Phenothiazine derivatives-based D–π–A and D–A–π–A organic dyes for dye-sensitized solar cells

Abstract

D–π–A and D–A–π–A-structured organic dyes represent different developmental directions of photosensitizers in dye-sensitized solar cells (DSSCs). In this work, two phenothiazine derivatives-based D–π–A and D–A–π–A-structured organic dyes have been synthesized and applied in DSSCs. The physical and electrochemical properties of both dyes have been investigated systematically. The results show that the D–A–π–A-structured dye exhibits a broader spectrum response but lower molar coefficient of extinction when compared to the D–π–A-structured dye. Regarding photovoltaic performance, the D–π–A-structured dye yields a higher efficiency (η) of 7.5% with a higher short-circuit current density (J_sc) of 16.36 mA cm⁻² and open-circuit voltage (V_oc) of 706 mV than that of the D–A–π–A-structured dye. Incident photon-to-electron conversion efficiency (IPCE) studies and impedance analysis also support these results. These results demonstrate that the phenothiazine derivatives-based D–π–A-structured organic dyes can compete with, and even exceed, D–A–π–A-structured organic dyes under the same test conditions.