*3.1.2. Light-induced deposition*

Light source along with an electroless deposition process were used to deposit a Ni barrier layer. The phenomenon of a chemical reaction taking place is the same (catalytic oxidationreduction) as described in the previous section. However, the light source provided here helps in adjusting the electrochemical potential of the front are rear of the cell and enhances the plating rates [42]. The electron migration at the surface is controlled by the photo-voltage generated from the np-junction and the electronegativity of the substrates. Moreover, higher plating rates can be achieved as these photo-generated electrons enhance the reduction of the Ni2+ions on the silicon surface [15]. The increase in the plating rates due to light inclusion relives in the form of operating the bath at lower temperatures. Although a uniform Ni layer at higher plating rates can be deposited, the process of light-induced electroless plating involves complexity related to the process's characterization. Furthermore, the light-induced current in the LIP process helps to transport electrons only to the n-type surface, which limits the technique in metallizing n-type surfaces [43]. The light-induced nickel plating (LINP) process was also investigated by Yu-Han et al., and uniform Ni surfaces of high intrinsic quality were reported [44].

### *3.1.3. Laser-assisted deposition*

Laser-assisted deposition has also been used to employ the Ni deposition process on a silicon surface. The process is considered to be feasible for industrial applications, as the anti-reflection coating (ARC) layer can be ablated along with the Ni deposition. This can reduce the number of steps involved in cell processing and can help the development of solar cells with mass production on the industrial scale.

Here, an electrolyte solution is used where a cell composed of an np-junction is immersed and a laser beam is applied to pattern the grid at the wafer surface. The application of the laser beam increases the temperature in the solution and at the wafer surface [20]. The ARC is ablated due to the heat generated at the laser-exposed surface and increased temperatures in the electrolyte solution decompose the Ni particles. Furthermore, the light induced in the cell generates an electron-hole pair, the generated electrons support Ni deposition at the sample surface. The use of water containing Ni salts is considered to be useful for depositing the Ni layer on the silicon surface uniformly. There has been some progress reported regarding laser chemical Ni deposition by various research institutes [45-50], although the process still needs to matured. Laser chemical metal deposition (LCMD) is a solution for implementation on the industrial scale since ARC ablation along with Ni deposition can be performed at the same time. The LCMD process was successfully implemented at Fraunhofer ISE to form Ni-based Cu metallization with 17.9% efficient cells on CZ substrates [51]. Röder et al. also reported a laser-based method to deposit a Ni layer with thinner finger widths (< 30 μm) with a low temperature process known as 'laser transfer contact' (LTC) [52].
