Structural planarity and conjugation effects of novel symmetrical acceptor–donor–acceptor organic sensitizers on dye-sensitized solar cells

In this study two series of novel symmetrical acceptor–donor–acceptor organic sensitizers containing 3,6- and 2,7-functionalized carbazole cores, respectively, connected to two anchoring cyanoacrylic acid termini via thienyl linkers were synthesized. The effect of the molecular planarity originating from the 3,6- and 2,7-functionalized carbazole cores on the performance of corresponding solar cells were investigated. Molecular orbital analyses revealed the characteristics of the carbazole-based highest occupied molecular orbitals and acid-based lowest unoccupied molecular orbitals. Time-dependent density functional theory calculations allowed us to assign the electronic transitions (>90%) of the low energy bands. Among these new dyes, the highest power conversion efficiency of 4.82% was obtained in a dye-sensitized solar cell device under standard AM 1.5 sunlight with an open-circuit voltage of 0.61 V, a short-circuit photocurrent density of 12.66 mA cm−2 and a fill factor of 0.62.

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► Symmetrical A–D–A organic sensitizers with various carbazole cores were synthesized.
► Electronic transitions of low energy bands could be assigned by TD-DFT calculations.
► The DSSC device containing our optimum dye possessed the highest PCE value of 4.82%.