Efficient and cost-effective solar energy conversion
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.
