Highly Efficient Nondoped Green Organic Light-Emitting Diodes with Combination of High Photoluminescence and High Exciton Utilization

Abstract

Photoluminescence (PL) efficiency and exciton utilization efficiency are two key parameters to harvest high-efficiency electroluminescence (EL) in organic light-emitting diodes (OLEDs). But it is not easy to simultaneously combine these two characteristics (high PL efficiency and high exciton utilization) into a fluorescent material. In this work, an efficient combination was achieved through two concepts of hybridized local and charge-transfer (CT) state (HLCT) and "hot exciton", in which the former is responsible for high PL efficiency while the latter contributes to high exciton utilization. On the basis of a tiny chemical modification in TPA-BZP, a green-light donor-acceptor molecule, we designed and synthesized CzP-BZP with this efficeient combination of high PL efficiency of η(PL) = 75% in the solid state and maximal exciton utilization efficiency up to 48% (especially, the internal quantum efficiency of η(IQE) = 35% substantially exceed 25% of spin statistics limit) in OLED. The nondoped OLED of CzP-BZP exhibited an excellent performance: a green emission with a CIE coordinate of (0.34, 0.60), a maximum current efficiency of 23.99 cd A(-1), and a maximum external quantum efficiency (EQE, η(EQE)) of 6.95%. This combined HLCT state and "hot exciton" strategy should be a practical way to design next-generation, low-cost, high-efficiency fluorescent OLED materials.

Electron‐Rich Twistacene‐Modified Arylboron Donor–Acceptor Systems: Synthesis, Photophysics, and Electroluminescence with Hot Exciton Response

“…However, the S 2 , T 2 , and T 3 states may generally be converted into S 1 and T 2 states by internal conversion (IC). Thus, compared with a high probability of RISC T 1 →S 1 for other systems, the TADF through T 3 →S 2 and T 2 →S 1 for 4 and T 2 →S 2 and T 2 →S 1 for 5 barely occurs, which can explain the limited EQE in this work.…”

“…Consequently,t he smalle nergy difference (0.05 eV for 4 and 0.20 eV for 5)b etween S 1 and the hot excited state T 2 and other small energy differences among variouse xcited states offer potentialR ISC T 3 or T 2 !S 2 or S 1 processes by TADF.H owever,t he S 2 ,T 2 ,a nd T 3 states mayg enerally be convertedi nto S 1 and T 2 states by internal conversion (IC). Thus, compared with ah igh probability of RISC T 1 !S 1 for other systems, [47][48][49] the TADF through T 3 !S 2 and T 2 !S 1 for 4 and T 2 !S 2 and T 2 !S 1 for 5 barely occurs, which can explain the limited EQE in this work.…”

Crystalline triphenylamine substituted arenes: solid state packing and luminescence properties

“…Design of stable, efficient 1 and robust organic materials 8 as hole transporting, 7a electron transporting 9 and emitter layer 10 are the major challenges in constructing OLEDs. 1, 3,6 Difficulties in the fabrication of multilayer doped OLEDs 11 led to the design of non-doped OLEDs 12 which possess high performance and increased reproducibility over its doped host-guest counterparts. 13 Polyaromatic hydrocarbons (PAH) are efficient luminophores 14 and are best suited as emitters.…”

Promoting Singlet/triplet Exciton Transformation in Organic Optoelectronic Molecules: Role of Excited State Transition Configuration

“…For TADF molecules, exciton transformation happens between S 1 and T 1 34 , while for HLCT and OURTP molecules, the transformation is from the high-lying T n to S m (n > 1 and m ≥ 1) and from S 1 to T n (n > 1), respectively 17, 35 . Principally, all of these transformations require a small Δ E ST .…”