Efficient light extraction from organic light emitting diode (OLED) is challenging and efforts are being made to come up with efficient & cost effective outcoupling techniques. We demonstrate 50% EQE entitlement from solution processed white OLEDs compared to 33% EQE observed in devices, implying that there is plenty of room to improve the efficiency of white OLEDs. We present challenges in efficient light extraction from solution processed OLEDs that need to be overcome to close the efficiency gap. We also demonstrate a novel characterization technique that is effective in estimating the light extraction efficiency of outcoupling films and can expedite the selection and optimization of various light extraction approaches without the need to build OLEDs.
Here we present recent progress in developing efficient wet-coated organic light-emitting
devices (OLEDs) for lighting applications. In particular, we describe a novel approach
for building efficient wet-coated dye-doped blue phosphorescent devices. Further, a novel
approach for achieving arbitrary emission patterning for OLEDs is discussed. This approach
utilizes a photo-induced chemical doping strategy for selectively activating charge injection
materials, thus enabling devices with arbitrary emission patterning. This approach may provide
a simple, low cost path towards specialty lighting and signage applications for OLED
A series of phenol-capped, oligofluorenes having 2,3,5 and 7 fluorene units and a statistical oligomer with an average of about 10 fluorene units was prepared. In a similar fashion, phenol-capped oligomers having various charge-transporting moieties incorporated into the oligomeric structures were prepared. Polymers were prepared from the oligomers by various linking reactions involving the phenol groups. Trends in the optical and electrical properties as a function of oligomer length will be reported. Device data for this family of emissive copolymers indicates that charge mobility increases with conjugation length, and can be as good as or better than that of an analogous fluorene homopolymer.
Organic light-emitting devices (OLEDs) have shown great promise for general lighting applications. Over the past several years, tremendous progress has been made in improving performance attributes such as light quality, efficacy and lifetime of OLEDs. However, achieving the low cost manufacturing potential of OLEDs, another stringent requirement to enable lighting applications, has so far not been well addressed and explored. Here, we describe a vacuum-free, direct lamination process that could reduce OLED manufacturing costs substantially below what is currently possible. With this technique, OLEDs can be made by laminating an anode component to a separately engineered cathode component using a roll laminator. When coupled with a solution-based chemical n-doping strategy to enable efficient electron injection from an inert cathode into polymeric organic semiconductors, the lamination technique is able to produce high performance OLEDs with efficiency comparable to conventionally fabricated devices utilizing a vacuum-deposited, reactive metal cathode.
Bilayers of aluminum (Al) and alkali fluoride (such as sodium fluoride) are well-known top cathode contacts for organic light-emitting devices (OLEDs) in which the alkali fluoride is inserted in between the Al and organic materials. However, the configuration, to date, has never been successfully applied as bottom cathode contacts. In this article, we describe a novel bilayer bottom cathode contact for OLEDs utilizing the same materials but with a reversed structure, i.e. the Al rather than the alkali fluoride contacts the organic material. Electron-only devices were fabricated showing enhanced electron injection from this bottom contact with respect to an Al-only contact. Kelvin probe, X-ray photoelectron spectroscopy, Auger electron spectroscopy experiments and thermodynamic calculations suggest that the enhancement results from n-doping of the organic material by dissociated alkali metals.
Photovoltaic cells require deposition of a platinum layer at the cathode to serve as a catalyst for reduction of redox carriers in PV cells. Current dye-sensitized solar cells (DSSC) employ high temperature decomposition of chloroplatinic acid to give platinum islands. In order to produce DSSCs with plastic substrates, a low temperature platinum deposition process was developed. Initial experiments showed that platinum was deposited if Karstedt platinum catalyst solution in hexamethyldisilazane (HMDZ) was coated onto a substrate followed by heating under 150°C. PV cell performance of Karstedt-HMDZ-containing platinum was inferior to cells made with high temperature platinum. However, CODPtMe<sub>2</sub> (COD = 1,5-cyclooctadiene) was found to be a platinum precursor that led to PV cell performance equivalent to that obtained from high temperature platinum. Other precursors were evaluated as well including MeCpPtMe<sub>3</sub> that permitted platinum deposition via UV irradiation. Kelvin Probe analysis was also performed on several platinum films prepared from a variety of precursors on several substrates under a variety of conditions. CPD values of
< -0.6eV appeared to predict good PV cell performance. Further application of the low temperature-derived platinum films was made for organic light emitting diodes.