This work reports a systematically theoretical study concerning the design of D-pi-A organic dyes for DSSC. Two elaborate strategies, namely the rigidity of dithiophene and introduction of strong electron rich/deficient moieties, are proposed. By using the state-of-the-art theoretical calculations, the general influences of fastening atoms (C, N, and O) for pi-spacer rigidification in planar amine-based organic dyes are firstly investigated and elucidated. The properties of isolated dye, dye/(TiO2)(38), and dye-I-2 interaction are discussed in detail. The results show that, compared with the P2T dye containing dithiophene pi-spacer, its three counterparts with rigidified dithiophene pi-spacers would present the improved absorption properties. We further demonstrate that incorporation of O-bridged dithiophene moiety into the pi-spacer was promising to challenge the photoelectric conversion efficiency 8.29% of P2T. Furthermore, benzothiadiazole (BTD) and 3,4-ethylenedioxythiophene (EDOT) moieties are the well-known pi-skeletons that can effectively tune the electronic structure properties and the light-harvesting ability. Subsequently, a series of dyes are designed through introducing the BTD and EDOT groups into pi-spacer. The calculated results reveal that the dye with the incorporation of EDOT moiety would be more beneficial for photocurrent and photovoltage performance. The current theoretical studies are expected to be very relevant for the molecular design of D-pi-A organic dyes in DSSC. (C) 2014 Elsevier B.V. All rights reserved.