Design and Realization of White Quantum Dot Light-Emitting Electrochemical Cell Hybrid Devices

Abstract

The simple device architecture as well as the solution-based processing makes light-emitting electrochemical cells (LECs) a promising device concept for large-area flexible lighting solutions. The lack of deep-blue emitters, which are, at the same time, efficient, bright, and long-term stable, complementary to the wide variety of yellow-orangeemitting LECs, hampers the creation of white LECs. We present a hybrid device concept for the realization of white light emission by combining blue colloidal quantum dots (QDs) and an Ir-based ionic transition-metal complex (iTMC) LEC in a new type of white QD−LEC hybrid device (QLEC). By careful arrangement of the active layers, we yield light emission from both the blue QDs and the yellow iTMC emitter already at voltages below 3 V. The QLEC devices show homogeneous white light emission with high color rendering index (up to 80), luminance levels above 850 cd m −2 , and a maximum external quantum efficiency greater than 0.2%.

Hybrid White‐Light‐Emitting Electrochemical Cells Based on a Blue Cationic Iridium(III) Complex and Red Quantum Dots

“…The previously reported hybrid white LEC based on a yellow iTMC and blue QDs also suffered a high hole‐injection barrier at the poly( N ‐vinylcarbazole)/blue QDs interface (1.1 eV) and the peak EQE (ca. 0.2 %) was limited as well [33] . These results confirm that improving carrier injection for QD emissive layer to optimize carrier balance is a key to achieving highly efficient hybrid white LECs based on iTMC/QDs emissive bilayers.…”

“…The color rendering index (CRI) of the white EL spectrum at 5–8 V ranges from 64 to 84 (Table 1). The previously reported hybrid white LEC based on a yellow iTMC and blue QDs also showed more intense blue EL from QDs on increasing the bias voltage [33] . Compared with the emissive layer of iTMC containing in situ conductive dopant, which reduces the resistance significantly, [48] the QD emissive layer is less conductive, and thus the increased bias voltage mostly drops across the QD emissive layer, with more QD emission at higher bias.…”

“…However, most high‐efficiency iTMCs are blue, [22–24] green, [19, 20] and yellow, [25] whereas the reported red iTMCs commonly show lower photoluminescence quantum yields, [26–29] which limit further enhancement of the device efficiency of host–guest white LECs based on iTMCs. Recently, incorporation of efficient QDs in LECs [30–32] has inspired the idea of the hybrid white LECs combining a yellow iTMC and blue QDs [33] . However, the reported external quantum efficiency (EQE) of this hybrid white LEC is moderate (ca.…”

Light‐Emitting Electrochemical Cells with Polymer‐Blended InP/ZnSeS Quantum Dot Active Layer

“…In addition, PEDOT:PSS also serves as the hole injection layer (HIL) for QD‐LECs, as is known from previous studies. [ 22,23,29 ] The entire device fabrication process is performed inside an inert glovebox filled with nitrogen. By exploiting the vertical phase separation between the QD layer and PVK layer the two critical layers of the device could be formed from a single film‐casting step, which allows simplifying the device fabrication.…”

“…Even though the simplicity of the LEC structure and the excellent optical properties of QDs have been validated separately, only a limited number of studies have been conducted on the use of QDs as the emissive materials of LECs, [ 22–25,29 ] and the resulting performance of the device, e.g., the luminescence efficiency or the maximum luminescence, requires further improvement to ensure practical utility of these devices. This is perhaps because of the challenges in introducing a balanced number of electrons and holes from the simple device structure into the QDs.…”