Shadow-epitaxy for flexible crystalline thin-film silicon solar cell design

Crystalline silicon thin-film solar modules require a cost-effective means for the fabrication of an integrated series connection. We introduce selective epitaxy by ion-assisted deposition through shadow masks for the integrated series connection of ultrathin monocrystalline and textured Si solar cells. The series connection is made in situ during Si-film deposition thus avoiding any trench etching. The open-circuit voltage of an experimental mini-module consisting of six cells is six times as large as the open-circuit voltage of a single cell. Epitaxy through shadow masks also permits the in situ realization of parallel multi-junction solar cells. The experimental quantum efficiency analysis of a parallel multi-junction device with three junctions reveals an enhanced carrier collection. The apparent effective diffusion length of the multi-junction cell is three times larger than that for a conventional single-junction device.