Optical modeling and characterization of bifacial SiNx/AlOx dielectric layers for surface passivation and antireflection in PERC

Abstract

In this research, we analyzed the impact that the optical characteristics of dielectric surface passivation and antireflection coating schemes have on the performance of passivated emitter and rear cell (PERC) silicon solar cells. We employed wafer ray tracer (WRT) and automate for simulation of heterostructure (AFORS-HET) simulations, as well as experimental characterization of fabricated thin film coatings. We investigated three distinct front surface morphologies: planar surface, upright pyramids, and inverted pyramids. Using WRT, we calculated the photogeneration current densities (J_G) for PERC devices with three schemes: (i) SiN_x/AlO_x as antireflection coating and passivation stacks on both the front and rear sides, (ii) SiN_x antireflection coating on the front side and AlO_x passivation layer on the rear side, and (iii) SiN_x/AlO_x as antireflection coating and passivation stacks on the front side with an AlO_x passivation layer on the rear side. Following simulation with optimal J_G, two schemes are experimentally evaluated: PECVD SiN_x (70 nm) and atomic layer deposition (ALD) AlO_x (15 and 25 nm). We confirmed the growth effects and optical properties using X-ray diffraction, Raman spectroscopy, effective lifetime, and refractive index measurements. The most favorable electrical properties were obtained with SiN_x (70 nm, front) and AlO_x (25 nm, front and rear), where the AlO_x can be deposited via ALD bifacially on a single step, minimizing processing while maintaining passivation performance. Finally, we used AFORS-HET to simulate the maximum performance of PERC bearing such films. The results showed a V_oc = 0.688 V, J_sc = 41.42 mA/cm², FF = 84%, and packing conversion efficiency (PCE) = 24.12% as the optimal solar cell performance values.