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Organic light-emitting diode (OLED) is an electroluminescent technology that relies on charge-carrier dynamics and is a potential light source for variable environmental conditions. Here, by exploiting a self-developed low-temperature testing system, we investigated the characteristics of hole/electron transport, electro-optic conversion efficiency, and operation lifetime of OLEDs at low-temperature ranging from –40 °C to 0 °C and room temperature (25 °C). Compared to devices operating at room temperature, the carrier transport capability is significantly decreased with reducing temperature, and especially the mobility of the hole-transporting material (HTM) and electron-transporting material (ETM) at –40 °C decreases from 1.16 × 10−6 cm2/V⋅s and 2.60 × 10−4 cm2/V⋅s to 6.91 × 10−9 cm2/V⋅s and 1.44 × 10−5 cm2/V⋅s, respectively. Indeed, the temperature affects differently on the mobilities of HTM and ETM, which favors unbalanced charge-carrier transport and recombination in OLEDs, thereby leading to the maximum current efficiency decreased from 6.46 cd⋅A−1 at 25 °C to 2.74 cd⋅A−1 at –40 °C. In addition, blue fluorescent OLED at –20 °C has an above 56% lifetime improvement (time to 80% of the initial luminance) over the reference device at room temperature, which is attributed to efficiently dissipating heat generated inside the device by the low-temperature environment. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials have continued to attract interest due to their rapid improvements in efficiency, non-toxic and potential to be manufactured at energy-saving organic light-emitting diode for full-color display and solid-state lighting. Here, The bipolar and electroluminescence (EL) characteristics of TADF host, 11-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-12,12-dimethyl-11,12-dihydroindeno[2,1- a ]carbazole (DPDDC), were investigated. By incorporating the phosphorescent tris[2-(p -tolyl)pyridine]iridium(III) [Ir(mppy) 3 ] dopant into the matrix, DPDDC showed more excellent EL performance compared with the typical 4,4′-bis(N -carbazolyl)-1,1′-biphenyl (CBP) host. The turn-on voltage for phosphorescent organic light-emitting diodes (PhOLEDs) was decreased to 2.2 V from 2.5 V by exploiting the TADF host instead of CBP. Crucially, we found that the ratio of Ir(mppy) 3 in TADF host plays a significant role in EL process. Remarkable low efficiency roll-off was achieved with above 90% of the current efficiency maintained even at a brightness of 3000 cd m−2, along with high power efficiency of 84.8 lm·W−1 and the external quantum efficiency of 20.6% for DPDDC: 5 wt% Ir(mppy) 3 -based device. Phosphorescent organic light-emitting diodes with low extremely turn-on voltage and high power efficiency by incorporating phosphorescent tris[2-(p -tolyl)pyridine]iridium(III) [Ir(mpppy) 3 ] dopant into TADF host. [Display omitted] • TADF host with bipolar (electron/hole) transport characteristics and excellent electroluminescence performance were investigated. • Turn-on voltage of green PhOLED as low as 2.2 V by exploiting TADF host. • State-of-the art PhOLED exhibited high power efficiency of 84.8 lm·W−1, maximum EQE of 20.6% and efficiency roll-off of 6% at 1000 cd m−2. [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]

Solution-processed perovskite light-emitting diodes (PeLEDs) show great potential for low-cost fabrication of large-area display panel, however, large crystallinity and poor film coverage generally cause high operating voltage and low luminescence efficiency in all solution-processed PeLEDs, and thus limiting their commercial applications. Here, the phenylpropylammonium bromide (PPABr) as ligand additive in MAPbBr 3 for improving perovskite film quality and the device performance of PeLEDs are reported. With varying additive ratios of PPABr, the morphological changes and photoluminescence properties of perovskite film were investigated. Benefiting from precisely managing the ratio, the PPABr-based perovskite films exhibited well-defined crystal phase and high photoluminescence intensity. As a result, all solution-processed MAPbBr 3 PeLEDs with the optimized concentration of PPABr showed a low turn-on voltage of 2.2 V and a maximum device luminance of 13,666 cd/m2, which are comparable to the non-additive device (with turn-on voltage and luminance of 3.0 V and 2910 cd/m2). Notably, an approximately 5.5-fold improvement for 0.09 mol PPABr-based device in current efficiency was achieved compared to the pristine MAPbBr 3 PeLED. High performance all solution-processed perovskite light-emitting diodes by incorporating long ligand the phenylpropylammonium bromide as additives into MAPbBr3 layer. [Display omitted] • High performance all solution-processed PeLEDs were designed and fabricated. • PPABr as additives for MAPbBr 3 significantly enhance the crystalline phase and PL properties of thin film. • State-of-the-art MAPbBr 3 PeLEDs exhibited ultra-low turn-on voltage of 2.2 V. • An approximately 5.5-fold improvement in current efficiency was achieved for the PPABr-based device. [ABSTRACT FROM AUTHOR]

Inverted organic light-emitting diodes (IOLEDs) have great potential application in flat-panel display. In this study, a lithium (Li) ion doped solution processed zinc oxide (Li-ZnO) layer was employed as the cathode buffer layer (CBL) for IOLEDs. The Li-ZnO CBL was prepared by inducing the Li ion of 8-hydroxyquinolatolithium (Liq) to diffuse into ZnO film through thermal annealing the bi-layer ZnO/Liq film. Based on the Li-ZnO CBL with ultraviolet(UV) treatment, the IOLED using tris(8-hydroxyquinoline) aluminum as the emitting layer possessed an optimal current efficiency of 4.42 cd A−1, which was improved by 55% than those of the devices with neat ZnO as CBL. The enhancement of the device performance could be attributed to the enhanced electron mobility and electron injection ability of the Li-ZnO CBL. Our finding indicates that the low-temperature deposited Li-ZnO film has great potential for the application of OLED display. [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]