Films with large grain size can be achieved by solid phase crystallisation (SPC), and especially by solid phase epitaxy (SPE) on seed layers, using amorphous silicon deposited at low temperatures as a precursor film. With SPC and SPE, the amorphous silicon film is typically crystallised at ~600??C over hours. During this anneal at atmospheric pressure -depending on the properties of the amorphous silicon film- ambient gas can percolate the film and can negatively affect the crystallisation. In this work, a high-vacuum anneal chamber was designed and built to allow the in-situ crystallisation of amorphous silicon films deposited on glass in a PECVD cluster tool. An important aspect of the design was the comfortable and safe operation of the vacuum anneal chamber to enable unattended operation. This was realised by means of a state-of-the-art, programmable temperature controller and a control circuit design that incorporates various safety interlocks. The chamber interior was optimised such that a temperature uniformity of 2-3K across the sample area was achieved. The chamber was calibrated and tested, and SPC and SPE samples were successfully crystallised. In initial SPC crystallisation experiments with solar cell structures, after post-deposition treatments, a 1 -sun open-circuit voltage of 465 mV was obtained, similar to furnace-annealed samples. In initial experiments with SPE solar cell structures, difficulties regarding the characterisation of the unmetallised solar cells with the quasi-steady-state open-circuit voltage method (QSSVOC) were encountered after post-deposition hydrogen treatment. A possible explanation for these difficulties is the contact formation with the metal probes. Furthermore, limiting factors of the QSSVOC method for the characterisation of unmetallised cells with high contact resistance values were investigated and, additionally, the accuracyof the QSSVOC setup was improved in the low light intensity range.

This thesis deals with a lifetime measurement of current carriers in silicon solar cell structures. In the first chapter there is a description of several recombination models and their participation at a final effective lifetime value. By using these recombination models in a computer simulation it is possible to receive approximate evaluation of some important silicon solar cell structure parameters. The PC1D simulation program was used for this thesis. For the lifetime measurement of real test-wafers two methods were used: QSSPC (quasi-steady-state photoconductance) and MW-PCD (microwave photoconductance decay). There is a detail description of these methods, used measurements machines and differences between both of them in the chapter four. The main objective of the thesis is mentioned in the last chapter, which is mainly focused on a chemical passivation of silicon wafers and deals with a problem of post-passivation wafer cleaning. There are three passivation techniques mentioned: the iodine in ethanol solution, the iodine and polymer in ethanol solution and the quinhydron in methanol solution. In two cases a results, that are adequate to return the tested wafers in the manufacture process, were achieved.

Tese de mestrado integrado em Engenharia da Energia e do Ambiente , apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2011
As medidas dos tempos de vida efectivos, dos portadores minoritários de carga, dão uma informação importante na caracterização de materiais em aplicações fotovoltaicas. Estas medidas permitem que as wafers de má qualidade sejam identificadas e removidas das linhas de produção numa fase inicial do processo de fabrico de células solares. Os dois instrumentos de medida utilizados, WCT-120 da Sinton Instruments e o WT-1000 da Semilab Semiconductors, permitem medir o tempo de vida efectivo dos portadores minoritários e são baseados em medidas da fotocondutância. Por essa razão, estão sujeitos aos efeitos dos centros de recombinação das wafers, levando a medidas aparentes que não representam o tempo de vida dos portadores minoritários em volume. No sentido de mitigar o efeito de recombinação à superfície, utilizam-se métodos de passivação. Estes métodos reduzem a velocidade de recombinação à superfície. Se o método de passivação for eficaz, o tempo de vida efectivo medido é aproximadamente igual ao tempo de vida em volume. Com o objectivo de comparar os dois sistemas, fizeram-se medidas de tempos de vida por variação de espessura das amostras e por passivação da superfície. Em ambos, estimou-se a velocidade de recombinação à superfície. Pela comparação com uma medida de referência, concluiu-se que ambos os sistemas estão operacionais e que dão valores confiáveis para medidas em wafers de silício monocristalino. Menores discrepâncias entre os dois sistemas são obtidas quando se passiva a superfície das amostras.
Effective lifetime measurements of minority carriers are immensely important in material characterization for photovoltaic applications. These measurements help us in identifying low quality wafers, and therefore removing them from the production line in the initial stages of the manufactoring process. The two instruments used, Sinton Instruments WCT-120 and Semilab Semiconductors WT-1000, are able to measure effective lifetime based on photoconductance measurements. Due to this fact, these measurements are influenced by wafer recombination centers which lead to apparent lifetime measurements that do not represent the bulk lifetime. In order to minimize the surface recombination effects, methods of passivation are used. These methods reduce the surface recombination velocity. If these methods of passivation are effective, the lifetime measured is approximate to bulk lifetime. With the final goal of comparing the two instruments, measurements of lifetime were obtained varying the thickness of the samples and also passivating the surface. Surface recombination velocity was estimated in both cases. Through the use of a reference measurement, it was concluded that both instruments were operational and return trustable values of lifetime measurements for monocrystalline silicon wafers. Fewer discrepancies between the two instruments are obtained when surface passivation is used.

