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Conjugated polymers are an important class of chromophores for optoelectronic devices. Understanding and controlling their excited state properties, in particular, radiative and non‐radiative recombination processes are among the greatest challenges that must be overcome. We report the synthesis and characterization of a molecularly encapsulated naphthalene diimide‐based polymer, one of the most successfully used motifs, and explore its structural and optical properties. The molecular encapsulation enables a detailed understanding of the effect of interpolymer interactions. We reveal that the non‐encapsulated analogue P(NDI‐2OD‐T) undergoes aggregation enhanced emission; an effect that is suppressed upon encapsulation due to an increasing π‐interchain stacking distance. This suggests that decreasing π‐stacking distances may be an attractive method to enhance the radiative properties of conjugated polymers in contrast to the current paradigm where it is viewed as a source of optical quenching. [ABSTRACT FROM AUTHOR]

This paper demonstrates the use of multiple polyethyleneimine (PEI) films acting as interface layers in the inverted organic light-emitting diodes (OLEDs) to solve the mixing problem between different functional layers. The morphological, electrical and photoluminescence characteristics of PEI films are systematically investigated. The thickness of PEI layers is optimized to achieve both good electron transport and ability of preventing the miscibility. The authors' results show that the insertion of double PEI interface layers in the inverted OLEDs allow the deposition of electron transport layer and emissive layer all in solution. Finally, the authors report an inverted green OLED with one and double PEI interface layers. The green OLED with double PEI interface layers yields a maximum current efficiency of 45.2 cd A-1, which is close to the device using thermal deposition method. The authors thus believe that the application of multiple PEI interface layers could provide a promising way to obtain highly efficient OLEDs in solution processing. [ABSTRACT FROM AUTHOR]

We have systematically investigated hole/electron distribution and exciton dynamics in blue fluorescent and yellow phosphorescent organic light-emitting diodes (OLEDs). We demonstrate that the importance of appropriate charge carrier confinement and exciton management for the realization of highly efficient and stable OLEDs. For yellow phosphorescent device based on Ir(MePQ)2(acac), we have studied the behavior of various intrinsic emission zones on the characteristics of OLEDs with the hole/electron-transporting matrix. The current efficiency increases from 15.7 to 31.7 cd A−1 with the rise in electron-transporting matrix from 20 to 80 nm. We attributed the improved performance to the strong hole-transfer capabilities and relatively weak electron-donating abilities of Ir-complex doped transporting matrix. In contrast, the efficiencies of blue devices decreased with increasing emitting layer (EML), suggesting that the rate of hole-electron pair recombination continuously decrease with the increasing EML thickness due to blue fluorescent dopant hindering hole transfer. In addition, the complementary-color white OLEDs (WOLEDs) with various EML thickness were also demonstrated. Based on their performance, we have found that the use of thin EML in WOLEDs can significantly improve optoelectronic conversion efficiency, whereas deteriorated device properties reversely. [ABSTRACT FROM AUTHOR]

Light extraction efficiency of organic light emitting diode (OLED) was enhanced by attaching a thin film with inverted-pyramid texture onto a glass substrate. Two groups of polyvinyl alcohol (PVA) films with differently shaped inverted-pyramid texture were fabricated by a simple transferring imprint approach, and their effects on light extraction of OLED were studied. We found out that the light extraction was affected mainly by the inclination angle rather than size of inverted-pyramid, which was explained by the classic ray theory as well. Besides, the textured film brought hardly changed emission spectrum and wider viewing angle of the OLED. [ABSTRACT FROM AUTHOR]

