A New Organic Laser Material Design Toward Ultra‐Low Amplified Spontaneous Red Emission and Ultra‐Bright Electroluminescence

Abstract Significant efforts are dedicated to developing new classes of organic semiconductor materials to achieve electrically pumped lasing. However, further advancements are necessary to understand the relationship between the structure and property for the creation of innovative laser materials with high stability, low triplet yield, ultra‐low lasing threshold, and low‐efficiency roll‐off at ultra‐bright electroluminescence. Here, a new design principle is validated for organic semiconductor laser materials, demonstrating simultaneous enhancement in the key figures of merit of low amplified spontaneous emission thresholds ( E th ), efficient electroluminescence, and low triplet yields. By applying the Einstein stimulated emission rate equation and Strickler–Berg approximation, Two red‐emitting laser dimers of Cibalackrot with different linkers are constructed, leading to giant enhancement (≈250%) in oscillator strengths, and stimulated emission cross‐sections. When blended in poly(9,9‐dioctylfluorene‐ alt ‐benzothiadiazole), the new dimers achieve an ultra‐low E th (4.5 ± 0.3 µJ cm −2 ) in the deep red region ( λ ASE = 655 nm), among the lowest reported for deep‐red emitters. Organic light‐emitting diodes (OLEDs) utilizing the dimer blend exhibit low‐efficiency roll‐off under DC mode. Under pulse operation, the OLEDs achieve high current densities (90 A m −2 ) and ultrahigh brightness (≈710 000 cd m −2 ). These findings highlight the dimerization design as an excellent platform to advance organic semiconductor laser materials.