Computational quantum chemistry on the photoelectric characteristics of semiconductor quantum dots and biological pigments

This paper intends to use semiconductor quantum dots (cadmium sulphide-CdS) and/or biological pigments (chlorophyll-a derivatives) to replace those expensive ruthenium (Ru) dyes in photoelectrochemical solar cells. Based on the computational quantum chemistry, the molecular structures of (CdS) n (n=1∼22) clusters and chlorophyll-a derivatives (chlorin-H+3 and chlorin-H+17) are configured and optimized. Density functional theory (DFT) of the first principles calculations, which chose B3LYP (Becke 3-parameter Lee-Yang-Parr) and PBE (Perdew-Burke-Ernzerhof) exchange correlation functionals, is employed. Photoelectric properties, such as: molecular orbital, density of state (DOS), highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and resultant band gaps are predicted. The band gaps calculated from the computer modeling are close to experiments. It is concluded that we can enhance the sunlight absorption by mixing different diameters of semiconductor quantum dots. Also biological pigment, chlorin-H+3 , has a suitable bonding structure with the TiO2 electrode. Broad light absorption spectra and cheap price are their major characteristics. © 2011 Tech Science Press.