Laser Micro-Processing in Solar Cell Production

Mayerhofer, R.; Müllers, Ludger; Becker, Alejandro

doi:10.1109/wcpec.2006.279356

Cited by 5 publications

(3 citation statements)

References 2 publications

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“…14, the dielectric layer is opened in the center in order to allow for a direct contact of the p‐metallization to the silicon substrate. After stripping the mask in aqueous alkaline solution, the via‐holes are drilled with a high speed laser drilling process 12, 15, reaching a drilling rate of around 5000 via‐holes per second. The laser damage is removed with an appropriate damage etch (IV) (see Ref.…”

Section: Process Sequencementioning

confidence: 99%

“…A single wet thermally grown silicon dioxide layer serves both as diffusion barrier for the definition of the interdigitated rear side diffusion and passivation of the region between the n + ‐area and the p + ‐contact denoted as “gap region” in the following. For the fabrication of the via‐holes a high‐speed laser drilling process described elsewhere 12 is applied. The cell structure features a selective emitter structure: a highly doped emitter at the via‐holes and the rear side, allowing for a low via‐hole resistivity as well as a low resistivity contact to screen‐printed pastes, and a moderately doped front side emitter exhibiting high quantum efficiency in the low wavelength range.…”

Section: Introductionmentioning

confidence: 99%

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Screen‐printed Emitter‐Wrap‐Through solar cell with single step side selective emitter with 18.8% efficiency

Mingirulli

Stüwe

Specht

et al. 2011

Progress in Photovoltaics

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A fabrication process for Emitter‐Wrap‐Through solar cells on monocrystalline material with high quality gap passivation by wet thermal silicon dioxide is investigated. Masking and structuring steps are performed by screen‐printing technology. Via‐holes are created by an industrially applicable high‐speed laser drilling process. The cell structure features a selective emitter structure fabricated in a single high temperature step: a highly doped emitter at the via‐holes and the rear side, allowing for a low via‐hole resistivity as well as a low resistivity contact to screen‐printed pastes, and a moderately doped front side emitter exhibiting high quantum efficiency in the low wavelength range. Therefore a novel approach is applied depositing either doped or undoped PECVD silicon dioxide layers on the front side. It is shown that doping profiles advantageous for the EWT‐cell structure can be achieved. The screen‐printed aluminum paste is found to penetrate the underlying thermal dioxide layer at appropriate contact firing conditions leading to a zone of high recombination in the overlap region of aluminum and silicon dioxide. It is shown that conventional PECVD‐anti‐reflection silicon nitride acts as effective protection layer reducing the recombination in this region. Designated area conversion efficiencies up to 18.8% on FZ material are obtained applying the single step side selective emitter fabrication technique. Copyright © 2010 John Wiley & Sons, Ltd.

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Section: Process Sequencementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Screen‐printed Emitter‐Wrap‐Through solar cell with single step side selective emitter with 18.8% efficiency

Mingirulli

Stüwe

Specht

et al. 2011

Progress in Photovoltaics

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“…radiated material, thus strongly influencing removal rates and heat affected zones. As a rule of thumb, the longer a single pulse, the higher are the removal rates [3] as long as the power density is above the threshold for melting and vaporization.…”

Section: The Question Of Wavelengthmentioning

confidence: 99%

Power Is (Not) Everything

Mayerhofer¹

2009

Laser Technik Journal

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The variety of different laser sources, either a brand new product or a derivate of already existing concepts is growing almost every day. Even an experienced application guy like me struggles more and more to find the appropriate laser for a specific application in the first shot. It is out of question, that it is more difficult for our customers who have not been so close to the evolution process of lasers, penetrating more and more areas of industrial production. Thus, this article is intended to give a broad overview on the fundamentals of laser material processing in order to help finding suitable laser properties for your application quickly. The influence of the most important parameter in laser material interaction, the amount of laser power, necessary for specific industrial applications is outlined. The Question of WavelengthThe wavelength of the laser beam is a very important parameter, and often raises wrong expectations. The wide-spread opinion is, that just through the reduction of the wavelength from near-infrared (NIR, i.e. 1064 nm) into ultraviolet (UV, i.e. 355 nm), immediately both heat affected zone and processing spot size are reduced at the same ratio. However, for visibly grey metals the absorption behavior is fairly constant within this frequency range. On the other side, the absorption in the laser induced vapor or plasma plume above the processing area shows a minimum for green (i.e. 532 nm lasers) increasing towards shorter and longer wavelengths [1]. This can lead to power losses and scattering of the beam, affecting both ablation rate and spot sizes negatively. Together with the general loss in output power through the frequency conversion and significantly increased complexity of the system, there are not many reasons left to apply UV-wavelength instead of NIRlasers on metals.A similar myth has been created around semiconductor materials, where dramatic reductions in heat affected zones, and thus much better application results, have been taken for granted through the use of shorter wavelengths. For silicon it is true, that the absorption length for low power density light at room temperature is reduced by two orders of magnitude. However, these measurements cannot be generically applied to laser processing, where focused, high power density nanosecond-pulses will raise the surface temperature of the irradiated area above melting point even before the laser pulse reaches its maximum energy. As soon as a semiconductor is molten, its absorption behavior is comparable to a metal with very short absorption depths. Application examples on silicon, that do not show a significance of the wavelength reduction from NIR to UV can be found in solar applications, like edge isolation [2] and wafer drilling. Apparently, other parameters like pulse length and processing strategy are much more dominant than the influence of the laser wavelength.Looking at plastic materials, especially thermoplastic polymers, the wavelength of the laser beam plays an important role for the initial absorption. Strong...

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