Organic dyes containing oligo-phenothiazine for dye-sensitized solar cells

Abstract

A series of organic dyes containing oligo-phenothiazine were synthesized and used effectively on the fabrication of dye-sensitized solar cells (DSSCs). In these compounds the phenothiazine moiety functions both as an electron donor and as a π-bridge. These materials exhibit considerably high values of open-circuit voltage (V_oc) ranging from 0.78–0.83 V under an AM1.5 solar condition (100 mW cm⁻²). Two kinds of substituents, i.e., hexyl and hexyloxyphenyl groups, were added onto the N(10) of phenothiazine for comparison. The best device displayed a short-circuit current (J_sc) of 14.3 mA cm⁻², an open-circuit voltage (V_oc) of 0.83 V, a fill factor (FF) of 0.65, corresponding to an overall conversion efficiency of 7.78%. Their photophysical properties were analyzed with the aid of a time-dependent density functional theory (TDDFT) model with the B3LYP functional. The electronic nature of the devices was further elucidated by using electrochemical impedance spectroscopy.