Flexible Crystals, Polymorph Selection and Interface Engineering for Organic Electronics: How New Discoveries and Established Knowledge Can Provide New Stimuli for Research Into Organic Semiconducting Single Crystals

Organic Semiconducting Single Crystals (OSSCs) have long been considered promising materials for organic electronics, due to their high charge carrier mobilities and structural order. However, progress in this field remains limited due to issues such as mechanical fragility, lack of reproducibility of device performance, and difficulties in controlling crystal orientation during integration. Emerging research in three key areas offers new opportunities to overcome these challenges. First, mechanical flexibility, observed in several organic single crystals, is revealing potential for mechanically robust devices. Second, advances in polymorph control, inspired by pharmaceutical crystallography, are enabling more precise control over crystal phase formation. Third, interface engineering, particularly via self-assembled monolayers (SAMs), is proving effective in directing nucleation, polymorph selection, and improving crystal alignment and device performance. Here, the recent progress in these areas is summarized. The structural basis and functional implications of mechanical flexibility in OSSCs are examined, current crystal growth techniques are surveyed, focusing on solution-based methods, and the role of SAMs in tuning interfaces for improved polymorph selection and material performance is evaluated. Remaining bottlenecks hindering large-scale application of OSSCs are identified, and the reviewed topics are proposed as pathways to revitalize OSSC research and accelerate their application in organic electronics.