Interfacial modification in organic solar cells

Organic solar cells (OSCs), consisting of several layers of organic semiconductors stacked between electrodes, have flourished in recent years. However, the energy barrier at the organic semiconductor/electrode interface remains a great challenge, limiting further advancements in device performances. In general, polar and even charged electronically active materials are recognized for their ability to modify the contact between the electrodes and organic semiconductors. Although numerous interlayer materials have been developed, there are still open questions about the mechanisms of interfacial modifications and molecular design strategies. This review focuses on the organic semiconductor/electrode interface in devices, starting with the working mechanism of the interlayers and followed by analyzing various interfacial electronic characteristics, such as the energy level arrangement, based on the basic principles of organic semiconductors. Then, we take the representative interlayer materials as examples and examine their specific working modes and functions in promoting device performance. The combination of mechanistic analysis and case studies provided in this review offer new insights into the development of more efficient organic solar cells for various applications.