Organic light-emitting devices with in situ postgrowth annealed organic layers

摘要

A comparative study of in situ postgrowth annealing of organic layers before metal cathode was conducted on tris-(8-hydroxyqunoline) aluminum (Alq_3)-based organic light-emitting devices (OLEDs). The devices were fabricated in the same ran with a standard device without annealing for comparison, with an identical structure of indium tin oxide (ITO)/copper phthalocyanine (CuPc) (10 nm)/N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB) (90 nm)/Alq_3 (90 nm)/ Mg:Ag (200 nm)/Ag (20 nm). The annealing temperature used was 60, 80, and 100℃, respectively. It was found that, in situ postgrowth annealing improves the device performance, and annealing near the glass transition temperature of NPB (99.7℃), improves device performance drastically. Power efficiency and current efficiency increase significantly with the annealing temperature, except the current efficiency for device annealed at 100℃ is slightly lower than that of the standard device. The voltage and current density for 100 cd/m~2 luminance are 5.6 V and 4.4 mA/cm~2, respectively, for the device annealed at 100℃, in comparison to 9.2 V and 4.3 mA/cm~2, respectively, for the standard device, the power efficiency is much improved by more than 40%. The in situ postgrowth annealed organic layers were characterized by photoluminescence and Raman spectroscopy.