Spray pyrolysis coating Al2O3:Cl/TiO2 bilayer for PERC

In this study we use low-cost spray pyrolysis method to produce a Al
2
O
3
:Cl/TiO
2
bilayer as rear passivation layer to replace the common known Al
2
O
3
/SiNx laminate in PERC structure silicon solar cells. The TiO
2
and TiO
2
/Al
2
O
3
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 × 10
¹²
cm
⁻²
in TiO
2
thin film being observed and the interface trap density (D
it
) can be controlled via Ti/Al ratio and ultra-thin Al
2
O
3
:Cl interfacial layer to maintain good passivation ability and the lowest result of D
it
is 8 × 10
¹⁰
cm
⁻²
eV
⁻¹
with a 6nm Al
2
O
3
:Cl interfacial layer. Through the use of Al
2
O
3
: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.