Effect of laser parameters and post-texturing treatments on the optical and electrical properties of laser textured c-Si wafers

Surface plays a crucial role in the performance of crystalline silicon (cSi) based solar cells as it affects both electrical and optical properties. To minimize reflection from the flat surface and thus improve light trapping, the cSi wafers must be textured. For mono-cSi cells, anisotropic alkaline etchants are commonly utilized to create pyramids on the surface. However, this method is not viable for multi-crystalline silicon (mc-Si) wafers due to the presence of different and random crystallographic orientations. In this work, we employed laser texturing, which is an isotropic texturing process, as an alternative texturing method for mc-Si wafers. This approach utilizes a laser process to create pits on the cSi surface. The laser's processing parameters were justified by performing a series of experiments. After texturing, physical (ultrasonic bath with deionized water) and chemical (in KOH with two different concentrations of 1 and 20%) cleanings with different durations were performed which were essential to remove laser-induced damages and other residues from the surface. In order to evaluate the optical response of the textured surfaces, weighted reflection values were measured and correlated with scanning electron microscopy (SEM) images of the textured features before and after post-texturing cleaning step. An impressive low weighted reflection of only 4.2% was measured from laser textured mc-Si with anti-reflection coating after optimizing the laser and post-texturing processes. Moreover, an implied open-circuit voltage (iVoc) of up to 692 mV was achieved by passivating the laser-textured surfaces by Al2O3.