To reduce cost and improve environmental sustainability, there continues to be an important need for the development of efficient organic light‐emitting diodes (OLEDs) that do not rely on heavy metal‐containing compounds. In particular, the efficiency of fluorescent near‐infrared (NIR) OLEDs continues to lag well‐behind that of their platinum‐containing counterparts. Low efficiencies in this spectral range mainly arise from the low quantum yields of fluorescent NIR emitters due to the energy gap law and inefficient harvesting of triplet excitons. In this paper, a thermally activated delayed fluorescent (TADF) material is used as the assistant dopant to demonstrate pure NIR‐emitting fluorescent OLEDs with an external quantum efficiency of up to 3.8%, with an electroluminescence maximum at 840 nm and a spectral full‐width at half‐maximum of < 40 nm. The efficiency is more than three times higher than that of the best previously reported fluorescent OLEDs in this spectral range and approaches that achievable with the best platinum‐containing phosphorescent emitters.

International audienceWe report on the near infrared electroluminescence properties of a Nd3+ complex with thenoyltrifluoroacetone and 1,10-phenantroline ligands in solution-processed organic light-emitting diodes. Spin-coated blends containing a 1,3-bis(9-carbazolyl)benzene host doped with the Nd3+ complex were found to exhibit a photoluminescence quantum yield of about 0.5%, regardless of the doping concentration level. Electroluminescent devices based on these small molecule blends showed the characteristic emission of Nd3+ at 890, 1060 and 1330 nm with an external quantum efficiency as high as 0.022%. These improved performances were mainly attributed to direct charge trapping and exciton formation on the near infrared emitter. Importantly, the efficiency roll-off at high current densities due to triplet-triplet exciton annihilation in the device containing 20 wt% of the complex was lower than what is typically observed in lanthanide complex-based electroluminescent devices. This is presumably due to the high triplet energy of the host material, which prevents guest-to-host energy-back transfer and thus host-guest triplet-triplet exciton annihilation

Recent improvements in efficiency and luminance of quantum-dot light-emitting diodes (QLEDs) promise a versatile technology for next-generation lighting and display applications. This is accomplished due to the advances in colloidal quantum-dot (CQD) synthetic methods together with proper engineering of the charge balance in these devices. The exciton quenching mechanisms occurring at the interface between the QD emissive layer and the zinc oxide (ZnO) electron transport layer (ETL) are one of the important parts of the charge transport path, affecting efficiency and long-term stability. Herein, a comprehensive overview of the advances in the engineering of ZnO-based ETLs, in terms of device efficiency and operational stability, is attempted. It is specifically highlighted that significant improvements can be achieved using various ZnO ETL defect passivation methods. This review also describes the key requirements for high-performance QLEDs from the ETL engineering aspect and catalyzes for further interdisciplinary explorations to realize reliable devices for practical applications.

We report the enhanced near-infrared (NIR) electroluminescence from a Nd 3+ -complex with thenoyltrifluoroacetone and 1,10phenanthroline ligands. The NIR-emitting complex was blended into an exciplex-forming co-host system comprising 2,7bis(diphenylphosphoryl)-9,9'-spirobifluorene as the electron transport material and 4,4',4"-tris(carbazol-9-yl)triphenylamine as the hole transport material, in solution-processed small molecule organic light-emitting diodes (OLEDs). This binary ambipolar host system favors direct charge trapping and exciton formation on the Nd 3+ -complex molecules. Efficient energy transfer from the singlet and triplet exciplexes formed between the host molecules to the Nd 3+ ions contributes to the enhanced luminescence efficiency. The photoluminescence quantum yield of this blend is 1.2%, and the optimized OLED shows a maximum electroluminescence external quantum efficiency of 0.034%. The device also exhibits a low efficiency roll-off of only 12% over a current density range of 100 mA/cm 2 , due to the reduced triplet-polaron annihilation.

The synthesis, characterization, photophysical and redox properties of a dinuclear complex Zn 2 (AMOX) 4 (AMOX = 4-bromo-N,N′-diphenylbenzamidinate N-oxide) are highlighted. This compound is a first example of a novel class of aggregation-induced emission (AIE) materials. Noticeably, solution-processed white-green organic light-emitting diodes were fabricated using this complex as dopant in a co-host matrix in the [a] 4324 gands. This distinction indicates that the energy of the LUMO can be fine-tuned by modifying the C-aryl substituents with EW/ED groups. The TD-DFT calculations for 1 ( Figure S10, Table Eur.

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In this study, we perform a simulation analysis to investigate the influence of p-type and n-type doping concentration in BHJ SCs using the drift-diffusion model. Specifically, we investigate the effect of doping on the charge carrier transport and calculate the above-mentioned device parameters. We show that doping the active layer can increase the cell characteristic parameters, that the results are in an excellent agreement with the experimental results previously reported in the literature. We also show that doping causes space charge effects which subsequently lead to redistribution of the internal electric field in the device. Our results reveal that higher doping levels lead to screening the electrical field in the P3HT:PCBM active region. This in turn forces the charge carrier transport to be solely dominated by the diffusion, consequently decreasing the performance of the device. We also show that doping of the active layer to an optimum level can effectively improve the charge transport. Moreover, we show that doping can create an Ohmic contact between the organic and cathode interface. Additionally, the charge carrier concentration profile shows that by increasing the dopant concentration, the $$J_{sc}$$ J sc can be improved remarkably. Upon doping the active layer, this indicates that illumination can simply reduce the series resistance in the device.

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