Bifunctional Electron-Transporting Agent for Red Colloidal Quantum Dot Light-Emitting Diodes

Abstract

Indium phosphide (InP) quantum dots have enabled light-emitting diodes (LEDs) that are heavy-metal-free, narrow in emission linewidth, and physically flexible. However, ZnO/ZnMgO, the electron-transporting layer (ETL) in high-performance red InP/ ZnSe/ZnS LEDs, suffers from high defect densities, quenches luminescence when deposited on InP, and induces performance degradation that arises due to trap migration from the ETL to the InP emitting layer. We posited that the formation of Zn 2+ traps on the outer ZnS shell, combined with sulfur and oxygen vacancy migration between ZnO/ZnMgO and InP, may account for this issue. We synthesized therefore a bifunctional ETL (CNT2T, 3′,3′″,3′″″-(1,3,5triazine-2,4,6-triyl)tris(([1,1′-biphenyl]-3-carbonitrile)) designed to passivate Zn 2+ traps locally and in situ and to prevent vacancy migration between layers: the backbone of the small molecule ETL contains a triazine electron-withdrawing unit to ensure sufficient electron mobility (6 × 10 −4 cm 2 V −1 s −1 ), and the star-shaped structure with multiple cyano groups provides effective passivation of the ZnS surface. We report as a result red InP LEDs having an EQE of 15% and a luminance of over 12,000 cd m −2 ; this represents a record among organic-ETL-based red InP LEDs.

Interfacial Passivation Engineering for Highly Efficient Quantum Dot Light-Emitting Diodes via Aromatic Amine-Functionalized Dipole Molecules

“…Panels b and c of Figure illustrate the adsorption energy ( E ads ) and defect passivation between the QD and dipole molecules. The previous reports showed that zinc vacancies (V Zn ) and sulfur vacancies (V S ) have lower defect formation energy than sulfur interstitials (S int ), and zinc interstitials (Zn int ), which are two dominant defects in ZnS, indicating S atoms and Zn atoms are exposed on the (111) ZnS surface. , The X-ray diffraction (XRD) plots of QD in Figure S3 confirmed the shell of QD is consistent with a zinc blende structure of ZnS Figure S4 illustrates E ads of QD and OA ligands.…”

Impact of Alternating-Current Operation on All-Inorganic Quantum Dot Light-Emitting Diodes

“…To alleviate this issue, we introduce pentafluoro­benzenethiol (PF-BT) at the interface between NiO and the QDs to facilitate the hole injection. This molecule serves as a dipole layer, effectively downshifting the VBE of the NiO film by 0.25 eV, accompanied by the passivation of nonstoichiometric Ni states (Ni 3+ ). − Consequently, the QD-LED now exhibits an enhanced peak current efficiency of 1.7 cd/A (Figure S2).…”

Advancements in semiconductor quantum dots: expanding frontiers in optoelectronics, analytical sensing, biomedicine, and catalysis

“…The bifunctional ETL successfully passivated Zn 2+ traps and prevented migration between layers, leading to a 1.4-fold EQE improvement compared to traditional ZnMgO controls. 104 Minh-Son Hoang et al addressed phase separation in a hybrid poly(9,9-dioctylfluorene- alt-N -(4-sec-butylphenyl)-diphenylamine) (TFB) and polyvinylcarbazole (PVK) system used as a HTL for QLEDs. Without phase separation, the hybrid HTL significantly improved QLED performance, reducing turn-on voltage by approximately 47% and increasing brightness by around 37%.…”