Tese de mestrado integrado, Engenharia da Energia e Ambiente, Universidade de Lisboa, Faculdade de Ciências, 2020
As principais fontes de produção de energia estão, nos dias de hoje, associadas a problemas de impacto ambiental, devido à queima de combustíveis fósseis como o petróleo e o carvão. Como forma de mitigar esses problemas, a exploração de fontes alternativas de energia, como a renovável, aumentou. Entre as várias fontes de energia renovável destaca-se a energia solar devido ao seu fácil acesso, tornando-se assim um meio energético com grande interesse. E, por isso, de modo a obter um aproveitamento máximo da energia solar, têm surgido vários métodos de conversão desta em energia elétrica, através de dispositivos fotovoltaicos. A passivação das superfícies das células de silício é importante para se obter elevada conversão de energia, permitindo reduzir a recombinação dos portadores de carga minoritários. A técnica mais utilizada para passivação de células solares é o crescimento de dióxido de silício (𝑆𝑖𝑂2) através de vários tipos de oxidação: térmica e química. Passivaram-se amostras através destes dois tipos de oxidação variando-se a temperatura (𝑇𝑜𝑥𝑖) e o tempo (𝑡𝑜𝑥𝑖) de oxidação de crescimento das camadas de 𝑆𝑖𝑂2 de forma a determinar o impacto nos tempos de vida, e por sua vez na recombinação. Variou-se a 𝑇𝑜𝑥𝑖, para o processo térmico de 800ºC a 900ºC e o 𝑡𝑜𝑥𝑖 de 60min a 120min. Para o processo de oxidação química variou-se a 𝑇𝑜𝑥𝑖 entre 25ºC (temperatura ambiente) e 80ºC e o 𝑡𝑜𝑥𝑖 de 30min a 180min. Estas variações permitem traçar um perfil aperfeiçoado da qualidade de passivação, através das medidas resultantes dos tempos de vida. Para ambos os processos de oxidação, observa-se que com o aumento da temperatura e do tempo de oxidação atingem-se melhores qualidades de passivação. De modo a acrescer o desempenho da célula, utilizam-se contactos seletivos, optando-se pelo dióxido de titânio (𝑇𝑖𝑂2), com base em estudos anteriores, devido aos desvios otimizados das suas bandas de condução e valência. Os melhores resultados antes e após a deposição da camada seletiva em ambas as faces da amostra foram os da passivação por oxidação térmica, obtendo-se valores de tempo de vida de 101,75μs.
The main sources of energy production are, today, associated with problems of environmental impact, due to the burning of fossil fuels such as oil and coal. As a way of mitigating these problems, the exploration of alternative energy sources, such as renewable, has increased. Among the various sources of renewable energy, solar energy stands out due to its easy access, thus becoming an mean of energy with great interest. And, therefore, in order to obtain a maximum use of solar energy, several methods of converting it into electrical energy, through photovoltaic devices have emerged. The passivation of the surfaces of the silicon cells is important to obtain high energy conversion, allowing to reduce the recombination of minority charge carriers. The most used technique for passivating solar cells is the growth of silicon dioxide (𝑆𝑖𝑂2) through various types of oxidation: thermal and chemical. Samples were passivated through these two types of oxidation by varying the temperature (𝑇𝑜𝑥𝑖) and the time (𝑡𝑜𝑥𝑖) of oxidation for the growth of the 𝑆𝑖𝑂2 layers in order to determine the impact on the lifetime and, thus, recombination. The 𝑇𝑜𝑥𝑖 was varied for the thermal process from 800ºC to 900ºC and the 𝑡𝑜𝑥𝑖 from 60min to 120min. For the chemical oxidation process, the 𝑇𝑜𝑥𝑖 varied between 25ºC (room temperature) and 80ºC and the 𝑡𝑜𝑥𝑖 from 30min to 180min. These variations make it possible to draw an improved profile of the passivation quality, through the measures resulting from the lifetime. For both oxidation processes, it is observed that with the increase in temperature and oxidation time, better passivation qualities are achieved. In order to increase the performance of the cell, selective contacts are used, opting for titanium dioxide (𝑇𝑖𝑂2), based on previous studies, due to the optimized deviations of its conduction and valence bands. The best results before and after deposition of the selective layer on both sides of the sample were those of passivation by thermal oxidation, obtaining lifetime values of 101.75μs.