Realization of Red Iridium-Based Ionic Transition Metal Complex Light-Emitting Electrochemical Cells (iTMC-LECs) by Interface-Induced Color Shift.

Red ionic iridium-based transition metal complex light-emitting electrochemical cells (iTMC-LECs) with emission centered at ca. 650 nm, maximum efficiency of 0.3%, maximum brightness above 650 cd m-2, and device lifetime well above 200 and 33 h at brightness levels of 10 and 210 cd m-2, respectively, are realized by the introduction of a p-type polymer interface to the standard design of [Ir(ppy)2(pbpy)]+[PF6]- (Hppy = 2-phenylpyridine, pbpy = 6-phenyl-2,2'-bipyridine) iTMC-LEC. The unexpected color shift from yellow to red is studied in detail with respect to operation conditions and material combination. The experimental data suggest that either exciplex formation or subordinate, usually suppressed optical transitions of the iTMC might become activated by the introduced interface, causing the pronounced red shift of the peak emission wavelength.

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

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-orange-emitting 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%.

Solution-Processed CuInS2-Based White QD-LEDs with Mixed Active Layer Architecture.

Colloidal quantum dots (QDs) are attractive candidates for future lighting technology. However, in contrast to display applications, the realization of balanced white lighting devices remains conceptually challenging. Here, we demonstrate two-component white light-emitting QD-LEDs with high color rendering indices (CRI) up to 78. The implementation of orange CuInS2/ZnS (CIS/ZnS) QDs with a broad emission and high quantum yield together with blue ZnCdSe/ZnS QDs in a mixed approach allowed white light emission with low blue QD content. The devices reveal only a small color drift in a wide operation voltage range. The correlated color temperature (CCT) could be adjusted between 2200 and 7200 K (from warm white to cold white) by changing the volume ratio between orange and blue QDs (1:0.5 and 1:2).

Quantum Dot/Light-Emitting Electrochemical Cell Hybrid Device and Mechanism of Its Operation.

A new type of light-emitting hybrid device based on colloidal quantum dots (QDs) and an ionic transition metal complex (iTMC) light-emitting electrochemical cell (LEC) is introduced. The developed hybrid devices show light emission from both active layers, which are combined in a stacked geometry. Time-resolved photoluminescence experiments indicate that the emission is controlled by direct charge injection into both the iTMC and the QD layer. The turn-on time (time to reach 1 cd/m(2)) at constant voltage operation is significantly reduced from 8 min in the case of the reference LEC down to subsecond in the case of the hybrid device. Furthermore, luminance and efficiency of the hybrid device are enhanced compared to reference LEC directly after device turn-on by a factor of 400 and 650, respectively. We attribute these improvements to an increased electron injection efficiency into the iTMC directly after device turn-on.

Quantum confinement-controlled exchange coupling in manganese(II)-doped CdSe two-dimensional quantum well nanoribbons.

The impact of quantum confinement on the exchange interaction between charge carriers and magnetic dopants in semiconductor nanomaterials has been controversially discussed for more than a decade. We developed manganese-doped CdSe quantum well nanoribbons with a strong quantum confinement perpendicular to the c-axis, showing distinct heavy hole and light hole resonances up to 300 K. This allows a separate study of the s-d and the p-d exchange interactions all the way up to room temperature. Taking into account the optical selection rules and the statistical distribution of the nanoribbons orientation on the substrate, a remarkable change in particular of the s-d exchange constant with respect to bulk is indicated. Room-temperature studies revealed an unusually high effective g-factor up to ~13 encouraging the implementation of the DMS quantum well nanoribbons for (room temperature) spintronic applications.