Rational Design of Phenothiazine-Based Organic Dyes for Dye-Sensitized Solar Cells: The Influence of π-Spacers and Intermolecular Aggregation on Their Photovoltaic Performances

Power conversion efficiency (PCE) is one of the important factors in influencing the overall performance of dye-sensitized solar cells (DSSCs), and precise prediction of PCE is a feasible strategy for preparing highly efficient DSSCs devices. In this work, we designed a series of phenothiazine-based organic dyes by introducing different pi-spacers including the 4-isopropyl-4H-dithieno[3,2-b:2',3'-d]pyrrole (DTP) and 2,7-dihydronaphtho[1,2-d:5,6-d'] diimidazole (NDI) to tune their photovoltaic properties. The present studies reveal that the PCE value of the DTP-based dye is estimated to be 8.55%, in excellent agreement with the experimentally available value (8.19%) observed in the reported analogue. In comparison to DTP, the strong electron-deficiency NDI group induces a remarkable red-shifting of maximum absorption band, broadening the optical absorption into the near-infrared region. As a consequence, the NDI-based dye achieves an impressive PCE value of 15.51%, which is expected to be a potential organic dye applied in DSSCs.