We have investigated the photoluminescent characteristics of binaphthyl derivates, 4′′,4′′′- N, N-diphenylamine-4,4′-diphenyl-1,1′-binaphthyl (BN1), 4′′, 4′′′-(9-(9H-9-carbazole)-4, 4′-diphenyl-1, 1′-binaphthyl (BN2) and 4, 4′-bis(9-( p-fluorophenyl)-9H-3-carbazole))-1, 1′-binaphthyl (BN3) and found their amplified spontaneous emission (ASE) from neat films. The ASE threshold of pumping energy, Eth = 4.4, 3.8, 5.3 µJ cm−2 were obtained under optical excitation at 355 nm for the neat films of BNs, 1, 2, and 3, respectively. Moreover, the lasing of those non-doped films exhibited deep-blue emission, whose peak spectra of BNs 1, 2, and 3 were 438, 421, and 428 nm, respectively. We have also studied the thermal-stability of BN1 by annealing at 250 °C for 30 min and found that the ASE threshold stayed almost unchanged compared to untreated film, demonstrating its high heat resistance characteristics. The characteristics of decreased tendency to crystallize and weaker intermolecular interactions in the solid state of BNs make them potential candidates for approaching electrically pumped organic laser diodes. [ABSTRACT FROM AUTHOR]

We have employed the photoluminescent (PL) spectrum of an accelerated aging organic light-emitting diode (OLED) to investigate the mechanisms of molecular decomposition in the whole and each organic functional layer using a bevel-cutting and peel-off method. The devices were operated at a constant current density of 37 mA/cm2 and 70 °C until the luminance reached a half of the initial luminance. The results show a slight or even negligible degradation in PL intensity compared to unbiased devices, indicating that little cracked molecular structure and destroyed host-guest transfer mechanism occurred in organic materials of the biased device Scanning electron microscopy images of devices with bias demonstrated that the delamination at the interfaces of organic layers/Al and light-emitting layer/hole transport layer occurs. We concluded that the charges accumulated at the interface of the heterojunction formed between adjacent organic layers with different energy barriers in or near the emissive layer, as well as the cathode/organic layer, should be mainly responsible for the degradation of OLEDs. [ABSTRACT FROM AUTHOR]

Organic Light-Emitting Diodes Organic light‐emitting diode (OLED) is a potential light source for variable harsh environments ranging from external ornament pasting to fascinating space travel and deep‐sea exploration under high pressure. In article number 2100120, Saihu Pan, Kunping Guo, Bin Wei, and co‐workers study the influence of external pressure on the specific organic functional layer and the whole OLEDs for their electrical and electroluminescence characteristics. It is worth noting that the green fluorescence OLED with a >12% increase in current efficiency by applying pressure of 0.75 MPa for 10 min with respect to the device without pressure treatment. Most interestingly, highly stable OLEDs with long operation lifetime are achieved by specific pressure condition, indicating positive effects of pressure treatment on device stability. Envisioning a bright future, it is reasonable to expect that this study provides a new strategy and insights for material development and high‐performance OLED application under extreme pressure conditions. [ABSTRACT FROM AUTHOR]

Despite considerable interest, uniform and robust flexible transparent conducting electrodes (FTCEs) that can be seamlessly integrated and used for highly efficient large‐area flexible oganic light‐emitting diodes (OLEDs) remain elusive. In this study, a large‐area fabrication of uniform transparent electrodes for high‐performance flexible OLEDs by exploiting the rapid nanowelding process of silver nanowires (AgNWs) onto polyethylene terephthalate substrate under Xe‐lamp irradiation and mechanical pressing treatment is reported. The performance of AgNWs FTCEs is significantly enhanced by applying the Xe‐lamp beam irradiation for 5 s and subsequent compression at 20 MPa for 15 s, achieving a low sheet resistance of 26.5 Ω sq−1, a high transmittance of 95.2% (at 550 nm), and very smooth surfaces with root‐mean‐square of 5.4 nm. Meanwhile, the nanowelded AgNWs FTCEs maintain excellent electrical conductivity (only a 2.96% increase in ΔR/R0) after 1000 bending cycles. The resulting AgNWs FTCEs‐based green phosphorescent OLED achieves an unprecedented external quantum efficiency (EQE) of 23.7% and a current efficiency as high as 81.5 cd A−1. Benefiting from the uniform properties for resulting AgNWs FTCEs, the fabricated flexible OLED with a large area of 25 × 25 mm2 still retains a high EQE of 22.2% and a current efficiency of 78.0 cd A−1. [ABSTRACT FROM AUTHOR]