Critical review of metalloporphyrin drawbacks and additive adverse effects in porphyrin DSSCs toward high efficiency metal free porphyrin sensitizers

Porphyrins are highly conjugated organic systems well suited for dye-sensitized solar cell (DSSC) applications due to their broad absorption spectra and tunable photophysical properties. While metalloporphyrins have historically demonstrated high performance, they face significant challenges, including photobleaching, inefficient electron injection, poor energy level alignment, and limited long term stability. This review focuses on molecular engineering strategies designed to enhance the efficacy of metal free porphyrins in DSSCs. Key approaches include extending π conjugation to broaden light absorption into the near-infrared spectrum, modifying meso and β positions to prevent dye aggregation and optimize energy gaps, and designing asymmetrical push pull structures to facilitate directional charge transfer. Furthermore, the implementation of co-sensitization and the incorporation of bulky substituents are explored as methods to improve charge separation and retard charge recombination, respectively. The review also provides a comparative analysis of energy loss mechanisms in both metalloporphyrin and metal free systems, offering a critical assessment of their respective performance limitations and potential. This work underscores the promise of metal free porphyrins as a viable pathway toward more stable and efficient DSSC technologies.