Epitaxy wrap-through rear contact solar cell fabrication and results

The Epitaxy Wrap-Through (EpiWT) cell is a rear-contacted c-Si epitaxial thin-film solar cell. It is a cross between the Epitaxial Wafer-Equivalent and Emitter Wrap-Through (EWT) solar cells. An epitaxy-throughholes process has been developed to deposit the active layers onto the low-grade silicon substrate, whereby a beneficial geometrical structure is produced. The rear-side structuring is achieved with screen-printing and other industrially feasible processes. The characteristics of the EpiWT cell, in comparison to the EWT cell, require a small rear-side emitter area fraction and the incorporation of an isolation layer. The first ever EpiWT solar cells have been fabricated and a cell efficiency of 10.3% has been achieved (with the busbars outside the 4 cm2 illuminated aperture area). The cell performance is still limited by processing difficulties, so the structure has yet to be optimised. The dominant loss mechanisms and the effect of the isolation layer are analysed.