Pyrene‐Based Emitter with a Small Energy Gap Between High‐Energy Triplet and Singlet State for High‐Performance Blue Organic Light‐Emitting Diodes
Lei Xu, Yue Yu, Mingke Li, Yulong Li, Wenle Tan, Bohan Wang, Dezhi Yang, Dehua Hu, Lei Ying, Yuguang Ma
Abstract
Abstract Reasonable energy level alignment of molecules is conducive to constructing high‐performance blue emitter. Pyrene is a common building unit in blue emitters with a big energy gap between S 1 and T 1 ( ΔE S1‐T1 ) and small ΔE S1‐Tn (n = 2‐3). By introducing donor and acceptor groups in pyrene, the high‐lying triplet excitons are utilized through reverse intersystem crossing (RISC) channel in obtained blue “hot exciton” emitter CPPCN. Herein, through changing the donor linking type to ortho‐substituted, the obtained derivatives o‐CPPCN exhibited deeper blue emission ( λ max = 448 nm) and a higher k risc (3.1×10 8 s −1 ). The non‐doped device based on o‐CPPCN demonstrates a maximum external quantum efficiency ( EQE max ) of 10.3% with a CIEy of 0.11, along with an exciton utilization of 55%. Photophysical measurements indicate the performance difference between the CPPCN and o‐CPPCN originates from the energy level alignment difference. Compared with CPPCN (0.26 eV), the ΔE S1‐T2 of o‐CPPCN has been reduced to 0.10 eV, proving the smaller gap between T 2 and S 1 state can promote the RISC process. Hence, o‐CPPCN can be employed as the host to prepare “hot exciton” sensitized blue OLED due to its wide band gap and high k risc . The corresponding EQE max of the doped device can be further improved to 11.8%.