Integration of organic light emitting diodes (OLEDs) and organic photodetectors (OPDs) on flexible plastic substrates promises compact and low-cost optical detection units for multiplex sensors. These units may be laminated to a microfluidic system for sensing applications in a liquid. Here, a 6 × 6 element matrix of alternating blue OLEDs and OPDs is demonstrated on a single flexible plastic substrate. The devices are fabricated by masked thermal evaporation on a 200 µm thick polyethylene terephthalate (PET) foil. The individual device size is 1 mm × 1 mm. Both OLEDs and OPDs are demonstrated to work. The spectral characteristics are shown to be suitable for fluorescence measurements. Signals from fluorescence-labeled spots above the OPDs under OLED excitation are investigated. Successful operation of the OLED-OPD matrix for reflection measurement is demonstrated.

The application of nanopatterned electrode materials is a promising method to improve the performance of thin-film optoelectronic devices such as organic light-emitting diodes (OLEDs) and organic photovoltaics. Light coupling to active layers is enhanced by employing nanopatterns specifically tailored to the device structure. A range of different nanopatterns is typically evaluated during the development process. Fabrication of each of these nanopatterns using electron-beam lithography is time- and cost-intensive, particularly for larger-scale devices, due to the serial nature of electron beam writing. Here, we present a method to generate nanopatterns of varying depth with different nanostructure designs from a single one-dimensional grating template structure with fixed grating depth. We employ multiple subsequent steps of UV nanoimprint lithography, curing, and ion beam etching to fabricate greyscale two-dimensional nanopatterns. In this work, we present variable greyscale nanopatterning of the widely used electrode material indium tin oxide. We demonstrate the fabrication of periodic pillar-like nanostructures with different period lengths and heights in the two grating directions. The patterned films can be used either for immediate device fabrication or pattern reproduction by conventional nanoimprint lithography. Pattern reproduction is particularly interesting for the large-scale, cost-efficient fabrication of flexible optoelectronic devices.

Charge injection at metal-organic interfaces often limits the electric current in organic light-emitting diodes without additional injection layers. Integrated nanopatterned electrodes may provide a way to overcome this current injection limit by local field enhancements leading to locally space charge–limited currents. We compare electrical characteristics of planar and nanopatterned hole-only devices based on the charge transport material NPB with different thicknesses in order to investigate the nanopattern’s effect on the current limitation mechanism. Integration of a periodic nanograting into the metal electrode yields a current increase of about 1.5 to 4 times, depending on thickness and operating voltage. To verify the experimental results, we implement a finite element simulation model that solves the coupled Poisson and driftdiffusion equations in a weak form. It includes space charges, drift and diffusion currents, non-linear mobility, and charge injection at the boundaries. We find in experiment and simulation that the planar devices exhibit injection-limited currents, whereas the currents in the nanopatterned devices are dominated by space charge effects, overcoming the planar injection limit. The simulations show space charge accumulations at the corners of the nanopattern, confirming the idea of locally space charge–limited currents.