Cascade hole transport in efficient green phosphorescent light‐emitting devices achieved by layer‐by‐layer solution deposition using photocrosslinkable‐conjugated polymers containing oxetane side‐chain moieties

Abstract

A hole‐injection/transport bilayer structure on an indium tin oxide (ITO) layer was fabricated using two photocrosslinkable polymers with different molecular energy levels. Two photoreactive polymers were synthesized using 2,7‐(or 3,6‐)‐dibromo‐9‐(6‐((3‐methyloxetan‐3‐yl)methoxy)hexyl)‐9H‐carbazole) and 2,4‐dimethyl‐N,N‐bis(4‐ (4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)phenyl)aniline via a Suzuki coupling reaction. When the oxetane groups were photopolymerized in the presence of a cationic photoinitiator, the photocured film showed good solvent resistance and compatibility with a poly(N‐vinylcarbazole) (PVK)‐based emitting layer. Without the use of a conventional hole injection layer (HIL) of poly(3,4‐ethylenedioxythiophene)/(polystyrenesulfonate) (PEDOT:PSS), the resulting green light‐emitting device bearing PVK: 5‐4‐tert‐butylphenyl‐1,3,4‐oxadiazole (PBD):Ir(Cz‐ppy)3 exhibited a maximum external quantum efficiency of 9.69%; this corresponds to a luminous efficiency of 29.57 cd/A for the device K‐4 configuration ITO/POx‐I/POx‐II/PVK:PBD:Ir(Cz‐ppy)3/triazole/Alq3/LiF/Al. These values are much higher than those of PLEDs using conventional PEDOT:PSS as a single HIL. The significant improvement in device efficiency is the result of suppression of the hole injection/transport properties through double‐layered photocrosslinked‐conjugated polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Modeling of photoactive conjugated donor–acceptor copolymers: the effect of the exact HF exchange in DFT functionals on geometries and gap energies of oligomer and periodic models

“…The initial oligomer model of P1 had a linear and slightly spiral backbone with alternating (10-15) and (0-3) degree dihedral angles between the donor and the acceptor units, while the periodic model had alternating dihedral angles of 4 and À4 degrees creating practically a planar polymer. The initial oligomer model of P2 had a planar zigzag backbone with dihedral angles of (2)(3)(4)(5)(6)(7)(8)(9)(10) degrees between the thiophene and benzotriazole units and of (22)(23)(24)(25) degrees between the thiophene and fluorene units. The periodic model of P2 was constructed of two CRUs to create a relaxed and repeatable structure.…”

“…Relatively low fabrication cost and easy manufacturing make conjugated polymers promising materials for light-emitting diodes, 1,2 field-effect transistors, 3 organic solar cells, 4,5 and chemical sensors. [6][7][8] Conjugated polymers with a donor-acceptor (D-A) architecture have drawn special attention, because alternation of the electron deficient and electron rich moieties in the polymer backbone has been discovered to lower the band gap.…”