Self-aligned local contact opening and n+ diffusion by single-step laser doping 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 POx/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 POx 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 POx/Al2O3 passivation stacks having J0 of 2.5 fA cm−2. The combination of outstanding passivation of uncontacted n-type regions offered by POx/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.