Ag${}^{+}$ ion doped on the CdSe quantum dots for quantum-dot-sensitized solar cells' application

Quantum dots are drawing great attention as a material for the next generation solar cells because of the high absorption coefficient, the tunable bandgap, and multiple excitons' generation effect. In this paper, Ag${}^{+}$ ions doped on the CdSe quantum dot by mixing molar concentrations of 0.005 M, 0.01 M, 0.015 M, 0.02 M, and 0.026 M of AgNO${}_3$ with Cd(CH${}_3$COO)${}_2$·2H${}_2$O anion source. TiO2/CdSe:Ag${}^{+}$ multiple layers were obtained by the successive ionic layer absorption and reaction, as the TiO${}_2$ film was dipped in the CdSe:Ag${}^{+}$ quantum-dot solution. The morphological observation and crystalline structure of photoanode films were characterized by the field-emission scanning electron microscopy and X-ray diffraction. The electrochemical performance of photoelectrode was studied using the electrochemical impedance spectra. As a result, we have succeeded in designing a cell with the high efficiency of 2.72%. In addition, the optical properties, the direct optical energy gap, and both the conduction band and valence band levels of the compositional CdSe:Ag${}^{+}$ were estimated using theory of Tauc and discussed details. This theory is useful for us to understand the alignment energy structure of the compositions in photoelectrodes, in particular, the conduction band and valence band levels of CdSe: Ag${}^{+}$ nanoparticles.