Design of new metal-free dyes for dye-sensitized solar cells: A first-principles study

Five new metal-free dyes with acceptor-pi-donor (A-pi-D) structure are studied using first-principles calculation based on density functional theory. Benzothiadiazole (BTD) and triphenylamine (TPA) were chosen, respectively, as an acceptor and a donor with 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) as a pi linker. The linker was further modified by -CH=CH- resulting in a red-shift with improved absorption spectra caused by the smaller energy gap and the increased orbital hybridization. The designed dyes are found to exhibit wide absorption spectra, high molar extinction coefficients, desirable orbital distributions, and good energy levels alignment, and hence can have potential applications in dye-sensitized solar cells. (C) 2012 Elsevier B.V. All rights reserved.