Abstract
In the past two decades, bulk heterojunction organic photovoltaic (OPV) devices have emerged as attractive candidates for solarenergy conversion due to their lightweight design and potential for low-cost, high-throughput, solution-phase processability.Interfacial engineering is a proven efficient approach to achieve OPV devices with high power conversion efficiencies. Thismini-review provides an overview of the key structural considerations necessary when undertaking the molecular design ofconjugated polyelectrolytes, for application as interfacial layers (ILs). The different roles of ILs are outlined, together with theadvantages and disadvantages of competing classes of IL materials. Particular emphasis is placed on the design and synthesisof water-soluble polythiophene-based ILmaterials and the influence of their structural characteristics on their performance asa promising class of ILmaterial. Finally, the challenges and opportunities for polythiophenes as ILmaterials forOPV devices andother solution-processed solar cell technologies (e.g. perovskite solar cells) are discussed.