Efficient quantum dot light-emitting diodes with ultra-homogeneous and highly ordered quantum dot monolayer

Abstract

Regarding conventional quantum dot lightemitting diodes (QLEDs) fabricated by using the spin-coating (SC) technique, voids and interstitial spaces are inevitable due to unordered quantum dots (QDs) stacking, generating device leakage current under an external bias. In the present study, we fabricated an ultra-homogeneous and highly ordered QD monolayer by adopting the Langmuir-Blodgett (LB) technique. The QD monolayer was transferred as a emissive layer with a horizontal lifting (HL) method to a red QLED, which exhibited high performance with an external quantum efficiency (EQE) of 19.0% and lifetime (T 95 @100 cd m −2 ) of 13,324 h. When compared with the SC-based device, the EQE and lifetime were improved by 15% and 183% due to the compact and ordered QD monolayer that lowered the leakage current. Moreover, white QLEDs with stacked QD monolayers could be obtained at a low voltage of 4 V because LB technique is an organic-solvent-free approach avoiding interlayer mixing and controlling the QD layer thickness precisely. In addition, we successfully fabricated an ultra-homogeneous large-area QD monolayer on a rectangular substrate with a size of 9 cm × 5 cm, indicating the promising size scalability of the LB-HL strategy.

Integration of ternary I-III-VI quantum dots in light-emitting diodes

“…The spin-coating method consists of diluting TQDs in a solvent, and this solution is dispersed on the surface of the layer where TQDs will be deposited. Subsequently, the wafer is rotated using centrifugal force until the solvent is evaporated and the film is deposited ( Zhao et al, 2021 ). The layer thickness of the obtained TQDs is in the nanometric or micrometric scale, although a lower thickness increases the efficiency and brightness of the LED.…”

Perovskite Quantum Dot Light-Emitting Memcapacitor

“…Perovskite quantum dots (PQDs) have garnered great interest in the field of light-emitting diodes (LEDs) due to their unique photoelectric characteristics, such as high photoluminescence quantum yield (PLQY), adjustable emission wavelength, and high color purity. − In the past few years, with the in-depth study of perovskite material design and device optimization, the external quantum efficiencies (EQEs) of PQD-based LEDs (PQLEDs) have been greatly improved. − However, due to the insufficient understanding of the operating mechanisms of PQLEDs, the device performance of PQLEDs − is still far behind that of organic LEDs − and Cd-based quantum dot LEDs. − In particular, due to the structural instability of PQDs, ion migration is prone to occur in the device, resulting in the degradation of external quantum efficiency. − As we all know, when two semiconductors come in contact, contact potentials are formed on both sides of the contact interface due to differences in work functions. , In PQLEDs, the contact potential generated at the device interface may cause ions in the PQD film to move to both sides of the device, creating a large number of defects. These defects can not only lead to the formation of nonradiative recombination centers but also seriously affect carrier injection and transmission, thereby degrading the device performance.…”

All Solution‐Processed High Performance Pure‐Blue Perovskite Quantum‐Dot Light‐Emitting Diodes

“…The performance of LEDs is affected not only by the luminous efficiency of emission layer but also by the balance of charge injection. [34][35][36] It is well-known that the electron mobility of the ZnO ETL is much faster than the hole mobility of the organic HTL, which easily causes the unbalanced charge injection within the PeLEDs. The I-V test was carried out to analyze the effect of the introduced ligand in colloidal ZnO solution on the conductivity of the ZnO film.…”