Optoelectronic performance and co-sensitized excited states characteristics of organic dyes with naphthobisthiadiazole and benzothiadiazole

Photosensitizer systems play a crucial role in light absorption and charge transfer processes. Designing and selecting dye molecules with exceptional photoelectric features remains a significant scientific challenge in the realm of solar cell research. The paper explores the photovoltaic properties of two D-A'-π-A dyes (CS-70 and CS-72) both individually and after co-sensitization with chlorophyll derivatives, utilizing density functional theory (DFT) and time-dependent density-functional theory (TD-DFT) methods. The monomeric dye molecules share the same donor and conjugated bridge but differ in their auxiliary receptors (benzothiadiazole and naphthobisthiadiazole). Firstly, the study investigates the impact of various auxiliary acceptors on the properties of the dye molecules by analyzing their geometrical structure, frontier molecular orbitals, spectral properties, chemical reaction parameters, intramolecular charge transfer, electron injection, density of projected states, and dye regeneration. A detailed explanation for the superior performance of CS-72 is provided. Furthermore, a solar cell evaluation model was developed for the short circuit current density (Jsc), open circuit voltage (Voc), and photoelectric conversion efficiency (PCE) of the single dye molecule. Subsequently, simulations of the co-sensitized molecules with chlorophyll are performed, focusing on structure, excited state properties and charge transfer, suggesting that co-sensitization enhances spectral properties, light-trapping, and regeneration abilities, and long-range charge transfer between the dye molecules and chlorophyll can be found. The results also demonstrate that the Jsc of the co-sensitized molecules were improved, which facilitates the realization of a higher PCE. This study provides theoretical support for the potential of co-sensitizing dye molecules with chlorophyll to enhance solar cell efficiency, offering valuable insights for the future development of green, cost-effective, and efficient solar cells.