Slicing Diamond-A Guide to Deriving sp³ -Si Allotropes

Area of Science:

• Materials Science
• Solid-State Physics
• Computational Chemistry

Background:

• Silicon is crucial for solar cells, but its low efficiency necessitates high material usage.
• Developing silicon allotropes with higher efficiency and direct electronic band gaps is a key research goal.
• Existing reports of new silicon structures often lack context and coherent classification.

Purpose of the Study:

• To classify reported silicon allotropes and establish structural relationships with known Zintl phases.
• To introduce a systematic approach, termed a "construction kit," for generating tetrahedral silicon allotropes.
• To explore novel silicon structures with potential for enhanced solar cell performance.

Main Methods:

• A "chemi-inspired" approach using a "construction kit" based on modifications of the cubic diamond structure.
• Topological and structural analyses to establish relationships between silicon allotropes and Zintl phases.
• Density Functional Theory (DFT) calculations at the PBE0/SVP level of theory for structural and electronic property analysis.

Main Results:

• Classification of numerous tetrahedral silicon allotropes derived from the cubic diamond structure.
• Identification of ten low-energy silicon structures, five of which are newly reported.
• Observation of quasi-direct band gaps in some of the novel silicon structures.
• Demonstration of extensive structural (topological) relationships between silicon allotropes and Zintl phases, including phase transitions.

Conclusions:

• The "construction kit" approach effectively classifies and generates novel silicon allotropes.
• The identified low-energy silicon structures, including new ones, show promise for improved solar cell applications.
• This method provides a framework for understanding and discovering new tetrahedral silicon structures and their relationships to known materials.