Despite myriad challenges, clinicians see room for progress.
Image credit: Shutterstock/David Tadevosian.
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Edited by Tobin J. Marks, Northwestern University, Evanston, IL, and approved October 17, 2003 (received for review July 5, 2003)
Article Figures & SI
Figures
- Fig. 1.
Schematic illustration of OLEDs formed by ScL. (a) A piece of the elastomer poly(dimethylsiloxane) (PDMS) supports thin conducting electrodes of Ti (1 nm)/Au (20–60 nm), and a transparent substrate supports an electroluminescent (EL) layer on indium tin oxide (ITO). (b) When these pieces are brought together, van der Waals forces pull the electrodes into intimate contact with the EL layer at room temperature, without application of external pressure. (c) A reflection image taken with an optical microscope on lamination of Au/PDMS on the EL layer. (Scale bar, 50 μm.)
- Fig. 2.
Characteristics of OLEDs formed from a stack of ITO (100 nm)/MEH-PPV (65 nm)/Au (20 nm), fabricated by ScL and by evaporation (conventional) of the Au layer. (a) Current density as a function of electric field. (b) External quantum efficiency [% photons per electron (ph/el)] as a function of current density. Squares, conventional device operated with ITO positively biased; triangles, ScL device operated with ITO positively biased; circles, conventional device operated with Au positively biased; diamonds, ScL device with Au positively biased. For both bias directions, the efficiency of the ScL device is much higher than that of the conventional device.
- Fig. 3.
Normalized and unnormalized (Insets) PL spectra. (a) PL spectra of 10-nm MEH-PPV films with evaporated Au coatings on half. In the main part of the graphs, the spectra were normalized to the maximum intensities of the PL from the bare regions of the MEH-PPV film (without Au), which were identical for both samples. (b) PL spectra of 10-nm MEH-PPV films with Au coatings formed by ScL on half of it. The films were excited at a wavelength of 420 nm in the uncoated and Au-coated regions by using the same excitation/detection geometry. The data taken from the bare MEH-PPV region are shown in red, and those taken from the Au-coated region are shown in black. The PL from the evaporated Au region is lower in intensity and blue-shifted compared to the regions that do not have Au. In contrast, PL from regions with laminated Au coatings show decreases in intensity but no spectral shift. In the main graphs, the PL intensities are normalized to the peak intensity of the bare film without Au coating.
- Fig. 4.
Patterned OLEDs formed by the combined use of ScL and soft lithography. In all cases, the Au was 20 nm thick and the electroluminescent layer was a polyfluorene derivative blended with 17 wt % of TBABF4 (100 nm). The unpatterned devices showed EL efficiencies of 0.65% ph/el. The schematic illustrations on the left show the modifications to the ScL electrodes, and the images on the right represent an example of OLEDs fabricated by using the approach. (a) Molding features of relief into the PDMS followed by blanket deposition of the electrode generates emission in the pattern of the raised features. (Scale bar, 100 μm.) (b) Microcontact printing an insulating self-assembled monolayer (octadecanethiol; C18) before lamination yields emission only in the bare Au regions. (Scale bar, 100 μm.) (c) Photolithography with a conformable phase mask followed by etching directly patterns lines (150 nm wide) of Au on the PDMS. The averaged linewidth (∼600 nm) of the pattern of emission (graph below) in this case is comparable to the resolution of the optical imaging system. (Scale bar, 5 μm.) The Rayleigh diffraction limit for the 0.55-numerical-aperture microscope objectives is 590 nm at a wavelength of 540 nm. The EL image was taken through the ITO (100 nm)/glass (0.4 mm), which reduces the effective numerical aperture.
Organic light-emitting diodes formed by soft contact lamination
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