Electrical and optical characterization of SiOxNy and SiO2 dielectric layers and rear surface passivation by using SiO2/SiOxNy stack layers with screen printed local Al-BSF for c-Si solar cells

In c-Si solar cells, surface recombination velocity increases as the wafer thickness decreases due to an increase in surface to volume ratio. For high efficiency, in addition to low surface recombination velocity at the rear side, a high internal reflection from the rear surface is also required. The SiOxNy film with low absorbance can act as rear surface reflector. In this study, industrially feasible SiO2/SiOxNy stack for rear surface passivation and screen printed local aluminium back surface field were used in the cell structure. A 3 nm thick oxide layer has resulted in low fixed oxide charge density of 1.58 × 1011 cm−2 without parasitic shunting. The oxide layer capped with SiOxNy layer led to surface recombination velocity of 155 cm/s after firing. Using single layer (SiO2) rear passivation, an efficiency of 18.13% has been obtained with Voc of 625 mV, Jsc of 36.4 mA/cm2 and fill factor of 78.7%. By using double layer (SiO2/SiOxNy stack) passivation at the rear side, an efficiency of 18.59% has been achieved with Voc of 632 mV, Jsc of 37.6 mA/cm2, and fill factor of 78.3%. An improved cell performance was obtained with SiO2/SiOxNy rear stack passivation and local BSF.