The global consumption of fossil fuels is steadily increasing, leading to their inevitable exhaustion. This escalating reliance on these nonrenewable resources necessitates the development of sustainable alternatives. Research efforts are actively focused on identifying and implementing renewable energy sources alongside efficient technologies for energy storage and conversion. Solar radiation is considered one of the most promising options among the available renewable energy resources. Traditional solar cells made from silicon are efficient but have an energy demanding and complicated manufacturing process which may lead to hazardous chemical spills. Organic solar cells have therefore become a hot research area thanks to their low production cost, lightweight, and flexibility, and hence many applications, such as indoor use or attached to clothing to power personal electronic devices. Lignin, a ubiquitous organic constituent of plant cell walls, shows great potential as a material for creating stable and environmentally benign organic solar cells. Lignin nanomaterials are proving to be versatile players in the world of energy conversion. In solar cells (photovoltaic devices), they’re being used in various ways, including as light absorbers, electrolytes, and components for electrodes that help transport positive charges (holes). Novel approaches in the field of lignin-based material development have led to their successful implementation in photovoltaic devices. This chapter reviews lignin-based materials for photovoltaic applications in solar energy conversion. Finally, important challenges and prospects in this field are presented, which are expected to contribute to the rational design of advanced economic materials based on lignin for sustainable development.