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

D-pi-A and D-A-pi-A-structured organic dyes represent different developmental directions of photosensitizers in dye-sensitized solar cells (DSSCs). In this work, two phenothiazine derivatives-based D-pi-A and D-A-pi-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-pi-A-structured dye exhibits a broader spectrum response but lower molar coefficient of extinction when compared to the D-pi-A-structured dye. Regarding photovoltaic performance, the D-pi-A-structured dye yields a higher efficiency (h) 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-pi-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-pi-A-structured organic dyes can compete with, and even exceed, D-A-pi-A-structured organic dyes under the same test conditions.