Biochar from Lignocellulosic and Microalgae Biomass: Properties and Potential for Emerging Photovoltaic Devices

This review investigates biomass-derived carbons as sustainable materials for photovoltaic (PV) applications. The work links their physical and chemical properties, such as porosity, conductivity, and surface chemistry to the performance of PVs. The results show that nitrogen- and oxygen-rich biochars can act as efficient electrodes, charge transport layers, and interfacial modifiers. Biomass-employed PVs achieved power conversion efficiencies (PCEs) up to 23%. Key circular economy (CE) aspects, including sustainability, toxicity, environmental safety, and the need for rigorous life cycle assessment (LCA) were addressed. Carbon-based electrodes may reduce selected environmental burdens by lowering reliance on precious metals and fossil-derived carbon materials. Comparative LCA evidence shows that the net benefit depends on feedstock selection, pyrolysis and activation energy demand, fabrication route, device lifetime, and end-of-life (EoL) recovery. Microalgae-derived carbons show high potential due to their original nitrogen content and CO ₂ capture ability. However, their ash content and activation process still require optimization. The review outlines a framework for integrating biochar into circular PV technologies and provides recommendations for designing recyclable and environmentally safe biomass-employed PVs.