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.

通过升温法合成了八面体 Ag8SnSe6 量子点（QDs），该合成过程涉及相应金属乙酸盐与硒脲在 250 °C 下于油胺溶液中进行反应，其中以 1-十二烷硫醇（DDT）作为封端配体。所得的量子点为具有立方晶格结构的球形颗粒。随着反应混合物中 DDT 用量的增加，从 0 至 0.23 mmol，Ag8SnSe6 量子点的大小从 7.8 nm 减小至 4.9 nm。获得的量子点的吸收光谱较为宽泛，且随着加入 DDT 用量的增加，吸收起始波长从约 1600 nm 蓝移至约 1300 nm。从吸收光谱的 Tauc 图中确定的能隙随着量子点尺寸从 7.8 nm 减小至 4.9 nm 而增加，从 0.82 eV 提升至 1.10 eV。光致电化学测量表明，固定在 ITO 电极上的 Ag8SnSe6 量子点在光照下产生光电流。光电流的作用光谱与相应的吸收光谱大致吻合，表明以近红外光激发的 Ag8SnSe6 量子点产生了光电流。光电流产生的起始电位位于 QDs 的价带顶（VBM）以上，约为 0.20–0.27 V vs. Ag/AgCl，这表明间隙态，作为光生载流子的捕获位点，位于价带顶之上，并介导电子和空穴向 ITO 电极的转移，分别产生阳极和阴极光电流。