Beyond traditional photosensitizers in DSSCs: harnessing the optical properties of noble metal nanoclusters

In an effort to reduce the carbon footprint, green alternative technologies such as dye sensitized solar cells (DSSCs) are being developed. In this evolving field, the search for efficient photosensitizers that can enhance light harvesting, charge transfer, and interfacial stability remains a central challenge. One promising direction for their development includes nanostructured materials, in particular, atomically precise noble metal bio-nanoclusters (bio–NCs). Because of their unique properties that can bridge the gap between classical bulk and quantum systems, they offer great potential as novel, non-traditional photosensitizers. In this Perspective, a computational chemistry-driven outlook is provided, developed in close collaboration with experimental insights, on recent advances in the study of noble metal bio–NCs. Emphasis is placed on their nonlinear optical (NLO) properties – an aspect crucial for DSSC performance, yet often overlooked. Three proposed photosensitizer systems are addressed: cyanidin–Ag₃ hybrid, Ag₃–DNA, and liganded Ag₂₅. Furthermore, heterometal atom doping has been discussed as a strategy to tune the electronic structure of NCs, thereby influencing their stability, catalytic properties, and photoluminescence. Additionally, as interactions with the semiconductor surface play an important role in charge separation, the anchoring modes of these systems on a TiO₂ model are proposed. By integrating insights from time-dependent density functional theory (TDDFT) with emerging experimental perspectives, this work aims to provide a deeper understanding of noble metal bio–NC properties towards revival in solar energy research.