Organic electronics has recently gained attention as a new field promising cheaper, flexible, and large-scale
devices. Although photolithography has proven to be a high-resolution and high-throughput patterning method with
excellent registration capabilities, the emerging field of organic electronics has been largely unsuccessful in adapting this
well-established method as a viable approach to patterning. Chemical compatibility issues between organic materials and
the processing solvents and chemicals required by photolithography have been the main problem. This challenge has led
us to identify a set of non-damaging processing solvents and to develop alternative imaging materials in order to extend
photolithographic patterning methods to organic electronics.
We have identified supercritical carbon dioxide and hydrofluoroether (HFE) solvents as chemically benign to
organic electronic materials and which are also suitable as processing solvents. We refer to these solvents as orthogonal
in that they do not substantially interact with traditional aqueous and organic solvents. Multi-layered devices are easily
realized by exploiting this orthogonality property; subsequent layers are deposited and patterned without damaging or
otherwise adversely affecting previously deposited underlying layers. We have designed and synthesized novel
photoresists, which are processible in these benign solvents.
A family of conjugated polymers with fused structures consisting of three to five
thiophene rings and with the same alkyl side chains has been synthesized as a means to
understand structure - property relationships. All three polymers showed well extended
conjugation through the polymer backbone. X-ray diffraction study of the polymer thin
films suggests that the polymer with the even number of fused thiophene rings forms a
tight crystalline structure due to its tilted side chain arrangement. On the other hand, the
polymers with the odd number of fused thiophene rings packed more loosely.
Characterization in a field-effect transistor configuration showed that the mobility of the
polymer with the even number of rings is one order of magnitude higher than its oddnumbered
counterparts. Through this structure - property study, we demonstrate that
proper design of the molecules and properly arranged side chain positions on the polymer
backbone can greatly enhance polymer electronic properties
In this paper, the effects of hole injection layer (HIL) on the performance of typically used tris-(8-hydroxyquinoline) aluminum (Alq<sub>3</sub>) based OLEDs have been investigated. Three different HIL materials were used: copper phthalocyanine (CuPc), magnesium phthalocyanine (MgPc) and zinc phthalocyanine (ZnPc). The Metallophthalocyanines (MPcs) will be used to construct single hole injection layer (HIL) and double HIL (<i>d</i>-HIL). In the OLEDs, Alq<sub>3</sub> acts as the emitting layer and electron transport layer. Although <i>d</i>-HIL structures show higher efficiency than that of the reference device, the highest current efficiency ~ 4.02 cd/A corresponds to the 15 nm ZnPc HIL device. Compared to an current efficiency of ~3.29 cd/A and a power efficiency of ~0.99 lm/W (at 100 cd/m<sup>2</sup> luminance) of the reference device, an 15 nm ZnPc HIL device has ~22% higher current efficiency and ~67% higher power efficiency. The reasons for the improvements will be discussed.
By engineering a new cohosting system of tris(8-hydroxyquinoline) and 4,7-diphenyl-1,10-phenanthroline in the electron transport layer, the current efficiency of the organic light emitting diode is improved by more than 20% while the bias is reduced by ~40% as compared to the device with a single host of Alq<sub>3</sub> as the electron transport layer. The maximum luminance is over 16000 cd/m<sup>2</sup> at the bias of 22V and the current of 475mA/cm<sup>2</sup>, which is ~73% higher than the single host Alq<sub>3</sub> device without optimizing the layer thickness. The lifetime under ambient environment is enhanced by a factor of ~1.8. The reasons for the improvement will be investigated. The results strongly indicate that the knowledge of bulk conductivity engineering of organic n-type transporters shows practical significance in OLED applications.