Here, we report efficient and stable indium phosphide (InP) based inverted red quantum dot light-emitting diodes (QLEDs) using a new high mobility and deep HOMO level hole transport layer (HTL) and an optimized sol−gel ZnMgO layer. A new hole transport material, DBTA, containing rigid dibenzothiophene and tertiary amine units has been designed with high hole mobility and a deep HOMO level to inject holes faster into the InP-QDs. Also, to decrease the electron transporting property of the ZnMgO NPs, a sol−gel ZnMgO layer with optimum magnesium content (17%), low-temperature annealing (180 °C), and a selfaging process is used on the transparent electrode. The high mobility DBTA and an optimized sol−gel Zn 0.83 Mg 0.17 O layer with the self-aging process are responsible for achieving good charge balance and suppressing nonradiative losses in InP-QLED. The fabricated QLED with DBTA and optimized sol− gel Zn 0.83 Mg 0.17 O exhibited an external quantum efficiency of 21.8%, current efficiency of 23.4 cd/A, and operating lifetime (LT 50 ) of 1095 h at 1000 cd/m 2 .

Here, we report an efficient inverted red indium phosphide (InP) comprising QD (InP/ZnSe/ZnS, core/shell structure) light-emitting diode (QLED) by modulating an interfacial contact between the electron transport layer and emissive InP-QDs and applying self-aging approach. The red InP-QLED with optimized interfacial contact exhibits a significant improvement in maximum external quantum efficiency and current efficiency from 4.42 to 10.2% and 4.70 to 10.8 cd/A, respectively, after 69 days of self-aging, which is an almost 2.3-fold improvement compared to the fresh device. The analysis indicates the consecutive reduction in electron injection and accumulation in the emissive QD due to changes in the conduction band minimum of ZnMgO (0.1 eV after 10 days of storage) through a downward vacuum-level shift according to the aging times. During the device aging periods, the oxygen vacancy of ZnMgO reduces, which leads to lower the conductivity of ZnMgO. As a result, charge balance of the device is improved with the suppression of exciton quenching at the interface of ZnMgO and InP-QD.

The efficiency and device lifetime of quantum dot light-emitting diodes (QLEDs) devices suffer due to charge unbalance issue resulting from excess electron injection from ZnO electron transport layer (ETL) to...

We report high-efficiency and long-lifetime inverted green cadmium-free (InP-based) quantum dot light-emitting diodes (QLEDs) using a stable ZnO/ZnS cascaded electron transport layer (ETL). We have successfully developed a strategy to spin-coat stable ZnS ETLs with a relatively higher conduction band minimum (CBM) and lower electron mobility than that of ZnO, which leads to balanced carrier injection and an improved device lifetime. Analysis shows that by using the ZnO/ZnS cascaded ETL, electron injection is reduced, resulting in an improved charge balance in the QD layer and suppressed exciton quenching, which preserves the emission properties of QDs. Optimized devices with ZnO/ZnS cascaded ETLs show a maximum external quantum efficiency of 10.8% and a maximum current efficiency of 37.5 cd/A; these efficiency values are an almost 2.2-fold improvement compared to those of reference devices without ZnS. The QLED devices also showed a remarkably long lifetime (LT 70 ) of 265 h at an initial luminance of 1000 cd/m 2 . The predicted half-lifetime (LT 50 ) at 100 cd/m 2 is 60,255 h, which, to our knowledge, is currently the longest lifetime yet reported for InP-based green QLEDs.

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We demonstrate a highly efficient red cadmium-free quantum dot light-emitting diode (QLED) comprising inverted structure and ZnO:Mg nanoparticles as an electron transport layer. Fabricated QLED reveals maximum external quantum efficiency of 4.46% and more than two-fold increase in efficiency (10.17%) after aging for several days. KeywordsCadmium-free quantum dot; light emitting diode; inverted structure; charge balance; electron transport layer.

We report high light extraction from the top emission OLED (TEOLED) device structure by improving mainly the waveguide mode loss in the atomic layer deposition processed thin film encapsulation (TFE) layer. A novel structure incorporating the light extraction concept using evanescent waves and the hermetic encapsulation of a TEOLED device is presented here. When the TEOLED device is fabricated using the TFE layer, a substantial amount of generated light is trapped inside the device due to the difference in refractive index (RI) between the capping layer (CPL) and the aluminum oxide (Al2O3) layer. By inserting a low RI layer at the interface between the CPL and Al2O3, the direction of the internal reflected light is changed by the evanescent waves. The high light extraction with the low RI layer is attributed to the presence of evanescent waves and an electric field in the low RI layer. The novel fabricated TFE structure, CPL/ low RI layer/ Al2O3/ polymer/ Al2O3, is reported here. The current efficiency of the fabricated blue TEOLED device using this low RI layer is improved by about 23% and the blue index value is enhanced by about 26%. This new approach for light extraction will be applicable to future encapsulation technology for flexible optoelectronic devices.