Single-Chromophore Homojunction Organic Solar Cells: A Path to Simplicity and Efficiency

Recent advances in single-chromophore homojunction organic solar cell (SCH OSC) performance begin to challenge the prevailing notion that efficient OSCs will always require a bulk heterojunction light-absorbing layer, although their efficiencies still lag behind the best multicomponent devices. These homojunction devices rely on films composed of a single chromophore material to perform all the key photovoltaic functions: light absorption, exciton dissociation, and charge transport. The advances have been made through a combination of new materials design and control of the film structure and device architecture. This perspective outlines the evolution and working principles of SCH OSCs, including proposed mechanisms based on interfacial energetics and spontaneous charge separation. Drawing from recent examples of high-efficiency SCH OSCs, we highlight opportunities for further improvement through molecular engineering, morphology control, and novel device design. Finally, we posit that while SCH OSCs still require substantial materials and device optimisation, they offer a route to simplifying device architectures and provide an insightful lens through which to revisit foundational assumptions in organic photovoltaic device physics.