Abstract
Three phosphine sulfide-based bipolar host materials, viz CzPhPS, DCzPhPS, and TCzPhPS, were facilely prepared through a one-pot synthesis in excellent yields. The developed hosts exhibit superior thermal stabilities with the decomposition temperatures (Td) all exceeding 350 °C and the melting temperatures (Tm) over 200 °C. In addition, their triplet energy (ET) levels are estimated to be higher than 3.0 eV, illustrating that they are applicable to serve as hosts for blue phosphorescent organic light-emitting diodes (PhOLEDs). The maxima luminance, current efficiency (CE), power efficiency (PE), and external quantum efficiency (EQE) of 17,223 cd m−2, 36.7 cd A−1, 37.5 lm W−1, and 17.5% are achieved for the blue PhOLEDs hosted by CzPhPS. The PhOLEDs based on DCzPhPS and TCzPhPS show inferior device performance than that of CzPhPS, which might be ascribed to the deteriorated charge transporting balance as the increased number of the constructed carbazole units in DCzPhPS and TCzPhPS molecules would enhance the hole-transporting ability of the devices to a large extent. Our study demonstrates that the bipolar hosts derived from phosphine sulfide have enormous potential applications in blue PhOLEDs, and the quantity of donors should be well controlled to exploit highly efficient phosphine sulfide-based hosts.
Highlights
Phosphorescent organic light-emitting diodes (PhOLEDs) have been extensively researched in recent decades since they can achieve an internal quantum efficiency of nearly100% by harvesting both singlet and triplet excitons, and have the advantages of excellent device stability, high color purity, as well as flexible color adjustment [1,2,3]
The blue PhOLED hosted by CzPhPS achieves a low turn-on voltage of 3.1 eV and a maximum external quantum efficiency (EQE) of 17.5%, better than the device performance of DCzPhPS and Tris(4-(9H-carbazol-9-yl)phenyl)phosphine Sulfide (TCzPhPS), which could be owed to its better charge transport balance
CzPhPS, DCzPhPS, display ascribed to the π-π* transitions of carbazole groups [27], whereas the absorption peaks of around 335 and 343 nm might be due to the intramolecular charge transfer (CT) from the electron donor carbazole to the electron acceptor triphenyl phosphine sulfide
Summary
Phosphorescent organic light-emitting diodes (PhOLEDs) have been extensively researched in recent decades since they can achieve an internal quantum efficiency of nearly. We prepared the APS-based host DPSSi ((9-(4-(triphenylsilyl)phenyl)-9H-carbazole-3,6-diyl) bis(diphenyl-phosphine sulfide), Scheme 1), whose blue PhOLED shows a maximum. EQE of 20.8%, which is 1.58 folds of enhancement compared to that of the APO-based host DPOSi ((9-(4-(triphenylsilyl)phenyl)-9H-carbazole-3,6-diyl)bis(diphenylphosphine oxide), Scheme 1) in the same device structure [26]. All three compounds possess the high ET s of ~3.0 eV, much higher than those of the commonly used blue emitters, demonstrating that they are promising candidates as the hosts for blue OLEDs. The blue PhOLED hosted by CzPhPS achieves a low turn-on voltage of 3.1 eV and a maximum EQE of 17.5%, better than the device performance of DCzPhPS and TCzPhPS, which could be owed to its better charge transport balance.
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