Solution-processed thermally stable amorphous films of small molecular hole injection/transport bi-functional materials and their application in high efficiency OLEDs?

Journal of Materials Chemistry C Pub Date: 2015-10-02 DOI: 10.1039/C5TC02559A

Abstract

A series of novel triphenylamine-based small molecular hole transport materials (HTMs) are reported for solution processed organic light-emitting devices (OLEDs). The character of this series of HTMs, denoted as TPD(BTPA)n (n = 1, 2, 4), is connecting the flexible moieties of butadiene bridged triphenylamine (BTPA) to N,N,N′,N′-tetraphenyl-[1,1′-biphenyl]-4,4′-diamine (TPD). The glass transition temperature and crystallization temperature (Tg and Tc) showed a proportional relationship with the number of BTPA moieties. The Tg value of TPD(BTPA)4 can be up to 125.5 °C, which is higher than most of the reported small molecular HTMs (Tg: 54–116 °C). The TPD(BTPA)4 spincoated film showed an outstanding thermal stability which remained amorphous even when annealed at 110 °C, for 48 h. This indicated that the breaking of the planar molecular structure with BTPA moieties can suppress intermolecular stacking. The solution processed OLEDs with 8-hydroxyquinoline aluminum (Alq3) as emission and electron transport layers showed high stability at high operation current (>400 mA cm?2). The OLED with TPD(BTPA)4 achieved a maximum current efficiency of 5.83 cd A?1 (at the operation current density > 400 mA cm?2), which is higher than the maximum current efficiency of most evaporation and solution processed OLEDs in identical structures.

Graphical abstract: Solution-processed thermally stable amorphous films of small molecular hole injection/transport bi-functional materials and their application in high efficiency OLEDs
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