Excellent surface passivation of heavily doped p+ silicon by low-temperature plasma-deposited SiOx/SiNy dielectric stacks with optimised antireflective performance for solar cell application

Abstract

The passivation of p+ Si surfaces is challenging due to the fact that most passivation films have an intrinsically high positive fixed charge. In this work we show experimentally that low-temperature plasma-enhanced chemical vapor deposited SiOx/SiNy stacks with a low positive fixed charge density (+1011cm−2) and very low interface defect density (~3×1010eV−1cm−2) as measured by contactless corona-voltage measurements can effectively passivate p+ surfaces resulting in emitter saturation current density (J0e) values of 25 and 45fA/cm2 on planar and textured 75Ω/sq p+ silicon after industrial firing with a set-temperature of ~800°C, respectively. Based on contactless corona-voltage measurements and advanced device simulations, we explain the mechanism of surface passivation by PECVD SiOx/SiNy dielectric stack to be completely dominated by chemical passivation rather than field-effect passivation. Furthermore, from advanced device simulations we illustrate the role of fixed charge in surface passivation and in the extraction of fundamental surface recombination velocity parameter for p+ silicon surfaces. The fundamental surface recombination velocity parameter for electrons is determined to be about 400cm/s at these c-Si/SiOx interfaces. With excellent optical and passivation properties, SiOx/SiNy dielectric stacks are suitable for high-efficiency and cost-effective industrial n-type silicon wafer solar cells.