Large‐area, ultrathin light‐emitting devices currently inspire architects and interior and automotive designers all over the world. Light‐emitting electrochemical cells (LECs) and quantum dot light‐emitting diodes (QD‐LEDs) belong to the most promising next‐generation device concepts for future flexible and large‐area lighting technologies. Both concepts incorporate solution‐based fabrication techniques, which makes them attractive for low cost applications based on, for example, roll‐to‐roll fabrication or inkjet printing. However, both concepts have unique benefits that justify their appeal. LECs comprise ionic species in the active layer, which leads to the omission of additional organic charge injection and transport layers and reactive cathode materials, thus LECs impress with their simple device architecture. QD‐LEDs impress with purity and opulence of available colors: colloidal quantum dots (QDs) are semiconducting nanocrystals that show high yield light emission, which can be easily tuned over the whole visible spectrum by material composition and size. Emerging technologies that unite the potential of both concepts (LEC and QD‐LED) are covered, either by extending a typical LEC architecture with additional QDs, or by replacing the entire organic LEC emitter with QDs or perovskite nanocrystals, still keeping the easy LEC setup featured by the incorporation of mobile ions.

Light‐emitting electrochemical cells (LECs) are solution processable solid‐state light sources comprising in their simplest architecture an ionic emissive layer in between of two electrodes. Although LECs possess several advantages that make them promising candidates for future large‐area low‐cost lighting technologies, their device wall‐plug efficacies remain so far moderate on the order of a few lumens per watt. One of the reasons therefore is considered to be the charge imbalance within the device. Here, a hybrid LEC device concept is introduced, whereby an additional layer of zinc oxide (ZnO) nanoparticles at the cathode side supports electron injection into the active light‐emitting layer and boosts the performance of the Ir‐based ionic transition metal complex LEC (iTMC‐LEC). The brightness and efficacy of the devices can be increased in average by more than 70% by the implementation of the additional inorganic layer. The time to reach the maximum brightness can be reduced in average by a factor of 7, which is attributed to an improved electron/hole balance in the device due to enhanced electron injection into the active iTMC layer.

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.

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)] + [PF 6 ] − (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.

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 CuInS/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).