**2. Process flow and current status**

Conventional silicon solar cell process and its current status in PV industry are discussed in detail. Subsequently, the process steps of advanced process techniques such as Ni/Cu plating-based silicon solar cell, PERC, and IBC are also discussed.

## **2.1 Conventional Si solar cell**

Currently, most of the PV industries use boron-doped p-type wafers as the starting material for c-Si solar cell fabrication. The schematic diagram of conventional fabrication process is shown in **Figure 1**. As reported in [2, 21], every processing step contributes to losses in conventional screen printing solar cell. Screen printing metallization is cost-competitive and robust technology used in production. Screen printing technology has attracted considerable attention due to significant improvement in printing medium and simplicity of the process. Also, this technology increases the throughput and decreases the production cost. For metallization, several alternatives to screen printing are available to improve cell efficiency [22, 23]. However, the existing screen printing technology is the matured and cost effective technology [24, 25] compared to recently developed technologies such as PERC, IBC, and HIT. Hence, around 85% of Si solar cells are manufactured using screen printing of thick film pastes. In a typical solar cell process, screen printing has the potential to improve efficiency and lower the cost, since metallization pastes are continuously evolving and new generation of pastes are available.

In addition to the new generation pastes, the right choice of front grid design and screen pattern results in better efficiency with reduced cost. The new generation paste provided a better aspect ratio (the ratio of line height to line width). The improvement in the aspect ratio improves the current carrying capacity of the contacts, as the shadow loss is decreased as well as the series resistance also decreases. In addition to the paste rheology, enhancement of the aspect ratio relies on choosing the right screen parameters such as mesh count, wire dimension, and emulsion thickness. Along with the paste material, optimized screen parameters are also the important factors for making the front contact with high aspect ratio and reduced shadow loss, which are desired for getting high efficiency solar cells. The silicon solar cell researchers or industries have achieved a maximum efficiency of 19% on multicrystalline silicon and around 20% on mono crystalline silicon-based solar cells by using the conventional process as shown in **Figure 1** and are still working to enhance the efficiency using advanced materials.

Screen printing-based metallization technology occupies the significant role in solar cell manufacturing due to high throughput in cell production with better efficiencies. Though it is a mature technology, the finger aspects of the cells were limited by screen specifications and paste rheology.

**Figure 1.** *Si solar cell process flow.*
