**4.3 Wet-chemistry-based edge isolation**

The emitter region in a solar cell is fabricated by a high temperature diffusion process (to be discussed in sections ahead). During the diffusion process, phosphor silicate glass (PSG) is deposited on the wafer which should be removed before deposition of the ARC layer. As depicted in **Figure 10**, after the diffusion step, the n-type region is also present on the edges and the rear-side of the wafer. The n-type layer on edges and the rear-side will short-circuit the emitter with the base substrate and hence it is important to etch these regions and isolate the emitter on the FS from the base substrate as depicted in **Figure 10(c)**.

The edge isolation process can be performed in an inline manner similar to the texturing process discussed in the previous section. The exception in this case is that the chemical should etch only the rear-side and edges without interacting with the FS. A representative image of the edge isolation process is shown in **Figure 11**. It is important to note that the rollers are present only on the bottom-side to avoid any contact of the etching solution with the front-side. The subsequent steps after the RS etching are similar to those in the inline texturing machine.

**Figure 10.**

*Processing of silicon wafer after diffusion and edge isolation (a) Textured silicon wafer, (b) Diffused silicon wafer, (c) Diffused silicon wafer after edge-isolation.*

#### **Figure 11.**

*Representative image of solar cell in an inline edge-isolation bath.*
