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

Abstract 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.