Solution-phase Synthesis and Photoelectrochemical Properties of Ag₈SnSe₆ Quantum Dots with Different Sizes (Supporting Information)

Ternary Ag₈SnSe₆ quantum dots (QDs) were synthesized via a heating-up method in which the reaction of corresponding metal acetates and selenourea was carried out at 250 °C in oleylamine containing 1-dodecanethiol (DDT) as a capping ligand. The obtained QDs were spherical particles with a cubic Ag₈SnSe₆ crystal structure. The size of Ag₈SnSe₆ QDs decreased from 7.8 to 4.9 nm as the amount of DDT in the reaction mixture was increased from 0 to 0.23 mmol. The absorption spectra of obtained QDs were broad, and the wavelength of the absorption onset was blue-shifted from ca. 1600 nm to ca. 1300 nm with an increase in the amount of DDT added. The energy gap determined from Tauc plots of the absorption spectra increased from 0.82 eV to 1.10 eV with a decrease in the QD size from 7.8 to 4.9 nm. Photoelectrochemical measurements revealed that Ag₈SnSe₆ QDs immobilized on ITO electrodes generated photocurrents under light irradiation. The action spectra of photocurrents roughly matched the corresponding absorption spectra, indicating that Ag₈SnSe₆ QDs photoexcited with near-IR light generated photocurrents. The onset potentials of photocurrent generation were located at 0.20–0.27 V vs. Ag/AgCl for the QDs. This suggested that intragap states, acting as trap sites for photogenerated carriers, were located above the valence band maximum (VBM) level of QDs and mediated the electron and hole transfers to ITO electrodes, generating anodic and cathodic photocurrents, respectively.