Single-Crystal Growth and Characterization of the Chalcopyrite Semiconductor CuInTe₂ for Photoelectrochemical Solar Fuel Production

Abstract

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 firstprinciples 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.

Prediction of Tunable Spin-Orbit Gapped Materials for Dark Matter Detection

“…However, the larger band gap predicted by hybrid functionals is in better agreement with the experimentally measured values, as expected for regular semiconductors. 45,47,49 Including SOC worsens the prediction of E g in comparison to experiment (CuInTe 2 has an optical band gap of 0.9 eV; HSE06 predicts 0.74 eV without SOC and 0.54 eV with SOC), but the effects are needed to reveal features of the experimentally measured band structure such as splitting of the valence band. 45,49 Regardless, the band gaps of the compounds have been comprehensively determined by experiment, and, being of the order of an eV, are too large for our desired absorption of DM with meV masses or scattering of DM with keV masses.…”

“…42,43 The calculated lattice parameters of the three copper indium chalcogenides are well matched to reported experimental values (given in SI Table 2). The chalcopyrite family have previously been considered for light-harvesting devices including solar cells, solar fuel cells and photodetectors, [44][45][46][47][48][49] and CuInTe 2 has also been suggested as a promising thermoelectric. 50 Electronic structure: The electronic band structures and density of states (DOS) of CuInTe 2 as calculated with the PBE functional with SOC both included and not included are shown in Figure 2a-b.…”

The band structure of CuInTe2 studied by optical reflectivity

“…4 Furthermore, the steepness of energy-momentum dispersion relations of CuInTe2, experimentally determined in ref. [5], results in carrier mobility exceeding 800 cm 2 V -1 s -1 which significantly greater than those observed for other chalcopyrites making this compound highly suitable for light-harvesting applications whereas the energies of its valence and conduction bands make CuInTe2 a strong candidate as a material for converting sunlight into sustainable hydrogen energy by photoelectrocatalytic water splitting.…”

“…19 Room temperature measurements demonstrate a reduction of Eg. 5 However, no reports on CuInTe2, exhibiting clear splitting of the A and B free excitons, can be found in the literature as yet.…”

A Magneto‐Reflectivity Study of CuInTe2 Single Crystals

“…[8] A recent study of the electronic structure of CuInTe 2 carried out using angular-resolved photoelectron spectroscopy demonstrated a remarkable steepness of the energy-momentum (E-k) dispersion relations of the valence band in this compound. [9] This can be very beneficial for solar cells based on this material.…”