Abstract
Super-resolution stimulated emission depletion (STED) microscopy is adapted here for materials characterization that would not otherwise be possible. With the example of organic light-emitting diodes (OLEDs), spectral imaging with pixel-by-pixel wavelength discrimination allows us to resolve local-chain environment encoded in the spectral response of the semiconducting polymer, and correlate chain packing with local electroluminescence by using externally applied current as the excitation source. We observe nanoscopic defects that would be unresolvable by traditional microscopy. They are revealed in electroluminescence maps in operating OLEDs with 50 nm spatial resolution. We find that brightest emission comes from regions with more densely packed chains. Conventional microscopy of an operating OLED would lack the resolution needed to discriminate these features, while traditional methods to resolve nanoscale features generally cannot be performed when the device is operating. This points the way towards real-time analysis of materials design principles in devices as they actually operate.
Highlights
Super-resolution stimulated emission depletion (STED) microscopy is adapted here for materials characterization that would not otherwise be possible
The underlying polymer physics, known in principle, shows that the useful functions depend on the complex chain morphology in spin-cast films[15,16,17,18,19], the relevant length scales of chain organization lying below the diffraction limit and below the capability to characterize by conventional optical methods
To achieve super-resolution, we focus a doughnut-shaped continuous wave (CW) depletion beam, shifted to the red of the electroluminescence, onto the field-of-view region to selectively quench the majority of emissive states (Fig. 2b), we scan the sample across the pinhole to collect an image
Summary
Super-resolution stimulated emission depletion (STED) microscopy is adapted here for materials characterization that would not otherwise be possible. Conventional microscopy of an operating OLED would lack the resolution needed to discriminate these features, while traditional methods to resolve nanoscale features generally cannot be performed when the device is operating This points the way towards real-time analysis of materials design principles in devices as they operate. Two specific adaptations of the usual STED microscopy are critical to accomplish this study: (1) electroluminescence-STED (EL-STED) to image electroluminescence maps with roughly 50-nm resolution in the x–y plane, and (2) STED-spectral imaging to map local-chain morphology in the emissive layer through differences in spectral response Using these new techniques concurrently allows one to directly correlate nanoscopic defects with local-chain packing
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