First-Principles Band Alignments at the Si:Anatase TiO₂ Interface

Area of Science:

• Materials Science
• Solid State Physics
• Renewable Energy

Background:

• Titanium dioxide (TiO2) is a key material for electron transport layers in silicon (Si) solar cells.
• The Si:TiO2 interface structure changes with fabrication, affecting electronic properties like band alignment.
• Understanding these changes is crucial for optimizing solar cell performance.

Purpose of the Study:

• To investigate the impact of surface orientation and termination on Si:TiO2 band alignments using first-principles calculations.
• To compare different theoretical methods for calculating band offsets.

Main Methods:

• First-principles calculations of band alignments between Si and anatase TiO2.
• Investigation of various surface orientations and terminations (e.g., O-terminated Si).
• Comparison of vacuum-level alignment with heterostructure models and different exchange-correlation functionals (PBE + U, GW, rSCAN).

Main Results:

• Oxygen termination of Si slabs significantly reduces band offset (up to 2.5 eV).
• Anatase TiO2 (101) surface shows a 0.5 eV higher band offset compared to (001).
• Heterostructure models generally agree with vacuum-level alignments for stoichiometric/H-terminated slabs, but miss the O-termination effect.
• The rSCAN functional offers improved accuracy over PBE, but further corrections are needed for <0.5 eV precision.

Conclusions:

• Surface termination and orientation critically influence Si:TiO2 band alignments.
• Accurate theoretical modeling requires careful consideration of interface structure and computational methods.
• Findings provide insights for designing efficient Si solar cells with TiO2 electron transport layers.