TY  - JOUR
A1  - Bagnich, Sergey A.
A1  - Unger, Th.
A1  - Jaiser, F.
A1  - Neher, Dieter
A1  - Thesen, M. W.
A1  - Krüger, H.
T1  - Efficient green electrophosphorescence based on ambipolar nonconjugated polymers evaluation of transport and emission properties
JF  - Journal of applied physics
N2  - New materials for polymer organic light-emitting diodes based on a polymer matrix doped with phosphorescent dyes are presented. The matrix system is based on a polystyrene backbone bearing either electron or hole transporting units at the 4-position of each repeat unit. Random copolymers and polymer blend systems of the homopolymers are prepared, both with 62 wt.% electron transporting and 38 wt.% hole transporting moieties. Adding a green electrophosphorescent dye to the polymer matrix leads to efficient electroluminescence with a maximum current efficiency of 35 cd/A and a maximum external quantum efficiency of up to 10%. The mobilities of electrons and holes in the dye-doped copolymer, as measured by transient electroluminescence, are around 5 x 10(-5) and 5 x 10(-6) cm(2)/Vs, respectively, while the blend of the two homopolymers exhibits slightly lower mobilities of both types of carriers. Despite the pronounced imbalance of charge transport, the device performance is almost entirely limited by the phosphorescence efficiency of the dye, implying balanced flow of holes and electrons into the active region. Also, devices made with either the copolymer or the blend yielded very similar device efficiencies, despite the noticeable difference in electron and hole mobility. It is proposed that electrons are efficiently blocked at the interlayer and that the so-formed space charge assists the balanced injection of holes.
Y1  - 2011
U6  - https://doi.org/10.1063/1.3618681
SN  - 0021-8979
SN  - 1089-7550
VL  - 110
IS  - 3
PB  - American Institute of Physics
CY  - Melville
ER  -