Process Development for a High-throughput Fine Line Metallization Approach Based on Dispensing Technology

AbstractIn order to enhance prosperous dispensing technology towards an industrial application, besides a continuous process development, especially throughput rate has to be increased. In this study, paste rheology of two different dispensing pastes was transferred to CFD-simulation (CFD: Computational Fluid Dynamics) to investigate different nozzle geometries and print head designs. In the following, a single nozzle dispensing setup was used to verify simulative values by comparing them with those obtained from experimental investigations. Consequently, the single nozzle process was scaled to a parallel application, where a homogeneous pressure and flow distribution within the print head turned out to be crucial to achieve a homogeneous mass flow at all nozzles. In various iteration steps, the influence of fabrication tolerances especially concerning the nozzle geometry was isolated and print head designs were optimized based on CFD towards maximum process stability. Based on these results, a novel 10 nozzle fine line dispensing unit was designed and fabricated. Finally, successful cell production with resulting finger widths of less than 35μm could be demonstrated using the novel prototype

Optimization of the filament arrangement at constant radiant heat in HW-CVD for the preparation of compact µc-Si:H at high deposition rates

To obtain high deposition rates for microcrystalline silicon (muc-Si:H) with the Hot-Wire-CVD process under the constraint of a low substrate temperature of 250 degreesC, various combinations of hot wire arrangements and filament temperatures have been investigated. Raman and infrared spectroscopy and measurements of the dark and photo conductivity are used to evaluate the quality of the material. It is found that lowering the filament-substrate distance at low filament temperature results in a better material quality than higher filament temperatures at larger filament distances. High quality muc-Si:H was deposited at approximately 4 Angstrom s(-1) with filament temperatures of 1700-1750 degreesC and filament-substrate distances of 50-54 mm. (C) 2003 Elsevier B.V. All rights reserved

Improved deposition rate for µc-Si:H at low substrate temperature

Improving the deposition rate for microcrystalline silicon (mu c-Si:H) prepared by Hot Wire Chemical Vapour Deposition (HWCVD) under the constraint of a low substrate temperature is the subject of this study. The influence of the deposition pressure and various combinations of filament configuration and filament temperature oil the deposition rate and material quality was investigated. Raman and infrared spectroscopy and solar cell J-V parameters are used to evaluate the quality of the material. Low deposition pressures and low filament temperatures at low filament-substrate distances are most suitable to obtain high quality material at improved deposition rates. Deposition rates of 4 angstrom/s were achieved for high quality material at a substrate temperature of 250 degrees C. (c) 2005 Elsevier B.V. All rights reserved

Pilot-line processing of screen-printed Cz-Si MWT solar cells exceeding 17% efficiency

On the way to higher efficiencies, back contact solar cells are a promising alternative to conventional screen-printed solar cells. Especially, the MWT (metal wrap through) solar cell concept with only a few additional process steps compared to the conventional cell process is appropriate for a fast transfer to industry. The focus of this work is to change the conventional cell process as little as possible and to reduce the time-to-market. Hence, a MWT process with only three screen-printing steps and without efficiency losses is realized by combining the via and the solder pad metallization steps. In comparison with the conventional cell process the number of screen-printing steps is not increased and thus the costs for metallization rise only marginally due to somewhat increased paste consumption. In comparison to a previous approach the additional costs of the MWT process can be significantly reduced. A successful MWT process transfer from Fraunhofer ISE's Photovoltaic Technology Evaluation Center (PV-TEC) pilot-line to the pilot-line of ersol Solar Energy AG is shown. Mean cell efficiencies above 17% and maximum efficiencies of 17.3% are achieved for Cz-Si MWT solar cells within pilot-line production. Moreover, an efficiency gain compared to simultaneously processed, conventionally screen-printed solar cells of 0.3% absolute has already been reached. Furthermore, the influence of p-contact solder pads on the cell efficiency is analyzed in detail by current voltage (IV-) and photoluminescence (PL-) measurements within this work