High-efficiency (19.2%) silicon thin-film solar cells with interdigitated emitter and base front-contacts

An interdigitated front grid structure for both the emitter and the base was realized. This contact design is suitable for thin-film solar cells on insulating substrates or insulating intermediate layers. Confirmed efficiencies of up to 19.2 % were achieved on a 46 µm thick epitaxial silicon layer which was grown on a Silicon On Insulator structure (SOI) with an implanted compact SiO2 intermediate layer. Various simulations were performed to study the influence of geometrical, optical and electrical parameters on the solar cell performance. The simulation resuts are in good agreement with the realized cells and enables now reliable predictions for SOI-cells with different cell parameters. It could be shown that the higher shadowing loss of the second front grid is widely compensated by the good reflection properties of the compact SiO2 intermediate layer. A cost-effective solar cell was prepared applying a Zone Melting Recrystallization (ZMR) step on CVD-grown, highly doped p+-Si layers which were deposited on SiC-encapsulated graphite substrates. Subsequently, the active Si-layer was grown in a RTCVD reactor with deposition rates of up to 10 µm/min. A newly developed completely dry-chemical solar cell process was applied to this system, substituting conventional wet etching steps by reactive ion etching (RIE). With this technology, conversion efficiencies of up to 11 % were obtained.