Atomic-layer-deposited BOx/Al2O3 stack for crystalline silicon surface passivation

Abstract

Surface passivation is a crucial factor in improving the efficiency of c-Si solar cells. In this work, we develop a boron oxide/aluminum oxide stack (BOx/Al2O3) using the atomic layer deposition technique, and investigate the passivation quality and mechanism on c-Si surfaces. The BOx/Al2O3 stacks display excellent surface passivation on c-Si surfaces after annealing, superior to that of Al2O3 single layers. With the optimal BOx/Al2O3 passivation stack, we obtained a very low dark current density (J0) of 7.8 fA/cm2 (iVoc 725 mV) and 4.7 fA/cm2 (iVoc 714.6 mV) on industrial n-type (5.3 Ω cm) and p-type (3.0 Ω cm) Cz wafers, respectively. The BOx/Al2O3 stack also shows excellent passivation performance on boron-doped p+ emitters (110 Ω/sq), achieving a low J0 of 15.1 fA/cm2. The enhanced passivation quality of the BOx/Al2O3 stack can be attributed to the increased fixed negative charge density after thermal annealing. BOx/Al2O3 passivation stacks also can potentially act as an effective p-type dopant source for laser processing, which would be very desirable for high-efficiency c-Si solar cells.