Laser contacts from POx/Al2O3 passivation stacks

Abstract

Laser doping is a promising route to realise industrially compatible processing of local contacts for high-efficiency solar cells, especially when the same film acts as both dopant source and passivation layer. In this work we demonstrate simultaneous local contact opening and n+ laser doping of silicon from positively charged PO_x/Al₂O₃ thin-film stacks, which also provide outstanding passivation of n-type silicon surfaces. Local n+ doped regions with sheet resistance ranging from 35 to ~540 Ω/□ are formed using single nanosecond laser pulses with varying fluence. ECV profiling shows net n-type doping in all cases, confirmed by SIMS profiling to be due to phosphorus from the PO_x layer. J₀ of metallised laser-doped regions is consistent with values achieved for state-of-the-art furnace diffusions with similar sheet resistance, confirming that laser-induced recombination-active defects are avoided. A minimum J₀ of 540 fA cm⁻² is obtained for metallised laser-doped regions formed from PO_x/Al₂O₃ passivation stacks having J₀ of 2.5 fA cm⁻². The combination of outstanding passivation of uncontacted n-type regions offered by PO_x/Al₂O₃, with self-aligned formation of locally-diffused contact openings via single-step laser processing, opens up exciting possibilities for simplified fabrication of high-efficiency cell structures.