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 TiO2and its stacked combinations with amorphous silicon or SiO2passivation layers. The relative effectiveness of these contact schemes is quantified under practical concerns of Fermi-level pinning (FLP) and interfacial defects. For a standard TiO2/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 TiO2. With the insertion of an ultrathin SiO2layer, the SiO2/TiO2/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 SiO2layer, 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× 1012cm-2eV-1. In contrast, the cell performance for TiO2/Al stack degrades due to surface recombination losses for interfacial defect density above ~1 × 1010cm-2eV-1. These quantitative insights provide valuable understanding of the published experimental data and provide useful guidelines for the design of TiO2-based contact stacks.