Engineering highly efficient porphyrin sensitizers through metal, ligand and bridge modification: a DFT study

This work presents a systematic investigation of porphyrin sensitizers for application in dye-sensitized solar cells (DSSCs). Density functional theory calculations, including both static and time-dependent methods, were employed to evaluate a series of candidate dyes for their potential to achieve high power conversion efficiency. The well-established SM315 dye, known for its record-breaking PCE of 13%, was adopted as a reference point. A range of metal atoms including alkaline-earth and 3d transition metals were screened, Ca was identified as the most promising metal for light capture and conversion. Ca-porphyrin-based sensitizer was further modified by introducing different axial ligands and four distinct bridging units. The designed dyes exhibit red-shifted absorption spectra and optimal frontier orbital alignment with the semiconductor's conduction band, promoting efficient light capture and charge transfer. In addition to these core parameters, a comprehensive analysis of light harvesting efficiency (LHE), reorganization energy (λ), short-circuit current density (J_SC), exciton binding energy (EBE), open-circuit voltage (V_OC), electron transfer rate (k), polarization (α) and hyperpolarization (β_tot) collectively paint a clear picture of superior light capture, efficient charge transport dynamics, and minimized energy losses within the designed dyes. This ultimately translates to the remarkable power conversion efficiency (PCE) exceeding 27% achieved by the specifically designed dye with the Ca as metal atom, 4,4'-bipyridine as axial ligands and cyclopenta-1,3-diene as bridging unit, surpassing the performance of SM315 dye (13% PCE). This systematic study combines the design of high-performance porphyrin sensitizers through molecular engineering with a comprehensive investigation of their impact on DSSC function using advanced computational methods.