TiO2has been identified as a promising electron
transport
layer in Si solar cells. Experiments have revealed that the Si:TiO2interface undergoes structural changes depending on how it
was fabricated. However, less is understood about the sensitivity
of electronic properties, such as band alignments, to these changes.
Here, we present first-principles calculations of band alignments
between Si and anatase TiO2, investigating different surface
orientations and terminations. By calculating vacuum-level alignments,
we observe a large band offset reduction of 2.5 eV for the O-terminated
Si slab compared to other terminations. Furthermore, a 0.5 eV increase
is found for the anatase (101) surface compared to (001). We compare
the band offsets obtained through vacuum alignment with four different
heterostructure models. Even though the heterostructure models contain
an excess of oxygen, their offsets agree well with vacuum-level alignments
using stoichiometric or H-terminated slabs, and the reduction in band
offsets seen for the O-terminated Si slab is not observed. Additionally,
we have investigated different exchange-correlation treatments including
PBE + U, postprocessingGWcorrections, and the meta-GGA
rSCAN functional. We find that rSCAN provides more accurate band offsets
than PBE, but further corrections are still required to achieve <0.5
eV accuracy. Overall, our study quantifies the importance of surface
termination and orientation for this interface.