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 (AlOx)/silicon nitride (SiNy) 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 AlOx/SiNy 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 AlOx/SiNy 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.