Evaluation of dominant loss mechanisms of PERC cells for optimization of rear passivating stacks

In this paper a comprehensive theoretical analysis has been carried out for Passivated Emitter Rear Contact (PERC) solar cells with the help of numerical modeling using Sentaurus TCAD simulation software. For the rear passivation we have explored various dielectric layers, such as, Aluminium Oxide (Al2O3), Silicon Oxide (SiO2), Hafnium Oxide (HfO2) and Aluminium Nitride (AlN) along with the Silicon Nitride (SiNx) capping layer. Optical generation near the rear side the passivating stacks was analyzed. Recombination current densities were also evaluated for assorted defects with various concentration, hole and electron capture cross sections and position of quasi Fermi level for surface passivation. Thicknesses of the passivating and capping layers were optimized with respect to optical and electrical losses. Field effect passivation (FEP) property of the rear passivating stacks was also investigated. For simulated textured Al-BSF solar cell on silicon wafer of bulk lifetime 250µs, an efficiency of 19.5% was obtained. This solar cell has been used here for reference. We have achieved efficiency of 22.6% for PERC solar cells of rear contact area of 8% on similar type of wafer. It was noticed from few articles that industrial PERC solar cells were fabricated using rear metal contact less than 10% which is well validating our study. It was also perceived that employing Passivated Emitter Rear Totally Diffused (PERT) structure with optimized design parameters further improved the efficiency to ∼ 24%.