Advantages, challenges and molecular design of different material types used in organic solar cells

The performance of organic solar cells (OSCs) has increased substantially over the past 10 years, owing to the development of various high-performance organic electron–acceptor and electron–donor materials, including polymers, small molecules and fullerenes, used in the photoactive layer. Depending on the combination of donor and acceptor materials, OSCs can be categorized into several types: polymer–fullerene, polymer–small molecule, all-polymer and all-small molecule, as well as multicomponent OSCs in which the photoactive layer comprises three or more photoactive components. This Review provides an overview of the historical development of the different material types used in the photoactive layer of solution-processed OSCs and compares their advantages and limitations. Effective molecular design strategies for each type of OSC are discussed and promising research directions highlighted, particularly those relevant to facilitating the industrial manufacturing of OSCs.