Modeling of TiO2-Based Electron-Selective Contacts for Crystalline Silicon Solar Cells

Contact selectivity is one of the key requirements for maximizing the efficiency of solar cells. Here, we computationally explore the electron-selective contact for crystalline silicon (c-Si) solar cells based on TiO
₂
and its stacked combinations with amorphous silicon or SiO
₂
passivation layers. The relative effectiveness of these contact schemes is quantified under practical concerns of Fermi-level pinning (FLP) and interfacial defects. For a standard TiO
₂
/Al contact stack on c-Si, a relatively high Schottky barrier (~0.5 eV) typically exists due to FLP which can increase the series resistance and degrades fill factor (FF) at low-to-moderate doping in TiO
₂
. With the insertion of an ultrathin SiO
₂
layer, the SiO
₂
/TiO
₂
/Al stack can mitigate the parasitic Schottky effect on series resistance through its better pinning factor, resulting in ~5% absolute increase in the FF. Moreover, by introducing a field-effect passivation through the SiO
₂
layer, the surface concentration of the minority carriers can be suppressed and the associated surface recombination losses can be minimized for interfacial defect density up to ~1× 10
¹²
cm
^-2
eV
^-1
. In contrast, the cell performance for TiO
₂
/Al stack degrades due to surface recombination losses for interfacial defect density above ~1 × 10
¹⁰
cm
^-2
eV
^-1
. These quantitative insights provide valuable understanding of the published experimental data and provide useful guidelines for the design of TiO
₂
-based contact stacks.