Novel low-cost alkaline texturing process for diamond-wire-sawn industrial monocrystalline silicon wafers

Abstract

Diamond-wire-sawing (DWS) processes have been developed in recent years to overcome the problems of silicon (Si) waste and low throughput of the conventional multi-wire-slurry-sawing (MWSS) process for cutting Si ingots into wafers. However, DWS is not adopted extensively by PV industry as standard alkaline texturing is not directly applicable to these wafers to generate regular pyramidal structure. In the present work we are reporting a novel low-cost alkaline texturing process for industrial DWS monocrystalline silicon (c-Si) wafers. Our process has three novelties; firstly, it uses a low-cost saw damage removal (SDR) process with a new recipe of potassium hydroxide (KOH), sodium hypochlorite solution at 80 °C for slow Si etching. This process also successfully removes the amorphous Si layer normally present on the as-cut DWC Si wafer surface. Secondly, no initial cleaning process is required before our SDR process. Finally, a high throughput KOH/isopropyl alcohol/potassium silicate texturing process was applied successfully for pyramid formation on the DWS c-Si wafers. Small (~2–4 µm in height) and uniform pyramidal structure with reduced surface reflectance is confirmed by scanning electron microscope, Zeta 3D measurement and UV–Vis spectroscopy studies. Further, photoluminescence (PL) imaging of lifetime samples prepared with the present texturisation process, confirmed the uniformity of surface passivation, a prerequisite for solar cell fabrication. Screen-printed solar cells were fabricated in NCPRE cell fabrication laboratory. For our 6 in. pseudo-square CZ p-type c-Si wafers cell efficiencies up to 18.5% were achieved with the new texturing process. This high throughput novel texturing process thus can easily be integrated into the standard industrial process.