2. Technology details
Fig. 1a and b shows a simplified drawing of the MWT structure studied in this paper. The emitter contact (red) reaches the back side of the cell by a silver-metallized via. In the MWT architecture, the front side contacts reach the cell backside through a series of laser-drilled holes (vias) filled by silver paste. In this way, the front side busbars are removed and all the interconnections of the cells are made on the backside, reducing the front side shadowing and ultimately increasing the cell efficiency. Typically an MWT cell contains 9–200 vias, with diameter ranging from 50 mm to 200mm
[11]; in this work we focused on a structure comprising 16 vias of 200 mm, arranged in a square matrix on the cell [12].
The laser drilling step can be performed in different stages of the cell production flow, resulting in different emitter structures; in particular, depending on the vias being drilled before phos-phorus diffusion or afterwards, we can respectively obtain the emitter layer in the vias walls or not (Fig. 1a and b). This work studies two different emitter structures: in the first one, the emitter is created by ion implantation and the drilling step is