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The emitter 9,9′,9′'‐(5‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)benzene‐1,2,3‐triyl)tris(9H‐carbazole) (3CzTRZ) seems an ideal candidate for efficient single‐layer blue organic light‐emitting diodes (OLEDs). It combines trap‐free electron and hole transport with thermally activated delayed fluorescence (TADF) for triplet harvesting. However, in spite of the absence of charge trapping defects, neat films of 3CzTRZ suffer from a low photoluminescence quantum yield (PLQY) of only 40%. Time‐resolved photoluminescence measurements reveal that the low PLQY results from the fact that next to fast intersystem crossing the rate for reverse intersystem crossing is very slow and nearly similar to the rate of non‐radiative recombination of triplet excitons to the ground state. This loss process of non‐radiative triplet decay is even more pronounced in OLEDs due to the 75% direct triplet‐exciton formation, resulting in a low external quantum efficiency (EQE) of 4.5%. By diluting 3CzTRZ in a large bandgap host, the triplet lifetime is increased by at least an order of magnitude, resulting in an enhanced PLQY of 70% and a more than three‐fold enhancement of the EQE to 15% in a single‐layer blue OLED. Device simulations confirm that the increased EQE can be ascribed to an elongated triplet lifetime upon dilution of the emitter in a host matrix. [ABSTRACT FROM AUTHOR]

For single‐layer OLEDs to achieve efficiencies approaching those of multilayer devices, balanced charge transport is a prerequisite. We demonstrate a single‐layer blue‐emitting OLED with unity internal quantum efficiency and an external quantum efficiency of 27.7% with minor roll‐off at high brightness. These findings lay the foundations for efficient solution‐processed OLEDs. [ABSTRACT FROM AUTHOR]

The efficiency and stability of single‐layer polymer light‐emitting diodes is compromised by unbalanced charge transport, absence of triplet‐exciton harvesting and low photoluminescence quantum efficiencies. We demonstrate that tuning the energy levels of the organic semiconductor can prevent charge trapping, which is the main cause of unbalanced charge transport. By additionally using a novel strategy to enhance charge injection, efficient single‐layer organic light‐emitting diodes are presented based on a trap‐free organic semiconductor exhibiting thermally activated delayed fluorescence. [ABSTRACT FROM AUTHOR]

Highlights: [•] We present a highly effective method of preventing short circuits in OLEDs. [•] The method also proved highly effective in reducing leakage currents. [•] The treatment has little to no effect on the luminance of the OLED devices. [•] The treatment has no detrimental effect on the lifetime of the OLED devices. [•] We deem the repair method to be compatible with large scale production of OLEDs. [Copyright &y& Elsevier]

A method is presented to self-repair cracks in embedded silver grid structures used in large area organic electronics. The repair procedure is based on electro-deposition, incited by the application of a moderate DC voltage across the crack. During this process the organic anode that is in direct electrical contact with the silver grid, functions as an appropriate medium for ion migration. Restoration of conductivity is achieved by the formation of dendritic metal structures that connect the cathodic to the anodic side of the crack. The metal dendrites decrease the gap resistance by one order of magnitude. Subsequently, another three orders of magnitude are gained upon sintering the dendrites using a high voltage pulse, yielding restored conductance levels nearly within one order of magnitude difference from native track conductance. [ABSTRACT FROM AUTHOR]