Large area p-type PERL cells featuring local p+ BSF formed by laser processing of ALD Al2O3 layers

• Incorporation via laser processing of Al present in Al2O3 into Si to form local BSF.
• Deep BSF (≥2.5 μm) combined with high effective lifetimes.
• Same ALD Al2O3 as passivation and doping layer.
• Improved efficiency with respect to PERC process based on fired rear contacts.
• Efficiency of 20.7% on 6-in. p-type Cz–Si with simple and cost-effective process.

In this work we present large area p-type PERL solar cells featuring local p+ Back-Surface-Field (BSF) obtained by pico-second (ps) laser processing of thin ALD Al2O3 layers capped either by PECVD SiNx or PECVD SiOx. In this specific approach, the laser processing is performed through the rear passivation stack, whereby the laser simultaneously patterns the dielectrics for the subsequent Al–Si contact formation, whilst incorporating the Al atoms from the Al2O3 film into the underlying Si bulk. With this technique, we register substantial dopant incorporation for 10 nm of ALD Al2O3, without using additional doping sources. When this process is coupled to a front metallization scheme based on Cu plating, p-PERL cells can be fabricated adopting only low temperature process steps, which avoids thermal stability issues related to the Al2O3 layer, such as crystallization and blistering, and improves the properties of the rear reflector by avoiding Al–Si alloying. Efficiencies up to 20.7% are reported on 6-in. Cz–Si solar cells featuring local p+ BSF formed by laser doping through a rear stack composed of 10 nm ALD Al2O3 and 120 nm PECVD SiNx.