Methods and apparatus of spatially resolved electroluminescence of operating organic light-emitting diodes using conductive atomic force microscopy
A conductive atomic force microscopy (cAFM) technique which can concurrently monitor topography, charge transport, and electroluminescence with nanometer spatial resolution. This cAFM approach is particularly well suited for probing the electroluminescent response characteristics of operating organic light-emitting diodes (OLEDs) over short length scales.
1. A method of using conductive atomic force microscopy for spatially-resolved electroluminescence of an organic light-emitting diode, said method comprising:
providing an operative organic light-emitting diode device comprising an anode, a cathode and at least one emissive organic component therebetween;
contacting one of said device electrodes with a conductive atomic force microscope, said microscope comprising a current conductive cantilever tip;
applying a bias across said device; and
correlating electroluminescence with tip position on said device.
2. The method of claim 1 wherein said tip is at a position on one of said electrodes and said bias is varied.
3. The method of claim 2 wherein light emission intensity and current density are detected as a function of applied bias.
4. The method of claim 1 wherein said bias is applied over the surface of one of said device electrodes.
5. The method of claim 1 wherein said device is topographically mapped.
6. The method of claim 4 wherein light emission intensity and current density are mapped simultaneously with said device topography.
7. The method of claim 1 wherein said device comprises a pixel and said bias is applied across said pixel.
8. The method of claim 7 wherein light emission intensity and current density are detected as a function of distance.
9. The method of claim 1 wherein said bias is applied over the surface of said device.
10. The method of claim 9 wherein spatial variations of quantum efficiency are correlated with light emission.
11. A conductive atomic force microscope apparatus to spatially-resolve electroluminescence of a diode device, said apparatus comprising:
a probe comprising a current conductive cantilever tip;
an optics component opposite said cantilever tip, said component comprising a bi-convex lens arranged and configured to direct light emitted from a diode device; and
a photomultiplier component aligned with said cantilever tip and said optics component for light detection.
12. The apparatus of claim 11 wherein said photomultiplier component is peripheral to an apparatus scanner.
13. The apparatus of claim 11 wherein said photomultiplier component is vertically aligned with an apparatus scanner.
14. The apparatus of claim 11 wherein said photomultiplier component is coupled to an inverted optical microscope.
15. The apparatus of claim 14 comprising a spectrophotometer to determine emitted light wavelength.
16. A method of operating a conductive atomic force microscope to spatially-resolve electroluminescence, said method comprising:
providing an operative organic light-emitting diode device comprising an anode, a cathode and at least one emissive organic component therebetween;
contacting one of said device electrodes with a conductive atomic force microscope apparatus, said apparatus comprising a current conductive cantilever tip and a scanner component;
focusing light emitted from said device; and
amplifying said light with a photomultiplier component.
17. The method of claim 16 comprising measurement of current flow through said tip and calculation of device quantum efficiency.
18. The method of claim 16 wherein said photomultiplier component is positioned between said device and said scanner component.
19. The method of claim 16 wherein said emitted light is focused through an inverted optical microscope.
20. The method of claim 19 comprising analysis of optical and electrical spectra of said emitted light.