Magnesium oxide–based passivation and anti-reflection stack for back-contact silicon solar cells

Back-contact (BC) crystalline silicon (c-Si) solar cells require high-quality front-side passivation together with effective anti-reflection. In this work, we report a silicon oxide/magnesium oxide/aluminum oxide (SiO2/MgOx/Al2O3) passivation and anti-reflection stack, in which the passivation performance of atomic-layer-deposited (ALD) MgOx is significantly enhanced by incorporating an ultrathin SiO2 interlayer and an ALD Al2O3 capping layer. The effects of the SiO2 formation process, annealing conditions, and the thicknesses of MgOx and Al2O3 on the passivation properties of the SiO2/MgOx/Al2O3 stack are systematically investigated. As a result, excellent surface passivation is achieved on planar n-type c-Si surfaces, yielding an implied open-circuit voltage (iVoc) of up to 735 mV and a recombination current density (J0) as low as 2.2 fA cm−2. This improvement is attributed to enhanced chemical passivation induced by increased hydrogen incorporation and suppressed hydrogen effusion enabled by the Al2O3 capping layer. In addition, positive fixed charges in the n-Si/SiO2/MgOx/Al2O3 structure further contribute to the passivation through a field-effect mechanism. The demonstrated SiO2/MgOx/Al2O3 stack therefore represents a promising front-side dielectric solution for high-efficiency BC c-Si solar cells.