Abstract
Dye-sensitized solar cells based on bacterial-based photosensitizers (bio-sensitized DSSCs) are promising bio-photoelectronic molecular devices exhibiting enhanced electron excitation, injection, and dye regeneration for efficient photon-to-electron quantum-conversion. Achieving high DSSCs performance via environmentally sustainable, cost-effective, and naturally-sensitized plant-based or bacterial-based biomolecules remains a challenge. Here, we provide a comprehensive study on the mechanisms involved in the utilization of biomolecular bacterial-based pigments (e.g. proteins and carotenoids) for an improved bio-sensitized DSSCs performance. Protein complexes and chlorophyll a/carotenoids are among many bio-photosensitizers demonstrating high incident photon-to-current efficiency (IPCE). Pigments molecular structure, donor-pi-acceptor conjugation, and anchoring groups have been discussed and attributed to theoretical dye HOMO-LUMO bandgaps and their corresponding bio-sensitized DSSCs IPCE. This review provides critical understanding of advancements towards natural photosensitization: (i) carboxyl/hydroxyl groups attached to acceptor segments provide firm attachment and rapid electron injection, (ii) proteins/carotenoids hybrid dyes induce visible-light photosensitivity and broaden absorbance, (iii) increased conjugated pi-bonds (n > 13) develop pigment visible-NIR absorption with intensified photoactivity, (iv) chromatophores integrated with bio-electrolyte provide a unidirectional flow of electrons, (v) reaction center (RC)-sensitized DSSCs have better optoelectronic properties than light-harvesting complex (LH2) due to its efficient charge separation, (vi) antioxidants hinder degradation of pigmented-photoanodes from UV radiation, (vii) solid-state redox improves device stability and dye neutralization; which all together would boost the dye sensitization performance in bio-sensitized DSSCs. The highest recorded IPCEs are found for TiO2-based DSSCs using plant-based coumarin (9%) and from [A. amentacea + P. pterocarpum] pigments (8.22%). Futuristically, we anticipate that these biologically-derived photosensitizers can be integrated into photoanodes for photoelectronic applications including DSSCs, multi junction cells, photodiodes, phototransistors, photodetectors, flexible bioelectronic films and clothes, bio-LEDs, and photo-tunneling junctions.