New D–D–π–A type organic dyes having carbazol-N-yl phenothiazine moiety as a donor (D–D) unit for efficient dye-sensitized solar cells: experimental and theoretical studies

Abstract

A series of novel organic dyes (CPhTnPA, n = 0–2) with the D–D–π–A structural configuration incorporating carbazol-N-yl phenothiazine moiety as a donor (D–D) unit, phenyl oligothiophenes as a π-linker and cyanoacrylic acid as both electron-acceptor and anchoring group were synthesized and characterized for dye sensitized solar cells. Detailed investigation on the relationship between the structure, spectral and electrochemical properties, and performance of DSSC was described here. Time dependent density functional theory (TDDFT) calculations have been performed on the dyes, and the results showed that both electron donors (D–D) can contribute to electron injection upon photo-excitation, either directly or indirectly by internal conversion to the lowest excited state. Dye-sensitized solar cells (DSSCs) using dyes as the sensitizers exhibited good efficiencies. In virtue of co-sensitization, the CPhT2PA based solar cell can achieve photovoltaic efficiency as high as 7.78% (J_SC = 15.22 mA cm⁻², V_OC = 0.74 V and FF = 0.69) which reached 95% with respect to that of the reference N719-based device (8.20%) in parallel investigations.