Combined experimental and DFT computational study of the organic photosensitizer based on dithiophene combined with bis-dimethylfluoreneaniline

An organic dye (PH-1), in which bis-dimethylfluoreneaniline (BDFA) acts as a single electron donor and dithiophene groups as double electron acceptors, has been synthesized for use in dye sensitized solar cells (DSSCs). The other dye (PH-2) carrying one donor with one acceptor on meta-position has also been synthesized for comparison and the effect of the donor position of the dye has been investigated. The geometries and electronic structures of the dyes are elucidated by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The PH-1 and PH-2 dyes show their power conversion efficiencies of 3.04 and 4.06%, short circuit current densities of 6.2 and 7.8 mA cm−2, open circuit voltage of 644 and 689 mV, and fill factors of 76 and 75%, respectively. The TD-DFT computational study demonstrates that the excited states and localized electronic structures of the dyes renders the electron injection from dyes to TiO2 conduction band inefficient, compared to the well-known dye (JK-2) carrying one donor with one acceptor on para-position.