Vapor-textured EFG Silicon Photovoltaic Cells

Abstract

Solar cell fabrication using edge-defined film-fed growth Si (EFG-Si) is an important process because of its cost effectiveness compared to fabrication using crystalline Si (c-Si). In our work, a new technique called vapor texturing was used to achieve effective texturing of EFG-Si. Texturing using an acidic solution, HF:HNO(3):CH(3)COOH:DI water in the volume ratio 8:21:10:8, was performed on p-type EFG-Si wafers with resistivity 0.5 - 2 Omega.cm and a thickness of 300 mu m for 3 min. An etching depth of about 4 mu m was achieved on both sides of the EFG-Si wafers. The acid treated EFG-Si wafers were textured again using vapor mixture of HF and HNO(3) in the volume ratio 7:3 with 8 g of Si. The average surface reflectance of EFG-Si wafers subjected to one-step acid texturing and to two-step acid and vapor texturing were found to be 22.30% and 5.04%, respectively. The sheet resistance of EFG-Si wafers subjected to one-step and two-step acid texturing were 85 Omega/sq and 50 Omega/sq, respectively, after phosphorous doping. After an effective drive-in process accompanied by surface passivation had been done, a sheet resistance of about 45 Omega/sq was achieved for wafers subjected to the two different texturing schemes. The effective minority carrier lifetime after vapor texturing and SiNx:Ii deposition was about 19.54 mu s. SEM analysis of the surface morphology showed clear changes after each process.