Theoretica Study of Asymmetric Double D-π-A Organic Sensitizers for Efficient Dye-Sensitized Solar Cells

Three novel dye sensitizers that were based on asymmetric double D-π-A chains with phenoxazine (POZ) and diphenylamine (DPA) as electron donors and cyanoacetic acid (CA) and 2-(1,1- dicyanomethylene) rhodanine (RD) as electron acceptors (DCPR, DRPC, DRPR) were designed, theoretically investigated, and compared with the reference dye based on asymmetric double D-π-A chains (DCPC). Using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations, we gained insight into the factors responsible for the photovoltaic properties of the dye sensitizers. Due to the different HOMO levels of each donor and the different LUMO levels of each acceptor, the absorption spectrum of each dye showed different shapes. Among the dyes, DRPR showed a broader and more bathochromically shifted absorption band than the other dies. It also showed a higher molar extinction coefficient than that of the reference dye (DCPC). This work suggests optimizing the chain of electron donors and acceptors in dye sensitizers based on asymmetric double D-π-A chains would produce good photovoltaic properties for dye-sensitized solar cells (DSSCs).