Single-Crystal Growth and Characterization of the Chalcopyrite Semiconductor CuInTe ₂ for Photoelectrochemical Solar Fuel Production

Transition-metal chalcogenides are a promising family of materials for applications as photocathodes in photoelectrochemical (PEC) H ₂ generation. A long-standing challenge for chalcopyrite semiconductors is characterizing their electronic structure, both experimentally and theoretically, because of their relatively high-energy band gaps and spin-orbit coupling (SOC), respectively. In this work, we present single crystals of CuInTe ₂ , whose relatively small optically measured band gap of 0.9 ± 0.03 eV enables electronic structure characterization by angle-resolved photoelectron spectroscopy (ARPES) in conjunction with first-principles calculations incorporating SOC. ARPES measurements reveal bands that are steeply dispersed in energy with a band velocity of 2.5-5.4 × 10 ⁵ m/s, almost 50% of the extremely conductive material graphene. Additionally, CuInTe ₂ single crystals are fabricated into electrodes to experimentally determine the valence band edge energy and confirm the thermodynamic suitability of CuInTe ₂ for water redox chemistry. The electronic structure characterization and band edge position presented in this work provide kinetic and thermodynamic factors that support CuInTe ₂ as a strong candidate for water reduction.