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Amorphous Silicon Compound Films for Surface Passivation and Antireflection Coating of Crystalline Silicon Solar Cells

Amorphous Silicon Compound Films for Surface Passivation and Antireflection Coating of Crystalline Silicon Solar Cells

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PETRES, Roman, 2010. Amorphous Silicon Compound Films for Surface Passivation and Antireflection Coating of Crystalline Silicon Solar Cells

@phdthesis{Petres2010Amorp-9487, title={Amorphous Silicon Compound Films for Surface Passivation and Antireflection Coating of Crystalline Silicon Solar Cells}, year={2010}, author={Petres, Roman}, address={Konstanz}, school={Universität Konstanz} }

eng Amorphous Silicon Compound Films for Surface Passivation and Antireflection Coating of Crystalline Silicon Solar Cells 2011-03-24T17:57:25Z 2010 Petres, Roman Chapter 1 gives an introductory overview of the current status of photovoltaics, with focus on crystalline silicon (c-Si) based technology. An essential contribution to the reduction of electricity generation costs at the solar module production level is to be expected mainly from reduced silicon consumption by using thinner wafers and/or employing cheaper silicon feedstock. Together with sufficient light trapping, the key factor to being able to exploit the combined cost reduction potential by using thin solar grade silicon wafers is the availability of very good and industrially applicable electronic surface passivation methods. That way, material quality makes almost no difference anymore when going down to wafer thicknesses of 30 µm from the current 150-200 µm. This gives the motivation for this work.<br />Chapter 2 gives an overview of the theoretical bases of surface passivation and antireflection coating and describes the methods and equipment used to characterize the layers created in this work.<br />While the µPCD was applied to obtain spatially resolved lifetime maps of the entire sample, the QSSPC was subsequently used to determine absolute values of the best areas that can be compared with the literature, as QSSPC is the established standard in c-Si photovoltaics.<br />The refractive index and thickness of the investigated dielectric films were measured by spectroscopic ellipsometry, and the chemical composition was analyzed by Fourier-Transformed Infrared Spectroscopy (FTIR) to investigate relations with the surface passivation and optical properties.<br />Chapter 3 explains the difference between growth and deposition as methods to obtain a film on top of a substrate and gives some examples of the dielectrics and their formation techniques which are most commonly used in current c-Si solar cell technology, with focus on SiOx and SiNx from thermal oxidation and Plasma Enhanced Chemical Vapor Deposition (PECVD), respectively.<br />Subsequently, the thin film formation technology by PECVD is described more detailed, and the particularities of the low-frequency (LF) direct-plasma PECVD reactor from Centrotherm, mainly used in this work, are outlined.<br />In chapter 4, the results of experiments with a-SiNx:H (SiNx) are presented. SiNx was solely deposited using the LF Centrotherm system, in contrast to SiCx.<br />Regarding deposition parameters, the influence of the gas flow ratio and wafer position in the horizontal boat position on the passivation and optical properties as deposited and after simulated contact co-firing were investigated.<br />As an approach to potentially reduce the costs of PECVD deposition by using cheaper precursor gases, the effect of a variation of the purity grade of ammonia used for the SiNx depositions was investigated on lifetime samples as well as solar cells. Finally, the long-term stability of the encapsulated solar cells was tested by temperature variation cycling as no clear difference between the different purity grades was detectable on the cell level between ammonia purity grades N50 (UHP), N36 and N20 (industrial grade, 99% purity).<br />Chapter 5 presents the experiments and results of a-SiCx:H (SiCx) depositions from methane and silane by both 13.56 MHz high-frequency and 40 kHz low-frequency PECVD, as well as experiments with a-SiCxNy:H (SiCxNy) deposited by low-frequency PECVD from either methane, ammonia and silane or ammonia together with an alternative silicon-containing precursor.<br />Resulting films were characterized by QSSPC lifetime measurements and thickness and refractive index evaluated by spectroscopic ellipsometry. The low-frequency deposited samples were later also subject to FTIR measurements to investigate their structure and chemical composition.<br />The best passivation was found for layers fabricated by the high-frequency PECVD with highest Si content, i.e. these layers were stoichiometrically close to amorphous silicon, with the passivation quality continuously decreasing with Si content. This trend changed after firing, with the highest effective lifetime being reached at a GFR of 6, whereas the passivation of the 4 ms sample almost completely degraded to 4 µs, which is in accordance with a-Si:H results, not able to withstand firing.<br />SiCx from LF-PECVD gave lower passivation for the as-deposited layers, but the best passivation after firing is better than for the films deposited by HF-PECVD within this work, and equals the best passivation by intrinsic SiCx reported by two authors. Petres, Roman 2011-03-24T17:57:25Z Amorphe Siliziumverbindungsfilme zur Oberflächenpassivierung und Antireflexbeschichtung von Kristallinen Siliziumsolarzellen deposit-license application/pdf

Dateiabrufe seit 01.10.2014 (Informationen über die Zugriffsstatistik)

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