Metal penetration induced interfacial challenges and engineering strategies in OSV devices

Spintronics has emerged as an important research topic in the field of information communication, and organic spin-valve (OSV) devices are fabricated for demonstration and research in this area. Metal penetration of the top ferromagnetic electrodes into organic spacer layers has long been a pervasive challenge in OSV devices. Originating from evaporative deposition and facilitated by the conventional spacer layers, such penetration can severely degrade device performance and even lead to a complete loss of magnetoresistance (MR) signals. In this review, we first summarize the characterization techniques, experimental signatures, physical origins, and effects of metal penetration. Then, we further review diverse strategies developed to suppress metal penetration along the development of spintronics, including interlayer insertion, spacer material selection, electrode preparation and transfer, spacer layer preparation, and junction-area engineering, underscoring their respective advantages and limitations in terms of robustness, reproducibility, purity, and scalability. Finally, we conclude emerging opportunities enabled by metal-organic frameworks (MOFs) as a next-generation spacer material. Owing to their intrinsic properties, MOFs can hierarchically suppress metal penetration via geometric regulation, physical robustness, and local chemical coordination, while preserving clean spin-injection interfaces. We also outlined future research directions towards scalable fabrication and practical implementation of MOF-based spacers, as such optimizations can comprehensively improve the device performance, based on the effective restraint of metal penetration.