All‐Fluorescence White Organic Light‐Emitting Diodes Exceeding 20% EQEs by Rational Manipulation of Singlet and Triplet Excitons

Abstract White organic light‐emitting diodes (WOLEDs) composed of conventional fluorophores possess color purity, low efficiency roll‐off, and rare metal absence, but suffer from theoretical limits due to the lack of triplet utilization. Due to the different diffusion distance for singlets and triplets, multiple Förster resonance energy transfer (FRET) channels can be adequately built up. Herein, besides the complementary component, a blue fluorescence layer, hosted by pure hydrocarbon material SF4‐TPE, is put forward as the spatial exciton manipulating layer to rationally allocate singlets and triplets to the corresponding channels. Hence, singlets are captured by the blue fluorophore, diffused triplets subsequently undergo energy resonance between the blue fluorophore and green assistant, and up‐conversion effect for eventual emission from the yellow fluorophore. Owing to the utilization of singlets and triplets, all‐fluorescence WOLEDs exhibit high efficiency exceeding 20%, with slight efficiency roll‐off even under high luminance of 5000 cd cm⁻². Moreover, CIE coordinates can be surrounding and precisely inside the American National Standard Institute (ANSI) quadrangles, as well as outstanding color stability (ΔCIE‐(x, y) within (0.001, 0.012)) from 300 to 13000 cd cm⁻².