Highly efficient blue quantum-dot light-emitting diodes based on a mixed composite of a carbazole donor and a triazine acceptor as the hole transport layer

Abstract

Solution-processed thermally activated delayed fluorescence (TADF) exciplexes were employed as hole transport layer (HTL) of blue quantum dot (QD) light-emitting diodes (QLEDs) by blending polymer donors of poly(N-vinylcarbazole) (PVK) with...

Enhanced Performance and High Resistance to Efficiency Degradation of Blue Quantum-Dot Light-Emitting Diodes Using the Lewis Base Blended Hole-Transporting Layers

“…Compared to the neat PVK film, the emission of the blended films exhibits a much narrower and slight red shift in DPPE:PVK films. This indicates a change in the bandgap and the absence of excess heteroemission. ,, The PL peaks of blue QDs on PVK and DPPE:PVK films are identical to the PL peak in the neat blue QDs film, which is observed at 450 nm (as shown in Figure S5b). However, an obvious boost in luminance intensity is observed in blue QDs on films with different ratios of DPPE:PVK.…”

“…For example, blended or double-layered HTLs are commonly employed to promote hole injection. In our group, we have demonstrated that the hole injection can be enhanced by blending the small-molecule receptor, 2,4,6-tris­(biphenyl-3-yl)-1,3,5-triazine (T2T), or blue thermally activated delayed fluorescence (TADF) material, 4,5-bis­(carbazol-9-yl)-1,2-dicyanobenzene (2CzPN), with PVK as HTLs, either by forming exciton complexes or through energy-transfer processes. , A similar strategy was applied by Liu et al, who reported a unique charge injection at the interfaces between HTLs and QDs layer by blending 1,1-bis­[4-[ N , N′ -bis­( p -tolylamino)­phenyl]-cyclohexane] (TAPC) with PVK as HTL . In addition, a double-layered HTL consisting of PVK and poly­[(9,9-dioctylfluorenyl-2,7-diyl)- co -(4,4′-( N -( p -butylphenyl))-diphenylamine)]­(TFB) in blue QLEDs was reported by Cao et al and Chen et al, which reduced the efficiency roll-off, improved the EQE, as well as reduced the turn-on voltage. , …”

High-Throughput Screening of Hole Transport Materials for Quantum Dot Light-Emitting Diodes

“…Further enhancement of the charge carrier mobility within the candidates' films may be achieved via doping and composite engineering. 47 Particular attention should be devoted to the formation of polaron states, which may impact the HOMO level of the HTMs. Given the possibility of charge accumulation at the interface of HTL/ EML, high densities of polaron states may influence the inter-layer energy mismatch and charge transport to the EML, and the overall device performance by, e.g., exciton−polaron quenching.…”

“…These results, along with the low HOMO levels of the candidates, may point to the potential use of the materials for promoting the hole injection into QDs and improving the charge carrier balance within the emitting layers. Further enhancement of the charge carrier mobility within the candidates’ films may be achieved via doping and composite engineering . Particular attention should be devoted to the formation of polaron states, which may impact the HOMO level of the HTMs.…”

“…The imbalance due to excess electrons in the EML may result in charging the QDs, leading to the non-radiative Auger recombination, leakage current to the counter electrode, and materials degradation, a serious bottleneck in the improvement of QLED performance. ,− To avoid these issues, several strategies have been explored by optimizing QLED materials and device structures, such as tuning electron transport and emissive layers as well as applying an insulating layer to reduce the electron flow from the ETL to EML for balancing the carrier injection. ,,,− In parallel to these efforts, a subject of continuing importance and interest for many research groups worldwide is to design and develop novel HTMs with suitable electronic properties that enable better hole transport and injection capability. − …”