*3.4.1. Wet etching*

The Cu electroplating is mostly done by the approach implementing LIP arrangements as shown in Fig. 5. The LIP process works on the same principle as the conventional electroplating process; however, the inclusion of a light source enables the utilization of the photo-generation property of the solar cell. This process, developed at Fraunhofer ISE, includes the immersion of a patterned cell into the electrolyte plating with the light source arrangements. A protective potential is applied at the sample in order to make the rear-side of the cell more cathodic, which helps in minimizing the corrosion of the aluminium back-electrode. Furthermore, the plating can also be done relatively uniformly, as this potential operates the cell closer to its short-circuit conditions [43]. As to having a uniform voltage distribution across the grid pattern, the LIP process also provides stable baths with no reducing agents. LIP is an encouraging method, particularly for the solar cell metallization since it helps to deposit metal with higher aspect

**Figure 5.** Schematic arrangements of Cu-based light-induced electroplating systems.

The conventional Ag metal contacts are usually formed by screen-printing and firing the Ag pastes through SiNx passivation layers. However, Ni/Cu-based metallization requires a separate step to open the ARC/passivation layer in order to form the contact grid. A simple example could be a mask and etch sequence [42]. Under this method, the passivated front surface of the cell is patterned with a photolithography process and the unprotected passivated layer is etched away using wet etching. Later on, the photoresist (PR) material is stripped away in an organic solvent solution (the process sequence is described in Fig. 6). For patterning the front contact grids, various approaches have been adopted. These approaches can be catego‐ rized as wet etching, direct etching, mechanical scribing and laser-assisted etching. All these

ratios and higher deposition rates.

286 Solar Cells - New Approaches and Reviews

**3.4. Anti-reflection coating (ARC) patterning**

etching methods will be discussed in this section of the chapter.

The process of wet etching involves the front-electrode grid opening in the passivation layers through a wet chemical solution (e.g., hydrofluoric acid). An example of a mask and etch sequence using a photolithography process has already been discussed. The photolithography process has the ability to open finger lines with lower widths (reduced shading losses). Although the photolithography-based grid patterning has shown great results in the form of higher efficiencies, nonetheless the process complexity limits its implementation on the industrial scale. Other methods, such as the use of etch resists deposited by either screen printing or ink-jet printing followed by ARC etching by wet chemical treatment, have also been employed [57, 58]. The ink-jet by aerosol jet printing has also been used to etch away the contact grids by non-contact writing for front metallization [23, 57]. The wet etching methods involve some cleaning steps, which restrict their implementation on the industrial scale.
