**2.2 Sand blasting process**

40 Solar Cells – Thin-Film Technologies

techniques including, electro-polishing, sandblasting, photolithography, lift-off and wetchemical etching were used to create periodically textured structures on the different types of stainless steel substrates. The relationships between the surface morphology of textured

In this study, electrochemical processing was used to achieve sub-micro texturing stainless

OH-→O2↑+H2 (Parasitic reaction) (2)

2H+→H2↑ (3)

The clamp was used to hold the anode and cathode plates. The anode and cathode plates were separated by Teflon with thickness of 1 cm. Fig. 2 shows the optical microscopy (OM) images of 304 SS substrate with and without EP process. The average surface roughness (Ra) of 304 SS substrate increased from 0.045 μm to 0.197 μm after the EP process with current

The electro-polishing system is shown in Fig. 1. The important parameters are as follows:

→Fe(OH)2 or Fe(OH)3 (1)

陽極 陰極

Anode Cathode

Na2SO4電解液

Na2SO4 electrolyte

stainless steel substrate and optical properties will be carefully discussed.

steel substrate base on the fundamental electrochemical reaction items as (1)-(3).

**2. Surface treatment of texturing stainless steel substrate** 

1. Substrate clean by acid-washing in H2O2:H2SO4=1:3 solution. 2. Electrolyte solution (Na2SO4) with concentration of 60-100 (g/L). 3. Current density in electro-polishing (EP) process is 0.1-1.0 (A/cm2).

**2.1 Electro-polishing process** 

Fe2++2(OH)-

Anode chemical reaction:

Cathode chemical reaction:

density of 1A/cm2 in 10 min.

Anode clamp area

Fig. 1. Experimental set-up of the EP process.

Reaction area

The glass sand (#320) was used to form randomly textured surface with cave size of several μm to tens μm on the surface of stainless steel substrate. The average surface roughness (Ra) of 304 SS substrate increased from 0.277 μm to 6.535 μm after the sand blasting process. The OM images of raw 304 SS substrate and with sand blasting process were shown in Fig. 3.

Fig. 2. The OM images (x2000) of (a) raw 304 SS substrate surface and (b) 304 SS substrate surface with EP process.

Fig. 3. The OM images (x400) of (a) raw 304 SS substrate surface and (b) 304 SS substrate surface with sand blasting process.
