R2M-SI

Roll to Module processed Crystalline Silicon Thin-Films for higher than 20% efficient modules

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 Obiettivo del progetto (Objective)

'The current technologies to produce photovoltaic modules exhibit features, which prevent cost-reduction to below 0,5€/Wp: - Sawing/Wafering and Module assembly is costly and material intensive for wafer solar cells - Efficiency is comparatively low for classical thin-film solar cells (CdTe, CIS, a-Si/µc-Si, dye, organic). One approach to avoid both disadvantages is the so-called crystalline Si thin-film lift-off approach, where thin c-Si layers are stripped from a silicon wafer. This approach has the potential to reach > 20% efficient solar cells, however handling issues stop quick progress so far. The basic idea of the current project is to enable the use of lift-off films in a nearly handling-free approach, to avoid limitations by handling issues. The technological realization has the following key features and steps: - Continuous separation of a very thin (< 10 µm) c-Si foil from the circumference of a monocrystalline silicon ingot - Attachment to a high-temperature stable substrate of large area (e.g. graphite, Sintered Silicon, or ceramics), which can also serve as module back side. - High-temperature re-organisation of the silicon foil followed by in-situ epitaxial thickening (~40 µm base thickness) in an in-line chemical vapour deposition reactor, including pn-junction formation - Processing of high-efficiency solar cells and formation of integrated interconnected high-voltage modules - Encapsulating into a module (glass / encapsulant only if needed) The resulting module to be demonstrated in R2M-Si has a cost potential around 0.55 €/Wp, at 18% module efficiency and thus low Balance-of-System cost. Future enhanced R2M-Si modules can exceed even 20% efficiency, at costs below 0.5 €/Wp. The project shall demonstrate the feasibility of the most critical process steps like continuous layer detachment, bonding to a carrier substrate, high-quality epitaxy, handling-free solar cell processing and module integration. As a deliverable, a mini module of higher than 18% efficiency shall be prepared.'

Introduzione (Teaser)

Scientists are increasing the throughput of solar cell production to provide an important increase in cost performance. Technology should foster more widespread market uptake.

Descrizione progetto (Article)

Photovoltaic (PV) modules that convert the Sun's energy into electricity are a promising sustainable alternative to the use of fossil fuels. Reducing their cost while providing adequate energy conversion efficiency will encourage even more widespread adoption of solar cell technology.

The so-called crystalline silicon (c-Si) thin-film lift-off approach promises to address both price and efficiency. Handling issues have reduced yield, thus increasing price relative to peak power (Watt-peak (Wp)) delivered. The EU-funded project 'Roll to module processed crystalline silicon thin-films for higher than 20 % efficient modules' (R2M-SI) promises to produce the thin films in a nearly handling-free process thus eliminating current limitations.

In the R2M-SI process, a very thin c-Si foil is lifted off the circumferential surface of a monocrystalline Si ingot in an electrochemical etch bath. The foil is attached to a substrate with high-temperature stability by means of suitable glue. After separation and attachment, the Si foil needs no more handling. It is subjected to in situ epitaxial thickening and application of an active solar layer (emitter) using chemical vapour deposition (CVD).

Researchers manufactured sintered Si substrates made from inexpensive Si powder and distributed them to partners. Free-standing and semi-attached porous Si layers were produced for attachment and epitaxy experiments. Several high-temperature glues were also identified and tested. Finally, scientists developed a continuous etching tool yielding successful preliminary etch results.

The next step was to develop processes for epitaxial deposition of active solar cell layers. All project deliverables and milestones were met, leading to development of the high-throughput continuous CVD tool (ConCVD).

Scientists are investigating solar cell and module processing combining experimental work with modelling and simulation. First process steps were tested and optimised and a prototype mini-module realised.

R2M-SI expects to deliver a process and manufacturing concept to produce highly efficient c-Si thin-film PV modules using the lift-off approach. Increasing PV cost performance by a process that consumes dramatically less Si will overcome one of the current barriers to more widespread market uptake of PV technology.