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We demonstrate an electrically-driven metal-dielectric photonic crystal emitter by fabricating a series of organic light emitting diode microcavities in a vertical stack. The states of the individual microcavities are shown to split into bands of hybridized photonic energy states through interaction with adjacent cavities. The propagating photonic modes within the crystal depend sensitively on the unit cell geometry and the optical properties of the component materials. By systematically varying the metallic layer thicknesses, we show control over the density of states and band center. The emergence of a tunable photonic band gap due to an asymmetry-introduced Peierls distortion is demonstrated and correlated to the unit cell configuration. This work develops a class of one dimensional, planar, photonic crystal emitter architectures enabling either narrow linewidth, multi-mode, or broadband emission with a high degree of tunability.

Encasing an OLED between two planar metallic electrodes creates a Fabry–Pérot microcavity, resulting in significant narrowing of the emission bandwidth. The emission from such microcavity OLEDs depends on the overlap of the resonant cavity modes and the comparatively broadband electroluminescence spectrum of the organic molecular emitter. Varying the thickness of the microcavity changes the mode structure, resulting in a controlled change in the peak emission wavelength. Employing a silicon wafer substrate with high thermal conductivity to dissipate excess heat in thicker cavities allows cavity thicknesses from 100 to 350 nm to be driven at high current densities. Three resonant modes, the fundamental and first two higher harmonics, are characterized, resulting in tunable emission peaks throughout the visible range with increasingly narrow bandwidth in the higher modes. Angle resolved electroluminescence spectroscopy reveals the outcoupling of the TE and TM waveguide modes which blue-shift with respect to the normal emission at higher angles. Simultaneous stimulation of two resonant modes can produce dual peaks in the violet and red, resulting in purple emission. These microcavity-based OLEDs employ a single green molecular emitter and can be tuned to span the entire color gamut, including both the monochromatic visible range and the purple line.

Vertically‐stacked organic light emitting diode (OLED) microcavities form 1D metal‐dielectric photonic crystals (MDPC) with many degrees of freedom for engineering complex emission profiles. The photonic band structure of the MDPC OLED is determined by the underlying unit cell and is particularly sensitive to the properties of the metallic electrodes. The electronic requirements of microcavity OLED fabrication often necessitate dissimilar metallic electrodes to achieve good performance. This can profoundly impact the photonic properties of a MDPC by doubling the unit cell length. This work presents a MDPC OLED formed with single‐cavity unit cells by employing optically similar Ag alloys as the semi‐transparent electrode materials. The crystal is found to display a single photonic band without a band gap up to eight stacked cavities. The states within the band are evenly‐spaced and clearly resolved, which is critical for applications seeking to utilize specific photonic states. Design considerations are presented for optimizing the photonic behavior of MDPC OLEDs through selective control of the optical properties of metallic alloys.

Millimeter‐long organic fiber arrays of intramolecular charge transfer merocyanine HB194 dye were prepared by evaporation‐induced self‐assembled method. X‐ray diffraction spectroscopy indicated individual fibers are millimeter‐sized HB194 single crystals. The elimination of defects and structural disorder enabled photoluminescence microscopy studies that revealed the intramolecular charge transfer (CT), bandgap excitonic state is long‐lived and remains largely localized in the absence of π‐orbital stacking in the crystalline structure. These nanosecond lifetimes explain the observation of a photoconductivity response upon irradiation with a 633 nm laser due to dissociation of the delocalized CT exciton to free carriers. At the same time, the photo response was increased 4.5 times by coating of the HB194 fiber array with polyvinyl alcohol. This increase is attributed to the larger dielectric field around the fibers that further facilitates the band‐gap (CT) exciton dissociation.