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Abstract: To answer the challenge of less expensive renewable electricity, the photovoltaics community is focusing on producing thinner silicon solar cells. A few years ago, in the field of silicon-on-nothing structures, micron-thick monocrystalline layers suspended over their parent wafer were produced by high-temperature annealing of specific arrays of macropores. Those macropores reorganise into one single void and leave a thin overlayer on top. Since this method may be an inexpensive way of fabricating high-quality silicon films, this paper investigates its potential for photovoltaic applications. In particular, we investigated if large surfaces can be produced and transferred to foreign substrates with this method. We fabricated basic solar cells, without rear-surface passivation, on 5cm×5cm-large and 1-μm-thick films transferred to glass, that showed energy-conversion efficiencies up to 2.6%. These cells demonstrate the feasibility of the presented concept as a layer-transfer process for solar-cell application. After formation by annealing, the film is only barely attached to its parent wafer, but can still safely be handled provided that any abrupt gas flow or pumping to vacuum is avoided. After transfer and permanent bonding, the sample can be handled as any bulk wafer. [Copyright &y& Elsevier]

Abstract: Thin layers of silicon for solar cells can be lifted-off from wafers by taking advantage of the property of macropores to reorganise at high temperature and, in specific conditions, to form a high-quality layer on top of an empty space. Those conditions need to be identified and this work focuses in particular on the annealing ambient composition. Its influence was investigated by scanning and transmission electron microscopy and by Fourier-transform infrared spectroscopy. Apart from hydrogen, which has been used in previous studies, argon was found to be also compatible with the reorganisation. This result points out that the presence of oxygen impurities may not be as deleterious as expected, but that those impurities complicate the set of reactions taking place during the high-temperature process. [Copyright &y& Elsevier]

A promising cost-effective way of converting sun light into electricity could be a solar cell realized in a thin monocrystalline silicon film, due to its potential to achieve cell efficiencies of more than 20% in a 20 μm thick film. A porous silicon layer transfer technique provides an opportunity to get monocrystalline films on low-cost substrates such as glass. This paper reviews various processes, which are being developed for the layer transfer using porous silicon as a sacrificial layer while reusing of starting silicon substrate. The four basic steps—porous silicon formation, active layer deposition, layer separation and transfer, and device fabrication—have been identified in layer transfer process. The processes have been categorized and compared on the basis of the sequence of steps used in individual processes. [Copyright &y& Elsevier]

Thin film monocrystalline silicon solar cells based on porous silicon (PS) layer transfer processes could be cost-effective because of their lower consumption of material use and the potential for high efficiency. The process is based on our ability to separate thin porous films (p+) of desired thickness and area from Si substrate. Crystallinity of these porous films is studied with XRD for their suitability for Si epitaxy. AFM is employed to study the Si substrate surface roughness after one or more porous film separations. The roughness stabilizes after four film separations. Annealing of the porous films at temperatures above 1050 °C results in a closed surface, suitable for Si epitaxy. XRD analysis of epitaxially deposited Si layer on annealed PS film revealed its high mono-crystalline quality. A FMS solar cell of 12% efficiency has been realized in an 18 μm thin epitaxial layer. [Copyright &y& Elsevier]