Improving passivation properties using a nano-crystalline silicon oxide layer for high-efficiency TOPCon cells

Abstract

High conversion efficiency can achieve by superior surface passivation and material quality. In this study, a novel passivation contact structure based on nanocrystalline silicon oxide (nc-SiOx) films was investigated. Traditionally, poly silicon junctions in tunnel oxide passivated contact (TOPCon) solar cells possess exceptional junction characteristics, but current losses are noted due to their optical absorption if they are applied in solar cell devices. In this study, we replaced the poly-Si layer in TOPCon solar cells with nc-SiOx to enhance transparency. By employing the nc-SiOx layer, effective surface passivation, carrier selectivity, electrical properties and optical transmission can be used to improve, all are vitally important in devise operation. We optimized the deposited nc-SiOx layer on an ultra-thin (~1.5 nm) silicon dioxide (SiO2) tunnel oxide layer to improve recombination current density and carrier lifetime. The passivation characteristics were improved by varying the annealing temperature and thickness of the nc-SiOx layer. The 50 nm thick nc-SiOx layer was capable of yielding a high implied open-circuit voltage (i-Voc) of 739 mV and low contact resistivity (ρ) of 14.2 (mΩ/cm2) in addition to a low depleted recombination current density (Jo) of 1.1 fA/cm2 with a post-deposition annealing temperature up to 950 °C. Improved passivation characteristics are the result of a more prominent annealing temperature. Our proposed technique has immense potential for achieving higher efficiency for fabricating various structures of TOPCon solar cells. As per AFORST Het simulation results by using nc-SiOx for TOPCon structure, we got Voc of 761.5 mV, Jsc of 43.5 mA/cm2, FF of 83%, and η of 27.49%, respectively.