Surface passivation by silicon nitride in Laser Grooved Buried Contact (LGBC) silicon solar cells

Surface passivation is a crucial parameter in crystalline silicon solar cells. A layer of silicon dioxide (SiO2) and a silicon nitride (SiNx) has been grown on Laser Grooved Buried Contact (LGBC) cells at different temperatures and annealing times by the new High Target Utilisation Sputtering (HiTUS) to improve surface passivation. To evaluate the performance of the SiO2 and SiNx layer a Cary 5000 spectrophotometer was used to measure the reflectance of the silicon wafer as a function of the wavelength. Wafer mapping was performed using the Laser Beam Induced Current (LBIC) technique to measure the diffusion length and the lifetime of the minority carriers. Photoconductive Quasi Steady State (QSS) measurements by a WCT-100 were performed after each thermal process to measure the effective lifetime of p-type Cz–Si wafer Boron doped 〈100〉〈100〉 as a function of the excess carrier concentration. Results have demonstrated that SiNx increases the diffusion length and the effective lifetime improving surface passivation; thus decreasing the number of defects at the surface.