Hole-transporting polyimide for organic electroluminescent display

• Published in: Thin solid films Vol. 363; no. 1; pp. 263 - 267
• Main Authors: Kim, Youngkyoo, Lee, Jae-Gyoung, Han, Kijong, Hwang, Ha-Keun, Choi, Dong-Kwon, Jung, Young-Yi, Keum, Ji-Hwan, Kim, Sunwook, Park, Seong-Sik, Im, Woo-Bin
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2000
• Subjects: Capacitance–temperature; Hole-transporting polyimide; Organic electroluminescent device; Rectifying behavior; Relaxation temperature; Vapor deposition polymerization; Rectifying behavior; Relaxation temperature; Vapor deposition polymerization; Organic electroluminescent device; Capacitance–temperature; Hole-transporting polyimide
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/S0040-6090(99)01073-1

The thermal stability of newly synthesized hole-transporting polyimide, poly[ N,N′–diphenyl– N,N′–bis(4–aminobiphenyl)–(1,1′–biphenyl)–4,4′–diamine pyromellitimide] (PMDA-DBABBD PI), via vapor deposition polymerization was investigated with the aid of the capacitance–temperature ( C– T) measurement technique. Prior to the examination of the complete organic electroluminescent device (OELD), the single layer devices with the individual materials including tris(8-hydroxyquinolinato) aluminum (Alq 3), N,N′-diphenyl- N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD), N,N′-diphenyl- N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB), copper phthalocyanine (CuPc), and PMDA-DBABBD PI were subjected to the C– T measurement. The relaxation temperatures of the single layer devices with Alq 3, TPD, NPB, CuPc, and PMDA-DBABBD PI were 180, 76, 110, 125, and more than 200°C, respectively. The OELD with PMDA-DBABBD PI and Alq 3 as a hole-transporting layer and emissive layer was not relaxed up to 150°C, while those containing CuPc/TPD and NPB thin films were catastrophically damaged at ca. 76 and 110°C, respectively. The OELD with the small organic hole-transporting molecule has almost the same relaxation temperature as the single layer device with the respective molecules. The rectifying and electroluminescent characteristics disappeared for the annealed OELD with the small organic hole-transporting molecules, whereas the OELD with the hole-transporting polyimide did still show the rectifying behavior with the green light emission even though the current density and the light intensity became largely reduced.