32 research outputs found
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Silicon Heterojunction Solar Cell Characterization and Optimization Using In Situ and Ex Situ Spectroscopic Ellipsometry
The summary of this report is that: in situ SE gives insight into growth mechanisms and accurate layer thickness; (2) ex situ SE measures completed device structures to determine integrated optical properties; and (3) the combination of in situ and ex situ SE provides a powerful method for pinpointing the effects of processing changes in actual SHJ devices and guiding optimization
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Silicon Heterojunction Solar Cell Characterization and Optimization Using In Situ and Ex Situ Spectroscopic Ellipsometry: Preprint
We use in-situ and ex-situ spectroscopic ellipsometry to characterize the optical, electronic, and structural properties of individual layers and completed silicon heterojunction devices. The combination of in-situ measurements during thin film deposition with ex-situ measurements of completed devices allows us to understand both the growth dynamics of the materials and the effects of each processing step on material properties. In-situ ellipsometry measurements enable us to map out how the optical properties change with deposition conditions, pointing the way towards reducing the absorption loss and increasing device efficiency. We use the measured optical properties and thickness of the i-, n-, and p-layers in optical device modeling to determine how the material properties affect device performance. Our best solar energy conversion efficiencies are 16.9% for a non-textured, single-sided device with an aluminum back surface field contact on a p-type float zone silicon wafer, and 17.8% for a textured double-sided device on a p-type float zone silicon wafer
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SIMS Characterization of Amorphous Silicon Solar Cells Grown by Hot-Wire Chemical Vapor Deposition on Stainless Steel
This paper is intended to be an overview of some of the challenges that must be overcome when characterizing amourphous-silicon solar cell devices by the secondary ion mass spectrometry (SIMS) technique
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The use of electron channeling patterns for process optimization of low-temperature epitaxial silicon using hot-wire chemical vapor deposition
The authors demonstrate the first reported use of electron channeling patterns (ECPs) as a response for a statistical design of experiments process-optimization for epitaxial silicon. In an effort to fully characterize the new hot-wire chemical vapor deposition (HWCVD) method of epitaxial growth recently discovered at NREL, a large number of parameters with widely varying values needed to be considered. To accomplish this, they used the statistical design of experiments method. This technique allows one to limit the number of sample points necessary to evaluate a given parameter space. In this work they demonstrate how ECPs can effectively be used to optimize the process space as well as to quickly and economically provide the process engineer with absolutely key information
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Well-Passivated a-Si:H Back Contacts for Double-Heterojunction Silicon Solar Cells
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Real-Time Spectroscopic Ellipsometry as an In-Situ Diagnostic for Hot-Wire CVD Growth of Amorphous and Epitaxial Si
Real-time spectroscopic ellipsometry (RTSE) has proven to be an exceptionally valuable tool in the optimization of hot wire CVD (HWCVD) growth of both silicon heterojunction (SHJ) solar cells and thin epitaxial layers of crystal silicon (epi-Si). For SHJ solar cells, RTSE provides real-time thickness information and rapid feedback on the degree of crystallinity of the thin intrinsic layers used to passivate the crystal silicon (c-Si) wafers. For epi-Si growth, RTSE provides real-time feedback on the crystallinity and breakdown of the epitaxial growth process. Transmission electron microscopy (TEM) has been used to verify the RTSE analysis of thickness and crystallinity. In contrast to TEM, RTSE provides feedback in real time or same-day, while TEM normally requires weeks. This rapid feedback has been a key factor in the rapid progress of both the SHJ and epi-Si projects
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a-Si:H Grown by Hot-Wire CVD at Ultra-High Deposition Rates
We increase the deposition rate of growing hydrogenated amorphous-silicon (a-Si:H) by the hot-wire chemical vapor depositon (HWCVD) technique by adding filaments (two) and decreasing the filament(s) to substrate distance
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All-Hot-Wire Chemical Vapor Deposition a-Si:H Solar Cells
Efficient hydrogenated amorphous silicon (a-Si:H) nip solar cells have been fabricated with all doped and undoped a-Si:H layers deposited by hot-wire chemical vapor deposition (HWCVD). The total deposition time of all layers, except the top ITO-contact, is less than 4 minutes
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Small-Angle Neutron Scattering Studies of a-Si:H and a-Si:D
The heterogeneity of hydrogen and deuterium on the nanometer scale has been probed by samll-angle neutron scattering (SANS) from a-Si:H and a-Si:D films. Films were depsoited by two techniques, plasma-enhanced chemical vapor deposition (PECVD) and hot-wire chemical vapor deposition (HWCVD) using conditions that yield high quality films and devices
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Photoconductive Decay Lifetime and Suns-Voc Diagnostics of Efficient Heterojunction Solar Cells: Preprint
We report results of minority carrier lifetime measurements for double-sided p-type Si heterojunction devices and compare Suns-Voc results to Light I-V measurements on 1 cm2 solar cell devices measured on an AM1.5 calibrated XT-10 solar simulator