Look beyond the surface: recent progress in applications of surface-segregated monolayers for organic electronics

Structural control of organic semiconductor thin films at the interface and in the bulk is vital for their use in various organic electronic devices. In this focus review, we provide an overview of the formation and functions of surface-segregated monolayers (SSMs) on organic semiconductor films. Driven by the low surface energy of the molecules, SSMs are spontaneously formed through molecular self-organization during spin-coating from solution. Careful design of SSM molecules allows the formation of highly ordered surface monolayers with high coverage densities. SSMs can be used to induce changes in the molecular structure and the orientation in the bulk film, which can be exploited to improve the bulk properties of films. Film surfaces covered with SSMs can be used to change the interfacial properties of organic/metal and organic/organic interfaces in various organic electronic devices. These modifications can drastically alter the performance of devices, demonstrating the general importance of interfaces. We conclude the review by discussing directions for further development of SSMs and applications in the field of organic electronic devices.