Organic light emitting diodes (OLEDs) have been well known for their potential usage in the lighting and display industry. The device efficiency and lifetime have improved considerably in the last three decades. However, for commercial applications, operational lifetime still lies as one of the looming challenges. In this review paper, an in-depth description of the various factors which affect OLED lifetime, and the related solutions is attempted to be consolidated. Notably, all the known intrinsic and extrinsic degradation phenomena and failure mechanisms, which include the presence of dark spot, high heat during device operation, substrate fracture, downgrading luminance, moisture attack, oxidation, corrosion, electron induced migrations, photochemical degradation, electrochemical degradation, electric breakdown, thermomechanical failures, thermal breakdown/degradation, and presence of impurities within the materials and evaporator chamber are reviewed. Light is also shed on the materials and device structures which are developed in order to obtain along with developed materials and device structures to obtain stable devices. It is believed that the theme of this report, summarizing the knowledge of mechanisms allied with OLED degradation, would be contributory in developing better-quality OLED materials and, accordingly, longer lifespan devices.
A new type of ruthenium complexes 6–8 with tridentate bipyridine–pyrazolate ancillary ligands has been synthesized in an attempt to elongate the π‐conjugated system as well as to increase the optical extinction coefficient, possible dye uptake on TiO2, and photostability. Structural characterization, photophysical studies, and corresponding theoretical approaches have been made to ensure their fundamental basis. As for dye‐sensitized solar cell applications, it was found that 6–8 possess a larger dye uptake of 2.4 × 10–7 mol cm–2, 1.5 × 10–7 mol cm–2, and 1.3 × 10–7 mol cm–2, respectively, on TiO2 than that of the commercial N3 dye (1.1 × 10–7 mol cm–2). Compound 8 works as a highly efficient photosensitizer for the dye‐sensitized nanocrystalline TiO2 solar cell, producing a 5.65 % solar‐light‐to‐electricity conversion efficiency (compare with 6.01 % for N3 in this study), a short‐circuit current density of 15.6 mA cm–2, an open‐circuit photovoltage of 0.64 V, and a fill factor of 0.57 under standard AM 1.5 irradiation (100 mW cm–2). These, in combination with its superior thermal and light‐soaking stability, lead to the conclusion that the concomitant tridentate binding properties offered by the bipyridine‐pyrazolate ligand render a more stable complexation, such that extended life spans of DSSCs may be expected.
High efficiency green emission is crucial to the designs of energy‐saving display and lighting. Efficient electroluminescent green emitters with both wet‐ and dry‐process feasibility is highly desirable in order to realize, respectively, cost‐effective large roll‐to‐roll manufacturing and high performance products. In this study, high‐efficiency, phosphorescent, green organic light emitting diodes with a novel iridium complex, bis[5‐methyl‐8‐trifluoromethyl‐5H‐benzo(c)(1,5)naphthyridin‐6‐one] iridium (acetylacetonate), are demonstrated. They possess both wet‐ and dry‐processing possibilities. The emitter exhibits a short excited‐state lifetime, 1.25 μs, and a high quantum yield, 69%, due to the efficient intersystem crossing of the ground state to the excited state. Using 4,4′‐bis(carbazol‐9‐yl)biphenyl as a host, the device shows at 1000 cd m−2 an external quantum efficiency (EQE) of 21% and power efficiency of 64 lm W−1 via vapor deposition, while 26% EQE and 69 lm W−1 by spin‐coating, the highest among all reported wet‐processed green organic light emitting diodes. Besides electroluminescence, the high device efficiency may also be attributed to the employed device architecture enabling therein an electron trap to facilitate the injection of this minor carrier against that of a hole, leading to a balanced carrier‐injection, and hence a high carrier recombination and in turn a high device efficiency.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.