High-Performance, Solution-Processable Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes Realized via the Adjustment of the Composition of the Organoboron Acceptor Monomer in Copolymer Host Materials

Abstract

Organic polymers that exhibit features pertinent to functioning as host materials for thermally activated delayed fluorescence (TADF) emitters have considerable potential in solution-processable organic light-emitting diodes (OLEDs), allowing simple, low-cost, and large-area applications. In particular, polymer hosts have superior characteristics, including facile functionality to introduce various electron donor and acceptor entities, the ability to uniformly disperse and contain small molecular dopants, and the ability to produce more smooth and homogeneous films, compared to those of their small-molecule counterparts. This manuscript describes the design and development of three new styrene-based copolymers (ABP91, ABP73, and ABP55) bearing diphenylacridine as the electron donor and 2,12-di-tert-butyl-7-phenyl-5,9-dioxa-13b-boranaphtho­[3,2,1-de]­anthracene as the electron acceptor. In particular, ABP91, ABP73, and ABP55 were synthesized via variations in the ratio of donor to acceptor monomers to substantiate their influence in OLED applications. With the ability of the styrene backbone of interrupting the direct electronic coupling between the adjacent electron donor and acceptor entities through non-conjugated linkages, high triplet energy can be inherited by the resulting polymers (>2.70 eV). Furthermore, these materials manifest thermal robustness through high decomposition temperatures (between 348 and 366 °C) and high glass transition temperatures (between 234 and 277 °C). Consequently, solution-processable OLEDs fabricated using the newly synthesized copolymers as host materials and the familiar t4CzIPN as a green-emissive TADF dopant deliver state-of-the-art performance with maximum external quantum efficiencies of 21.8, 22.2, and 19.7% for ABP91, ABP73, and ABP55, respectively. To our knowledge, this is, to date, the best performance reported when organic polymers are used as host materials in solution-processable TADF OLEDs. The pragmatic outcomes obtained in this study can provide useful insights into the structure–property relationship to the OLED community for the further development of efficient polymer hosts for use in solution-processable TADF OLEDs.

Benzonitrile-based AIE polymer host with a simple synthesis process for high-efficiency solution-processable green and blue TADF organic light emitting diodes

“…11 External quantum efficiency diagrams of devices (a), and information about the synthesized part (b) with polymers as host materials in recent years. [14][15][16]19,23 the homopolymer P4CzCN-PA-assisted solution-processed OLEDs exhibited a high EQE of 20.9%, which demonstrates the efficient host property of such polymer material. However, after introducing a bulky BCz unit as a copolymer monomer, the efficiency of the devices sharply decreased.…”

“…Thus, beside the above basic requirements, an excellent host for a solutionprocessable device put forward high demands for molecular design, especially the film-forming properties. [14][15][16][17][18][19][20][21] Shao et al reported a series of novel bipolar polymer hosts based on electron-transporting arylphosphine oxide and carbazole units. Based on these polymer hosts, a TADF device with SpiroAC-TRZ, t4CzIPN and TPAPQ as the guest as blue, green and red emitters achieved external quantum efficiencies as high as 15.8%, 17.1% and 10.1%, respectively.…”

Boosting external quantum efficiency to 38.6% of sky-blue delayed fluorescence molecules by optimizing horizontal dipole orientation

“…Because  int is determined by photoluminescence (PL) quantum yield ( PL ), exciton utilization efficiency ( r ), and carrier balance factor (), tremendous efforts have been devoted to exploring luminescent materials with high values in these aspects. Considerable current research interest is focused on purely organic luminescent materials with thermally activated delayed fluorescence (TADF), owing to their excellent theoretical  r values of 100% by virtue of reverse intersystem crossing (RISC) process (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15). The twisted electron donor (D)-acceptor (A) structures of TADF emitters may also bring about bipolar carrier transport ability and thus a high  value.…”

Activating Energy Transfer Tunnels by Tuning Local Electronegativity of Conjugated Polymeric Backbone for High‐Efficiency OLEDs with Low Efficiency Roll‐Off

“…It is worthy to note that the EQE of pBP-PXZ:CBP exhibits no roll-off when the luminance is less than 200 cd m −2 and just 3% decrease at 500 cd m −2 . The EQE can still be maintained above 19% at 1000 cd m −2 , which represents the best efficiency among TADF polymer-based OLEDs so far under high luminance (Figure 6c) [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] . Those results clearly demonstrate that fine-tuning the polymer backbone structure is significant for improving the overall performances of OLEDs.…”