24.2% efficient POLO back junction solar cell with an AlOx/SiNy dielectric stack from an industrial-scale direct plasma-enhanced chemical vapor deposition system

Abstract

An aluminum oxide (AlO_x)/silicon nitride (SiN_y) dielectric stack was developed using an industrial plasma-enhanced chemical vapor deposition (PECVD) system with low-frequency (LF) plasma source for the surface passivation of undiffused textured p-type crystalline silicon. The median recombination current density is 4.3 fA cm⁻² as determined from photoconductance decay lifetime measurements and numerical device modeling. To the best of our knowledge, this is the first time to present a high-quality LF-PECVD AlO_x/SiN_y passivation stack on undiffused textured p-type crystalline silicon wafers, which are cleaned with industrial processes using HF, HCl, and O₃. The simulation agrees well with the measured effective carrier lifetime if the velocity parameters of 5.6 cm s⁻¹ for holes and 803 cm s⁻¹ for electrons are applied with a fixed negative charge density of −3 × 10¹² cm⁻². The process integration of developed AlO_x/SiN_y dielectric stack is successfully demonstrated by fabricating p-type back junction solar cells featuring a poly-Si-based passivating contact at the cell rear side. As the best cell efficiency, we achieve 24.2% with an open-circuit voltage of 725 mV on a M2-sized Ga-doped p-type Czochralski-grown Si wafer as independently confirmed by ISFH CalTeC.