Ultrastrong coupling in Super Yellow polymer microcavities and development of highly efficient polariton light-emitting diodes and light-emitting transistors

Abstract

We present detailed studies on exciton-photon coupling and polariton emission based on a poly(1,4-phenylenevinylene) copolymer, Super Yellow (SY), in a series of optical microcavities and optoelectronic devices, including light-emitting diode (LED) and light-emitting transistor (LET). We show that sufficiently thick SY microcavities can generate ultrastrong coupling with Rabi splitting energies exceeding 1 eV and exhibit spectrally narrow, nearly angle-independent photoluminescence following lower polariton (LP) mode dispersion. When the microcavity is designed with matched LP low-energy state and exciton emission peak for radiative pumping, the conversion efficiency from exciton to polariton emission can reach up to 80%. By introducing appropriate injection layers in a SY microcavity and optimizing the cavity design, we further demonstrate a high-performance ultrastrongly coupled SY LED with weakly dispersive electroluminescence along LP mode and a maximum external quantum efficiency (EQE) of 2.8%. Finally, we realize an ultrastrongly coupled LET based on vertical integration of a high-mobility ZnO transistor and a SY LED in a microcavity, which enables a large switching ratio, uniform emission in the ZnO pattern, and LP mode emission with a maximum EQE of 2.4%. This vertical LET addresses the difficulties of achieving high emission performance and precisely defining the emission area in typical planar LETs, and opens up the possibility of applying various strongly coupled emitters for advanced polariton devices and high-resolution applications.

High-Brightness Blue Polariton Organic Light-Emitting Diodes

“…The jVL characteristics of the cavity BE-POLED indicate a similar behavior, with a luminance of 6871 cd/m 2 at 5 V but a lower EQE of 1.0%, which results from the spectral shift of the peak of its emission spectrum to 473 nm. Nevertheless, both devices show a luminance of above 10,000 cd/m 2 at higher voltages, which is high when compared to most previous demonstrations of POLEDs, 38,16,39 in particular for a blue-emitting device. 17 At a current density of 1651 mA/ cm 2 , we observe complete degradation of the BE-POLED, which manifests itself as a strong increase of current density and drop in the luminance (Figure 2b).…”

“…However, direct electrical excitation of polaritons is of great interest for work toward an electrically pumped organic polariton laser diode. While efficient electrical generation of polaritons at green and red wavelengths has been achieved (up to 10% external quantum efficiency (EQE)), , the development of efficient and bright devices emitting blue light is particularly difficult (with current devices reaching no more than 0.1% EQE) due to the high singlet state energies involved, which can lead to molecular degradation and Joule heating. Irrespective of the color of emission, upon electrical excitation, the majority of the generated excitons have triplet character, which is a direct result of spin statistics.…”

High-Performance Vertical Light-Emitting Transistors Based on ZnO Transistor/Quantum-Dot Light-Emitting Diode Integration and Electron Injection Layer Modification

“…As the energy diagram shown in Figure 1b, CdSe/ZnS QD has relatively low HOMO and LUMO levels, thus requiring appropriate injection/transporting layers to improve electron-hole recombination. We used a 25 nm ZnO:PEI nanocomposite as the EIL deposited on the bottom ZnO transistor [27,28]. The ZnO:PEI nanocomposite was prepared by dissolving zinc acetylacetonate hydrate and PEI in ethanol at a controlled concentration, followed by spin-coating and annealing at 120 • C for 90 min in the ambient environment.…”

Donor-Acceptor Copolymers with 9-(2-Ethylhexyl)carbazole or Dibenzothiophene-5,5-dioxide Donor Units and 5,6-Difluorobenzo[c][1,2,5]thiadiazole Acceptor Units for Photonics

“…The CP2 inverted LEDs exhibited higher EL efficiency at low current densities than the CP2 regular LEDs. LEDs of the simple single-layer structure without any optimization were tested only, and therefore their efficiency could be further enhanced, for example, by the optimization of the active layer using polymer blends and/or the LED architecture optimization [91,[95][96][97][98][99][100]. The regular and inverted LEDs exhibited good performance with low onset voltages between 2 and 3 V. Examples of the current-voltage and EL intensity-voltage characteristics of LEDs are displayed in Figure 11.…”

“…The CP2 inverted LEDs exhibited higher EL efficiency at low current densities than the CP2 regular LEDs. LEDs of the simple single-layer structure without any optimization were tested only, and therefore their efficiency could be further enhanced, for example, by the optimization of the active layer using polymer blends and/or the LED architecture optimization [91,[95][96][97][98][99][100].…”