Formation of emitter by boron spin-on doping from SiO2 nanosphere and properties of the related n-PERT solar cells

Abstract In this paper, spin-on doping (SOD) process using commercial boron dopant source was applied to form front p-type emitter on n-type mono-crystalline CZ substrate. Results showed that the thickness of boron rich layer (BRL) decreased from 180 nm to 20 nm with SiO2 nanosphere assisted SOD and the BRL can be removed entirely by further in-situ oxidation. Furthermore, the hole concentration of the emitter reduced from 5.5 × 1019 cm3 to 2.8 × 1019 cm3 by integrating these two processes. In a symmetric sample without BRL, a very low emitter saturation current density of 32 fA/cm2 with implied-Voc over 700 mV was obtained. The minority carrier lifetime got improved more than 30% after diffusion. Finally, n-PERT solar cell with a conversion efficiency of 20.26% was achieved using optimized boron emitter, showing an enhanced conversion efficiency of 0.54%.