Modification of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with sodium-poly(styrenesulfonate) leads to a ca. 0.3 eV increase in the work function and 15 times enhancement in the photoluminescence intensity of the overlying perovskite layer, which is closely correlated with the formation of a highly PSS-enriched top layer. As a direct result, the hybrid halide perovskite light-emitting devices with a modified PEDOT:PSS layer show the maximum external quantum efficiency of 7.2% and power efficiency of 19.0 lm W–1, which are 14–20 times those of the analogous devices using a pristine PEDOT:PSS layer and among the best reported values for the light-emitting devices using a neat perovskite emission layer. Our results illustrate that insufficient hole injection and luminescence quenching at the PEDOT:PSS anode are among the most important factors limiting the external quantum efficiencies of inverted perovskite light-emitting devices.

•Efficient non-doped DMAC-DPS devices with a simple structure.•Efficient monochromatic and white light emitting devices based on DMAC-DPS: TADF materials emission layers.•Contribution of all excitons to light emission in all-TADF devices.We investigate the dependence of the performance of non-doped blue light emitting devices with thermally activated delayed fluorescence (TADF) material bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) emission layer on hole and electron transport layers as well as emission layer thickness and study the underlying device physics. On this basis, efficient green and orange devices using DMAC-DPS as host material and TADF material (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) or 2,3,5,6-tetrakis(3,6-diphenylcarbazol-9-yl)-1,4-dicyanobenzene (4CzTPN-Ph) as emitting dopant are reported. In addition, white devices using single DMAC-DPS: 4CzTPN-Ph emission layer show the maximum external quantum efficiency of 13.4%, maximum power efficiency of 38.3 lm W−1 and current-insensitive Commission Internationale de I'Eclairage (CIE) coordinates of (0.29, 0.39). Compared to the approach of combining TADF host and fluorescent dopant, the present devices enable the utilization of all excitons for light emission and the adoption of broad dopant concentration without significantly affecting device efficiency, which is important for the realization of the desired colour purity for display applications, while maintaining the advantages of simple-structure and low-cost.

Conducting polymer/metal oxide heterostructures have been commonly used in solution-processed tandem organic optoelectronic devices as charge generation layer (CGL) or charge recombination layer. However, the underlying working mechanism remains unexplored. We optimize the preparation of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/zinc oxide (ZnO) CGL and report that the configurations and compositions of the interconnects significantly affect the performance of light-emitting devices. Two-unit and in particular the first reported three-unit solution-processed tandem polymer light-emitting devices show the luminance efficiency matching the total luminance efficiency of the constituent two and three light-emitting units, respectively. Current–voltage and capacitance–voltage measurements on the devices with various interconnects indicate that charges are generated at the PEDOT:PSS/ZnO interface. CGL-generated current can be described with the Richardson–Schottky thermal emission model, yielding the barrier height close to the “effective band gap” of the PEDOT:PSS/ZnO heterostructure.

The morphology and optical and electrical properties of solution-processed and vacuum-deposited 4,4′,4″-tris(carbazol-9-yl)triphenylamine (TCTA):2,2′-(1,3-phenylene)bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole] (OXD-7) composite films are investigated. All of the films exhibit smooth and pinhole-free morphology, while the evaporated films possess enhanced carrier-transport properties compared to solution-processed ones. The close correlation between the carrier-transport feature and the packing density of the film is established. High-efficiency monochromatic and white phosphorescent hybrid organic–inorganic light-emitting diodes with solution-processed small-molecule emissive layers are reported: the maximum external quantum efficiencies of blue, yellow, and red devices are 18.9, 14.6, and 10.2%, respectively; white devices show a maximum luminance efficiency of 40 cd A–1 and a power efficiency of 20.8 lm W–1 at 1000 cd m–2. The efficiencies of blue, red, and white devices represent significant improvement over previously reported values.Keywords: carrier-transport property; hybrid organic−inorganic light-emitting diodes; packing density of the film; solution-processed small-molecule films; vacuum-deposited films

•Enhanced electron injection from ZnO into light emitting polymers by PEIE.•Efficient RGB hybrid organic–inorganic light emitting devices.•Electrophosphorescent devices using solution-processed small molecule emissive layer.We report efficient red, orange, green and blue organic–inorganic light emitting devices using light emitting polymers and polyethylenimine ethoxylated (PEIE) interlayer with the respective luminance efficiency of 1.3, 2.7, 10 and 4.1 cd A−1, which is comparable to that of the analogous conventional devices using a low work-function metal cathode. This is enabled by the enhanced electron injection due to the effective reduction of the ZnO work-function by PEIE, as well as hole/exciton-blocking function of PEIE layer. Due to the benign compatibility between PEIE and the neighboring organic layer, the novel phosphorescent organic–inorganic devices using solution-processed small molecule emissive layer show the maximum luminance efficiency of 87.6 cd A−1 and external quantum efficiency of 20.9% at 1000 cd m−2.Graphical abstractPhosphorescent hybrid organic–inorganic light emitting devices using solution-processed small molecule emissive layer show the maximum luminance efficiency of 87.6 cd A−1, which is among the best reported luminance efficiency values for solution-processed light emitting devices.

•ITO/PEIE as efficient electron injection contact for inverted light emitting devices.•Enhanced luminance efficiency upon addition of a PEIE layer between light emitting polymer and Al.•Efficient electron injection from ITO/PEIE into several light emitting polymers.We report inverted light emitting devices using ethoxylated polyethylenimine (PEIE) as a single electron injection layer for indium tin oxide cathode, which possess comparable efficiency to those using ZnO/PEIE double electron injection layers. Implementation of a PEIE layer between light emitting polymer layer and aluminum has been shown to significantly enhance device efficiency as well. Improvement of device efficiency can be attributed to increased electron injection due to the reduced work function of PEIE modified cathode as well as the hole blocking effect of PEIE layer. Furthermore, PEIE serves as an efficient electron injector for a range of light emitting polymers with wide distribution of energy levels.Graphical abstract

•The relationship of EL property with the morphology, crystallinity and phase purity of PEO: Perovskite film.•Device performance as a function of the compositions of emission layer and Perovskite precursor.•PEO: Perovskite composite light emitting devices with the maximum EQE of ca. 4.0%.The formation of composite layers comprising polymers such as poly(ethylene oxide) (PEO) and organometal halide perovskites (Peros) is an effective way to improve the morphology integrity of Pero films and the performance of Pero light emitting devices. Herein, we report the influences of the ratio of the organic content to inorganic content in the precursors as well as the compositions of PEO: Pero films on their morphology, crystal structure and electroluminescent property. Multilayer Pero light emitting devices show the external quantum efficiency of ca. 4.0% and power efficiency of 7.9 lm W−1.Download high-res image (231KB)Download full-size image