Size-dependent properties of sonochemically synthesized three-dimensional arrays of close-packed semiconducting AgBiS2 quantum dots

3D arrays of close-packed AgBiS2 quantum dots (QDs) in thin film form were synthesized for the first time using novel, convenient sonochemical approach. Structural, optical, and photoelectrical properties of the synthesized material were investigated with an emphasis on their dependence on crystal size. The sonochemically synthesized AgBiS2 colloidal crystals have an average QD radius of 4.2 nm, twice as small compared to the QD solid obtained without ultrasonic irradiation. The optical band gap energy of sonochemically synthesized AgBiS2 QD thin films of 1.40 eV is strongly blue-shifted in comparison to that of the macrocrystal (0.90 eV) and that of nanostructured films synthesized by conventional chemical route (1.10 eV). Upon annealing, E-g exhibits a red shift to 1.00 eV. Spectral dependence of stationary nonequilibrium conductivity of the 3D QD assemblies suggests that the thin films' photoconductivity is modulated by the intercrystalline barrier height decrease. Eg of the films calculated on the basis of photoconduction spectral response in the low-absorption region is 1.18 eV. Thermal band gap energy of the films is 1.10 eV, whereas both the variable range hopping conduction and thermionic emission mechanisms are predominant in the overall intercrystalline charge carrier transport through 3D QD assemblies.