Precision Synthesis of I-III-VI Ternary Semiconductor Nanoclusters via Self-Limiting Cation Exchange

Ternary I-III-VI semiconductors are important materials because of their environmental compatibility and broad tunability. However, achieving atomic-level control of multinary semiconductor materials remains a major challenge. Here, we report the precision synthesis of ternary nanoclusters with atomically defined stoichiometry, structure, and surface via self-limiting cation exchange. Specifically, the reaction between a Cu₂₆Se₁₃(PR₃)₁₄ template cluster and an InCl₃-PR'₃ complex produces a partially exchanged Cu₆In₈Se₁₃Cl₄(PR'₃)₁₂ cluster in high purity and near-unity yield. The ternary cluster retains the icosahedral Se₁₃ anion framework, with In³⁺ and Cu⁺ cations self-assembled into a pseudo-core/shell heterostructure. All the phosphines bind to the outer-edge Cu⁺, while all the chlorides coordinate to the inner-facet In³⁺. The reaction is further generalized to Ga³⁺, producing an analogous Cu₆Ga₈Se₁₃Cl₄(PR₃)₁₂ cluster. Such self-limiting cation exchange and precise assembly of multinary cations and ligands can be attributed to charge, coordination, steric, and symmetry factors. Theoretical calculations reveal that Cu⁺ and In³⁺/Ga³⁺ contribute significantly to the occupied and unoccupied frontier orbitals, respectively, leading to a broad absorption band with charge-transfer character. The clusters can be sintered to form bulk semiconductors with well-controlled stoichiometry, demonstrating their potential as precise precursors for solution processing of multinary semiconductors. We expect that atomically defined cation-exchange reactions will open opportunities for precision engineering of complex multinary semiconductor materials.