Effect of Thiophene Spacer Position in Carbazole-Based Dye-Sensitized Solar Cells on Photophysical, Electrochemical and Photovoltaic Properties

The synthesis, photophysical and electrochemical properties, and photovoltaic performances in dye-sensitized solar cells (DSSCs) of five new metal-free organic sensitizers with a carbazole moiety as the electron donor are reported. The compounds contain a thiophene at various positions and a cyanoacrylic acid unit as the electron acceptor. The position of the thiophene moiety affected both the photophysical and electrochemical properties, leading to conversion efficiencies of 1.44 to 4.57 % under AM 1.5 solar conditions (100 mW cm^–2). The best performance and longest electron lifetime were found when a thiophene was located on both donor and acceptor sites. The DSSC showed a short-circuit current (J_sc) of 8.59 mA/cm², an open-circuit photovoltage (V_oc) of 0.75 V, and a fill factor (FF) of 0.71. The position of the π-conjugated bridges not only affects the absorption spectra and the energy levels of the sensitizers, but also adjusts the electron lifetime.