BODIPY-Based Macrostructures: A Design Strategy toward Enhancing the Efficiency of Dye-Sensitized Solar Cells

Among the metal-free dyes, boron dipyrromethene (BODIPY) has attracted much attention in the solar cell industry due to its thermal stability and tunable electronic and photophysical properties. However, the low power conversion efficiency of dye-sensitized solar cells based on BODIPY has limited their widespread application. Accordingly, different types of structural modifications have already been proposed to improve the photophysical properties of the BODIPY dyes. In this study, we used the strategy of constructing BODIPY-based covalent macrostructures by integrating two BODIPY subunits via a pi-linker in linear and cyclic configurations. To this end, various types of the pi-linkers including butadiyne, phenyl, and thiophene derivatives are considered. The structural, electronic, and optical properties as well as the photovoltaic performance of BODIPY dimers are theoretically calculated within DCM solvent. The results indicate that for a given linker, the BODIPY dimers with a linear configuration show better performance as compared to their macrocyclic counterparts. The reason is the enhancement of pi-conjugation length, higher light harvesting ability, and proper charge carrier separation in linearly linked BODIPYs. In the cyclic series, the dyes incorporating phenyl linkers exhibit greater power conversion efficiency of up to 9%. For the dyes with a linear configuration, the involvement of a thienyl-thiophene bridge results in lower charge recombination and enhances the efficiency by up to 15%, which are expected to be potential candidates for organic dyes applied in DSSCs.