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The research on new functional layer materials and optimization of fabrication in organic light-emitting diode (OLED) has been continuously concerned. In this work, phosphotungstic acid solution used as a precursor is spin-coated onto ITO anode, and then a phosphorus-tungsten oxide (WO 3 -P 2 O 5 ) film is obtained after annealing treatment. Various parameters which include film composition, surface morphology, work function and optical property are measured. It suggests that the film has the composition of 24 WO 3 ·P 2 O 5 annealed at 200 °C, which exhibits work function of 5.55 eV, surface root mean square (RMS) roughness value of 1.525 nm and optical transmittance of over 92%. The WO 3 -P 2 O 5 film is used as hole injection layer (HIL), and the OLED with the structure of [ITO/ WO 3 -P 2 O 5 / TPD/ Alq 3 / LiF/ Al] is fabricated. The performance of device shows turn-on voltage of 2.6 V, maximum luminance of 13553 cd/m 2 , maximum current efficiency of 5.87 cd/A and maximum power efficiency of 3.44 lm/W, respectively. The results provide a new way to deposit HIL based on solution-processed metal oxide in efficient OLED. [ABSTRACT FROM AUTHOR]

Highlights: [•] The cold crystallization behavior of TPB and TTB powder and their π–π aggregation in film were studied for the first time. [•] Both TPB and TTB could form smooth film and effective π–π interactions with edge-on orientations. [•] Annealing process is propitious to the formation of more ordered microstructure, resulting in improved carrier mobility. [•] The cold crystallization character of HTMs could be employed to predict their film structural order degree and charge carrier mobility. [ABSTRACT FROM AUTHOR]

In this work, we report a systematic study of the properties of the thermal cross-linkable triarylamine based hole-transporting material (HTM) N,N ′-di- p -tolyl -N,N ′-bis(4-vinylphenyl)-[1,1′-biphenyl]-4,4′-diamine (V-p-TPD) and the distinctive nature of its cross-linked thin films fabricated by solution process under mild thermal polymerization without any initiator. The cross-linked V-p-TPD film exhibited remarkable solution resistance to common solute such as chlorobenzene, toluene, chloroform and tetrahydrofuran. The cross-linked V-p-TPD film showed better morphological stability than vacuum-deposited film of its monomer TPD. The space-charge-limited current (SCLC) measurements revealed that the cross-linked V-p-TPD film afforded comparable hole mobility with vacuum-deposited TPD film. Finally, we applied the cross-linked V-p-TPD film in organic light-emitting diodes (OLEDs) to evaluate its performance in all-solution-processed OLEDs. [ABSTRACT FROM AUTHOR]

Film-forming property of organic semiconductors is one of crucial factors for the performance of flexible organic light-emitting diode. In this work, two hole transporting materials based on triphenylamine were synthesized, which showed an outstanding film-forming property and could form free-standing films with a diameter of 4 mm. The spin-coated films on the flexible substrates showed an unobvious mechanical failure bended with radius of curvature no less than 6 mm. Photoelectron yield spectroscopy show that the two compounds embody suitable highest occupied molecular orbital levels (−5.14 eV and −5.25 eV) for hole injection. The sandwiched organic light-emitting diodes use poly[2-(4-3′,7′-dimethyloctyloxy)-phenyl]- p -phenylenevinylene) as emitting and electron transporting layer showed higher stability with increasing operation current density, an maximum luminance level of 103,690 cd m −2 . It demonstrate that the as-synthesized hole transporting materials hold a promising in high brightness flexible organic light-emitting diodes. [ABSTRACT FROM AUTHOR]