Optically‐Pumped Lasing in Hybrid Organic–Inorganic Light‐Emitting Diodes

Abstract

Here, the use of metal oxide layers both for charge transport and injection into an emissive semiconducting polymer and also for the control of the in‐plane waveguided optical modes in light‐emitting diodes (LEDs) is reported. The high refractive index of zinc oxide is used to confine these modes away from the absorbing electrodes, and include a nano‐imprinted grating in the polymer layer to introduce distributed feedback and enhance optical out‐coupling. These structures show a large increase in the luminescence efficiency over conventional devices, with photoluminescence efficiency increased by up to 45%. Furthermore, optically‐pumped lasing in hybrid oxide polymer LEDs is demonstrated. A tuneable lasing emission is also obtained in a single device structure by employing a graduated thickness of a zinc oxide inter‐layer. This demonstrates the scope for using such architectures to improve the external efficiency of organic semiconductor LEDs, and opens new possibilities for the realization of polymer injection lasers.

Organic solid‐state integrated amplifiers and lasers

“…The third bottleneck is the absence of satisfactory design concepts for laser resonators that can accommodate charge-injecting electrode contacts without introducing high optical losses in the gain material through their interaction with the optical mode. To address this technical difficulty and enhance the prospects for realization of electrical pumping considerable research efforts have been expended so far on the development of resonator architectures that can ensure either optically-pumped laser operation with electrodes [81,[350][351][352], or minimization of the impact of the contact electrodes on waveguide losses [185,353,354]. The solutions proposed involved resonators based either on OLEDs [185,350,351,355,356] or on ambipolar lightemitting field-effect transistors (LEFETs) [81,352,354].…”

Highly efficient inverted polymer light-emitting diodes using surface modifications of ZnO layer

“…However, the charge injection and transport are unbalanced in iPLEDs that use ITO or fluorine-doped tin oxide (FTO) as the cathode; n-type metal oxide, such as zinc oxide (ZnO), hafnium oxide (HfO 2 ) or zirconium oxide (ZrO 2 ), as the electron-injection/transport layer; poly(9,9 0 -dioctylfluorene-cobenzo-thiadiazole) (F8BT) or poly(phenylvinylene): super yellow as the emissive layer; molybdenum oxide (MoO 3 ) or nickel oxide (NiO) as hole injection/transport layer and gold (Au) as the anode. In fact, the hole injection in this type of device indicates an ohmic contact from the MoO 3 /Au to the highest occupied molecular orbital level of the emissive layer 25,26 , whereas the electroninjection rates are fairly low because of the considerable energy barrier difference between the conduction band (CB) of the n-type metal oxides and the lowest unoccupied molecular orbital (LUMO) of the emissive layer [9][10][11][12][13][14][15][16][17][27][28][29][30] . Recently, various strategies have been applied to promote electron injection and transport by controlling the interface between the CB of the n-type metal oxide and the LUMO of the emissive layer by using an interlayer, such as ionic liquid molecules (ILMs) 27 , conjugated polyelectrolyte 28,29 , self-assembled dipole monolayer 15 Here we show highly efficient iPLEDs by introducing a spontaneously formed ripple-shaped nanostructure of ZnO (ZnO-R) and applying an amine-based polar solvent treatment using 2-methoxyethanol (2-ME) and ethanolamine (EA) cosolvents (2-ME þ EA) to the ZnO-R.…”

“…However, there are certain critical obstacles impeding the realization of highly efficient iPLEDs. In particular, the majority of the light generated in the polymeric emissive layer is fully reflected and trapped by in-plane waveguide (WG) optical modes because of the use of high-reflective-index layers such as metaloxide (n MO B1.8-2.4) as the electron-injection layer, which results in low Z e values for iPLEDs [14][15][16][17] .…”

Electrically Tunable Organic Distributed Feedback Lasers Embedding Nonlinear Optical Molecules

“…In these systems, the integration of electrically tunable lasers would greatly enhance both detection sensitivity, by modulation of the laser intensity or frequency, and capability of parallel optical processing by multi-wavelength excitation. [ 13 ] The emission of organic distributed feedback (DFB) lasers has been previously tuned by mechanical stretching, [ 14 ] by exploiting a "wedge shape" active [ 15 ] or intermediate high index layer, [ 16 ] or by photoisomerizable azo-polymers. [ 17 ] The basic idea of all these approaches is the variation of the DFB period ( Λ ) or of other geometric characteristics and, consequently, of the effective refractive index (n eff ), since the emission wavelength ( λ ) is given by the Bragg condition, m λ = 2 n eff Λ , where m is the diffraction order.…”