Spray pyrolysis coating Al2O3:Cl/TiO2 bilayer for PERC

In this study we use low-cost spray pyrolysis method to produce a Al₂O₃:Cl/TiO₂ bilayer as rear passivation layer to replace the common known Al₂O₃/SiNx laminate in PERC structure silicon solar cells. The TiO₂ and TiO₂/Al₂O₃ mixed thin film acts a competent barrier from molten aluminum paste during the co-firing process and high refractive index of those thin films demonstrated excellent internal back reflectance (IBR). Very high negative fixed charge concentration is up to 5 × 10¹² cm^-2 in TiO₂ thin film being observed and the interface trap density (D_it) can be controlled via Ti/Al ratio and ultra-thin Al₂O₃:Cl interfacial layer to maintain good passivation ability and the lowest result of D_it is 8 × 10¹⁰ cm^-2eV^-1 with a 6nm Al₂O₃:Cl interfacial layer. Through the use of Al₂O₃:Cl interfacial layer, the carrier lifetime of bulk wafer increase from 60μs to 120μs. All of the results show that this concept is very promising for high efficiency silicon solar cell application.