UV laser direct texturing for high efficiency multicrystalline silicon solar cell

Surface texturing is a technique used to increase light-trapping by forming certain structures on surface of a photovoltaic cell. We performed direct surface texturing using a 355 nm UV laser to create V-shaped grooves on p-type, boron-doped multicrystalline silicon wafer of 200 μm thickness. In addition, a 1064 nm fiber laser was used to fabricate U-shaped grooves; this was done to determine the effect of light-trapping according to the shape of the structure. The samples were processed by 25% NaOH and acid solutions to remove slag after the direct texturing and isotropic etching. The reflectance and minority carrier lifetimes were measured to analyze the effects of the V-shaped groove and U-shaped groove. The V-shaped groove sample without the etching process showed 8.6% reflectance, while the sample etched for 4 min with NaOH and 4.5 min with isotropic acid after the laser texturing showed 13.2% reflectance. The minority carrier lifetime of the UV laser, V-shaped groove sample increased from 2.6 μs to 20.6 μs while that of the fiber laser, U-shaped groove sample increased from 2.3 μs to 5.9 μs. Etching was essential to remove slag and damages from the laser processes since these defects can induce inefficient electrical performance, as in long carrier lifetime. However, excessive etching flattens the surface and results in reduced effectiveness of light trapping. Consequently, the densely-packed V-shaped textures were more effective for capturing photons than the U-shaped texture.