Heavy Chalcogen Elements in OLEDs: Advances of Sulfur and Selenium for Organic Light-Emitting Materials

The rapid development of organic light-emitting diodes (OLEDs) has spurred extensive efforts toward the design of high-performance organic materials. Among various molecular design strategies, the incorporation of heavy chalcogen elements has emerged as an effective approach to regulate excited-state dynamics and enhance device performance. Owing to their unique electronic configurations, tunable oxidation states, and heavy-atom effects, sulfur and selenium play crucial roles in modulating emission properties, strengthening spin-orbit coupling, and promoting exciton utilization of thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) systems. In recent years, significant progress has been made in integrating these elements into diverse emissive frameworks, including donor-acceptor type TADF architectures, multiple-resonance TADF systems, and purely organic RTP materials. Beyond emissive materials, sulfur-containing units have also been explored as components of host materials for phosphorescent OLEDs. This review provides a comprehensive overview of recent advances in these sulfur- and selenium-based purely organic materials for OLED applications, highlighting the crucial role of chalcogen-incorporated molecular design strategies in advancing OLED technology.