Peformance enhancement of organic light-emitting diodes based on different hole transport layers

Three Organic light-emitting diodes (OLEDs) were fabricated by conventional vacuum deposition method using N, N-'-biphenyl-N, N-'-bis(3-methylphenyl)-1, 1-biphenyl-4, 4'-diamine (TPD) and 2, 7-bis(p-methoxyphenyl-m-tolyl- amino)-9, 9dimethylfluorene (TPF-OMe, a derivative of TPD) as a hole transport layer, respectively, and tris (8-hydroxyquinolinato) aluminum (Alq) as an electron transport and emissive layer. The structures of the devices are ITO/TPD(30 nm)/Alq(50 nm)/Mg:Ag(300 nm) (A), ITO/TPF-OMe(30 nm)/Alq(50 nm)/Mg:Ag(300 nm) (B), and ITO/TPF-OMe(20 nm)/TPD(10 nm)/Alq(50 nm)/Mg:Ag(300nm) (C). The results showed that device A showed the maximum luminance of 10605cd/m(2) at 15V, and maximum luminance efficiency was 0.86 lm/W at 5.5V. Device B and C showed the luminance of 3894ed/m(2) and 14720 cd/m(2) at 15V with the maximum luminance efficiency of 0.56 lm/W at 4V and 1.06 lm/W at 4.5V, respectively. The thermal stability of OLEDs was investigated at 10v.