Dry processing of mc-silicon thin-film solar cells on foreign substrates leading to 11% efficiency

A dry-chemical solar cell process has been developed by substituting conventional wet etching steps by reactive ion etching. The performance of mc-Si solar cells that have been made by this new technology is comparable to that of conventionally processed cells. Thin-film solar cells have been prepared by applying zone melting recrystallisation of CVD-grown, highly doped p⁺-Si layers, that were used as seeding layers for the growth of the active Si-layers. Graphite with two kinds of encapsulation have been used as a foreign substrate for the silicon deposition: (a) covered with conducting SiC, the graphite acts as base contact of the cells; and (b) graphite encapsulated with insulating SiC- and SiO₂/SiN/SiO₂-layers (ONO) leads to solar cells on insulating foreign substrates, with front side base contact. The graphite/SiC/Si layer system was developed by ASE; ONO deposition and recrystallisation were realised at Fraunhofer ISE. Applying the authors´ dry solar cell technology, conversion efficiencies up to 11% were achieved