Bio-sensitized solar cells built from renewable carbon sources

Recent advances in materials science lead to the emergence of novel materials to address current energy and environmental challenges, such as energy-intensive manufacturing processes, use of hazardous materials, and greenhouse gas (GHG) emissions of photovoltaic (PV) technology. New materials that are more environmentally sustainable and abundant in nature are being integrated into PV technologies, especially in dye-sensitized solar cells. Carbon nanomaterials and biomolecules, specifically the photosystem I (PSI) and the bacteriorhodopsin (bR) proteins, are discussed in this review for bio-sensitized solar cells (bio-SSCs). Nanostructured carbon materials show enormous potential because of their allotropic diversity, compatible wide bandgap levels that facilitate light absorption, and excellent electrical properties, whereas the PSI and bR are promising as sensitizers because of their chromophores, high quantum yield, and chemical stability. This review addresses the role of these renewable materials for the development of bio-SSCs. The low photoconversion efficiency of bio-SSCs remains a challenge and is explained on energy mismatch, low surface density of sensitizer, and high-resistance interfacial electron transport between photoanode and electrolyte. By comparing the effect of various morphologies of photoanode semiconductors and protein modifications in the performance of bR-sensitized solar cells, we appraise how far bio-SSCs may progress in the future.