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MICROMORPH ( MICROCRYSTALLINE / AMORPHOUS SILICON ) TANDEM SOLAR CELLS : Status Report and Future Perspectives

Hydrogenated microcrystalline silicon (μc-Si:H) as deposited by PECVD at low temperatures (around 200°C) can be used to fabricate stable pin-type solar cells with conversion efficiencies over 8 %. The variety of growth forms and microstructural patterns observed for different deposition conditions is described; the requirements to be met by layers for use in μc-Si:H solar cells are listed. A particularly advantageous configuration is given by the microcrystalline / amorphous (or “micromorph”) tandem cell, where stabilized laboratory efficiencies between 11 and 12% are now reached. Stabilized module efficiencies are at present around 9 %. Future scope for performance improvement lies mainly in increasing the short-circuit current further. The use of light-trapping is at present the best way to achieve this. Thereby, one of the possibilities (illustrated in the paper) is to use ZnO, deposited by LP-CVD, as a rough, light-scattering TCO layer.