Highly Efficient, Low-Roll-Off, Red, “Hot Exciton” Organic Light-Emitting Diodes Promoted by the Heavy-Atom Effect of Selenium

It is important to attain red hot exciton materials applicable in highly efficient organic light-emitting diodes with low-efficiency roll-off, but their development is restricted by the energy gap law. Herein, the sulfur atom was replaced by a heavier selenium atom based on benzothiadiazole to obtain a new benzoselenadiazole acceptor with a heavy atom effect and stronger electron-withdrawing ability. Two novel red hot exciton materials named BSe-DtBuTPA and BSe-2PhCz-d₂₄ were designed and synthesized based on the benzoselenadiazole unit. Benefiting from the heavy-atom effect of selenium and the small ΔE_S1T2, both emitters exhibited ultrafast high-lying reverse intersystem crossing rate constants (7.00 × 10⁷ and 1.17 × 10⁷ s^-1). The devices based on BSe-DtBuTPA and BSe-2PhCz-d₂₄ demonstrated maximum external quantum efficiencies of 4.81 and 7.15% with emission peaks at 653 and 596 nm, respectively. The device based on deep-red BSe-DtBuTPA exhibited negligible efficiency roll-off of 18.5% at 10000 cd/m².