A Novel n-Type Organosilane-Metal Ion Hybrid of Rhodamine B and Copper Cation for Low-Temperature Thermoelectric Materials.

An n-type organosilane-metal ion hybrid of Rhodamine B-silane and copper cation (Cu-RBS) was investigated as a low-temperature thermoelectric material. Computational analysis revealed the most likely localized binding site of Cu2+ was to the Rhodamine B core and provided predictions of molecular orbitals and electrostatic potentials upon complexation. The concentration-dependent optical absorption and emission spectra confirmed the effective metal-ligand charge transfer from Cu2+ to the xanthene core of RBS, indicating the potential for improved electrical properties for the complex relative to RBS. The electrical conductivity and Seebeck thermoelectric (TE) behavior were evaluated and compared with its precursor complex of Rhodamine B and copper cation. While a moderately high electrical conductivity of 4.38 S m-1 was obtained for the Cu-RBS complex, the relatively low Seebeck coefficient of -26.2 μV/K resulted in a low TE power factor. However, compared to other organic doped materials, these results were promising toward developing n-type thermoelectric materials with no doping agents. Both phase segregation and thin film heterogeneity remain to be optimized; thus, the balance between Cu2+ domains and RBS domain phases will likely yield higher Seebeck coefficients and improved power factors.