Using 100 times less material than conventional technologies, active photovoltaic material of only two micrometers, the Institute of Microengineering EPFL obtained an efficiency of 10.7% for a solar cell thin film silicon beating the 1998 world record.

Laboratory (PV-Lab) of EPFL, part of its Institute of Microtechnology (IMT) in Neuchâtel, set a new efficiency world record for a silicon “microcrystalline” cell type. With a yield of 10.7%, the Swiss researchers exceeded 0.6% the previous record held since 1998 by the Japanese company Kaneka Corporation. This efficiency ‘remarkable’ was independently confirmed by the Fraunhofer Institute (ISE CalLab solar cells) of Freiburg (Germany).

This result may at first seem disappointing compared to the standards of the photovoltaic industry, which offers modules whose efficiency ranges between 15 and 20%. Conventional photovoltaic technology is based however on wafers of crystalline silicon having a thickness of about 180 micrometers.

Technology developed PV-Lab puts to reach 10.7% efficiency at 1.8 micron silicon only 100 times less material than conventional technologies. This process allows saving raw materials and provides short time “energy payback” the energy required for the production of modules is recovered in less than a year in sunny regions.

These benefits are reflected in producer prices as low as 40 modules CHF/m2, reaching the level of prices terracotta tiles used for roofing.

“An understanding has been gained in recent years in both the cell design, the quality of materials used and effective in trapping light, which, combined with the optimization of manufacturing processes, led to this record efficiency,” said Simon Hänni, PhD student at IMT. Importantly, the methods used can be easily transferred to the module.

Combination of amorphous and crystalline silicon

Progress is of paramount importance to increase the efficiency of photovoltaic thin film: a junction microcrystalline silicon is always used in combination with amorphous silicon to form multi-junction devices, which cover the solar spectrum optimally and to obtain higher yields.

The efficiency obtained today by the team of Matthew and Fanny Meillaud Despeisse clearly indicates the potential of cells in thin silicon layers can be extended to conversion efficiencies of 13.5% with a minimum use of raw materials. These are additionally abundant (and therefore low-cost) and non-toxic, module silicon thin film containing only two glasses and a few microns of zinc and silicon, thus allowing easy recycling.

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