Organic light-emitting diodes with ultrastable glass emission layers show increased efficiency and device stability.

Thermally activated delayed fluorescence (TADF)‐type compounds have great potential as emitter molecules in organic light‐emitting diodes, allowing for electrofluorescence with 100% internal quantum efficiency. In small molecules, TADF is achieved through the formation of intramolecular charge‐transfer states. The only design limitation is the requirement that donor and acceptor entities spatially decouple the highest occupied and lowest unoccupied molecular orbitals, respectively, to minimize exchange splitting. The development of polymeric TADF emitters, on the contrary, has seen comparably small progress and those are typically built up from monomeric units that show promising TADF properties in small molecule studies beforehand. By contrast, herein, a way to achieve TADF properties in cyclic oligomers and polymers composed of non‐TADF building blocks is shown. Due to a strongly decreased energy splitting of the polymer with respect to the individual repeating unit between the lowest singlet and triplet excited state (ΔEST) and a sufficiently high radiative decay rate kSr, a highly efficient TADF polymer with up to 71% photoluminescence quantum yield is obtained. For the first time, an encouraging method is provided for producing highly efficient TADF oligomers and polymers from solely non‐TADF units via induced conjugation, opening a new design strategy exclusive for polymers.

easily tunable band gaps. [4][5][6][7] LEDs based on such materials have been attracting increasing attention since the first roomtemperature perovskite LEDs (PeLED) developed in 2014. [13] The development of PeLEDs has progressed very rapidly, realizing a record-high external quantum efficiency (EQE) of 11.7% in 2016. [14] Similar to other LED categories, e.g., organic LEDs (OLEDs) [15] and quantumdot [16,17] LEDs, the EQE of PeLEDs is determined by the internal quantum efficiency (IQE) and light out-coupling efficiency (η), which is expressed asThe IQE is the product of the charge carrier balance (γ), the fraction of excitons capable of radiative decay at room temperature (η S/T ), and the effective radiative quantum yield (q eff ). For 2D perovskite materials with relatively large binding energy, the η S/T could be unity when heavy atoms are involved in the organometallic complex (similar to that in phosphorescent materials [18] ). For 3D perovskite materials with relatively small binding energy, the emission should be bandto-band transitions of free carriers in direct gap semiconductors, and the η S/T term should not be involved in the equation in this case. All in all, this equation shows that the EQE is largely influenced by the η besides the IQE. Thus, studying the limits of η is of great importance for achieving high-EQE PeLEDs.As the fast development of PeLEDs, a conflict appears between the experimental and theoretical results. In general, the η can be estimated according to the ray-optics theory, [19] Light-emitting diodes (LEDs) based on organic-inorganic hybrid perovskites, in particular, 3D and quasi-2D ones, are in the fast development and their external quantum efficiencies (EQEs) have exceeded 10%, making them competitive candidates toward large-area and low-cost light-emitting applications allowing printing techniques. Similar to other LED categories, light out-coupling efficiency is an important parameter determining the EQE of perovskite LEDs (PeLEDs), which, however, is scarcely studied, limiting further efficiency improvement and understanding of PeLEDs. In this work, for the first time, optical energy losses in PeLEDs are investigated through systematic optical simulations, which reveal that the 3D and quasi-2D PeLEDs can achieve theoretically maximum EQEs of ≈25% and ≈20%, respectively, in spite of their high refractive indices. These results are consistent with the reported experimental data. This work presents primary understanding of the optical energy losses in PeLEDs and will spur new developments in the aspects of device engineering and light extraction techniques to boost the EQEs of PeLEDs. Perovskite Light-Emitting DiodesOrganic-inorganic perovskite materials have attracted extensive interest due to their fascinating semiconducting properties, such as high absorption coefficient, long carrier diffusion length, and small exciton binding energy. [1][2][3] Moreover, these materials are easily processed via solution-based techniques, showing great potential applications in low-cost op...

Hyperbranched polyvinylsulfi des have been prepared through a facile, metal-free, radical induced "A 2 +B 3 " thiol-yne polymerization of 1,3,5-tris(naphthalylethynyl) benzene and 1,4-dithiolbenzene with three different input ratios. The resulting polymers exhibit excellent optical properties like high transparency and very high refractive index (RI) of up to 1.7839, combined with high thermal stability ( T d5% up to 420 °C) and excellent solution processability. These properties make them ideal candidates as high RI polymeric materials (HRIP) in connection with light out-coupling schemes for organic light-emitting diodes (OLEDs). A series of hyperbranched HRIPs with varying monomer compositions have been compared in their optical properties. Finally, phosphorescent monochrome OLEDs are fabricated on top of HRIP layers to test the compatibility of HRIPs with state-of-the-art OLEDs. The results show that the HRIPs do not deteriorate the performance of the OLEDs while maintaining external quantum effi ciencies of over 20% for phosphorescent red OLEDs. These results open a pathway toward alternative, low-cost, and scalable out-coupling concepts through refractive index matching of the OLED materials and the HRIPs presented.

White organic light-emitting diodes (OLEDs) are promising candidates for future solid-state lighting applications and backplane illumination in large-area displays. One very specific feature of OLEDs, which is currently gaining momentum, is that they can enable tunable white light emission. This feature is conventionally realized either through the vertical stacking of independent OLEDs emitting different colors or in lateral arrangement of OLEDs. The vertical design is optically difficult to optimize and often results in efficiency compromises between the units. In contrast, the lateral concept introduces severe area losses to dark regions between the subunits, which requires a significantly larger overall device area to achieve equal brightness. Here we demonstrate a color-tunable, two-color OLED device realized by side-by-side alignment of yellow and blue p-i-n OLEDs structured down to 20 μm by a simple and up-scalable orthogonal photolithography technique. This layout eliminates the problems of conventional lateral approaches by utilizing all area for light emission. The corresponding emission of the photo-patterned two-unit OLED can be tuned over a wide range from yellow to white to blue colors. The independent control of the different units allows the desired overall spectrum to be set at any given brightness level. Operated as a white light source, the microstructured OLED reaches a luminous efficacy of 13 lm W−1 at 1000 cd m−2 without an additional light outcoupling enhancement and reaches a color rendering index of 68 when operated near the color point E. Finally, we demonstrate an improved device lifetime by means of size variation of the subunits.