Performance improvements in all-solution processed inverted QLEDs realized by inserting an electron blocking layer

Abstract

Highly efficient, all-solution processed inverted quantum dot light-emitting diodes (QLEDs) are demonstrated by employing 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB) layer as electron blocking layer. Electron injection from ZnO electron transport layer to quantum dots (QDs) emission layer (EML) can be adjusted by thickness of TmPyPB layer, enabling the balanced charge carriers in QDs EML. With optimal thickness of this TmPyPB adjuster, 59.7% increment in the device current efficiency (from 8.2 to 13.1 cd A−1) and 46.2% improvement in the maximum luminance (from 31916 to 46674 cd m−2) are achieved, compared with those of the control QLED which has double hole transport layer structure. On the other hand, we find luminescence quenching process, which often happens at the interface of ZnO nanoparticles and QDs, is not obvious in our QLEDs, in which the ZnO layer is fabricated in precursor method, and this conclusion is verified through Time Resolution Photoluminescence test. In a word, this strategy provides a direction for optimizing charge carrier balance in all-solution processed inverted QLED.

Enhanced Carrier Mobility by Doping NaCl in a Hole-Transport Layer for Electroluminescent Quantum Dots Light-Emitting Diodes

“…Besides reducing the electron transport, increasing the hole mobility of a HTL by introducing a proper doping material is a reasonable option. Previously, it was found that the photoluminescence (PL) properties and stability of QDs were improved after encapsulating QDs in NaCl crystals . In the current study, we investigated the effect of NaCl on atmosphere-process-based EL QLEDs and found that the salt also benefits the carrier mobility of poly­(vinylcarbazole) (PVK), a conductive polymer generally used as an HTL in EL QLEDs, as shown in Figure .…”

“…In general, the mobility of the electron-transport layer (ETL) is higher than that of the hole-transport layer (HTL) in QLED devices, which can cause the carrier imbalance in the QD layer and thus reduce the device performance. There are two possible ways to sort out the problem: (1) the reduction of electron transport by applying an electron blocking layer and (2) the introduction of a high hole mobility additive such as poly­(9,9-dioctylfluorene- alt - N -(4- s -butylphenyl)­diphenylamine) or poly­[bis­(4-phenyl)­(4-butylphenyl)­amine] in a HTL to enhance the hole mobility. For the first method, the hole injection and mobility problems are simply negligible, and the overall carrier mobility of the devices decreases.…”

“…were improved after encapsulating QDs in NaCl crystals. 23 In the current study, we investigated the effect of NaCl on atmosphere-process-based EL QLEDs and found that the salt also benefits the carrier mobility of poly(vinylcarbazole) (PVK), a conductive polymer generally used as an HTL in EL QLEDs, as shown in Figure 1. Because NaCl cannot be directly dissolved with relatively nonpolar PVK in toluene, an appropriate solvent for a mixture of NaCl and PVK is first considered.…”

Effect of Solvent on Optical Properties and Surface Topography of Nanocomposite Conjugated Polymer Thin Film

“…The CP solution is prepared via the solution blending technique. 12 In this technique, the CPs are dissolved in a suitable solvent to reach the homogenous distribution of all the CPs throughout the thin film surface. Different solvents were used to prepare the CP solutions, such as toluene and chloroform.…”