First Principles Calculations of Bonding and Charges at the Al 2 Interface in a c-Si/SiO 2 O 3 Interface in a c-Si/SiO 2 /am-Al 2 O 3 Structure Applicable for the Surface Passivation of Silicon-Based Solar Cells

We present the electronic properties of the crystalline-silicon (c-Si)/SiO 2 /am-Al 2 O 3 interface using first principles calculations. First, we generate a relaxed $3\,\times \,1$ supercell of amorphous (am)-Al 2 O 3 , which we use as a benchmark structure, validated through the experimental data. Next, using this, we generate a relaxed supercell of the c-Si/am-Al 2 O 3 interface with a thin layer of SiO 2 sandwiched between them. With this structure, we demonstrate that at the interface section, the percentage of the tetrahedral coordinated Al atoms decreases while that of the octahedral coordinated Al atoms increases compared with the Al atoms present in the bulk section of the interface structure. In addition, on an average, the effective charges on Al atoms increase by 0.19|e|, while for O atoms, the effective charges decrease by 0.02|e|. This change in the bonding distribution and charges near the interface might be responsible for the occurrence of negative fixed charges, also confirmed by various experiments involving am-Al 2 O 3 passivation in Si-based solar cells. The origin of these negative charges on the other hand is under discussion and speculation.