Design, preparation method and application of polarized white organic light emitting diode

Abstract

The application relates to a design, a preparation method and an application of a polarized white light organic light emitting diode, and belongs to the field of diodes. A distributed Bragg reflector is integrated into a green organic light emitting diode, the distributed Bragg reflector and a metal aluminum electrode of the organic light emitting diode form a Fabry-Perot resonant cavity, the organic light emitting diode is modulated to emit light, and through adjustment of the microcavity length of the device, the resonant cavity of excitons formed by light emitting material and the film is realized, strong coupling is generated, polarized sub-emission is formed, and the light emission is changed from green light emission into polarized white light emission. Single light emitting layer single-peak green light is converted into double-peak white light, the distributed Bragg reflector has high reflectivity in a forbidden band region, the quality of the Fabry-Perot resonant cavity formed by the distributed Bragg reflector and the aluminum electrode is guaranteed, the film thickness of each layer of the distributed Bragg reflector is controlled, the forbidden band position is controlled at a suitable position, and further polarized white light emission of strong coupling is realized.

Description

Technical Field

[0001] This invention relates to the design, fabrication method and application of a polarized white organic light-emitting diode, belonging to the field of organic light-emitting diode technology. Background Technology

[0002] White organic light-emitting diodes (OLEDs) are becoming a key technology for next-generation energy-efficient solid-state lighting and full-color flat panel displays. Efforts are focused on exploring functional materials, manipulating and distributing excitons, optimizing device configurations, and developing manufacturing technologies. Generally, the reported material design approaches can be divided into two main methods. The first involves vertically or horizontally stacking emitting layers to generate white light by mixing the light emitted independently by red, green, and blue OLEDs. While these strategies result in stable white emission, achieving the desired color balance becomes complex due to the need for precise control over the thickness and composition of each layer. The second approach involves constructing a single emitting layer, which is formed by a matrix material and multiple doped emitters. White light can be generated either through Dexter energy transfer or through bimolecular excited species (such as excimers and excitocomplexes).

[0003] Compared to the first strategy, single-emitter white organic light-emitting diodes (OLEDs) have gained commercial favor due to their significantly simplified device structure and reduced production costs. However, a major challenge lies in the rational control of singlet and triplet excitons within the single emitter layer, making the simultaneous improvement of efficiency and color control a fundamental problem for single-emitter white OLEDs. Another approach to realizing white OLEDs is through spectral reconstruction by introducing optical resonances. Typical optical resonators include plasmon resonators, Mie resonators, Fabry-Perot cavities, quantum crystal cavities, and hybrid cavities. These can generate strong light fields to enhance the interaction between light and matter, representing the building blocks of modern optoelectronics and leading to the realization of many transformative optical devices with the desired functionality. Introducing these resonators is a promising strategy for addressing challenges such as poor full-color tunability, limited polarization modulation, and long response times. In particular, when the light-matter interaction between the electromagnetic mode and electronic excitation of the cavity enters the strong region, new half-light, half-matter boson quasiparticles, called exciton-polarons, are usually generated, which become very important for controlling the coherence and delocalization properties of polarization levels and polarons. The corresponding organic light-emitting diode device is called a polaron organic light-emitting diode.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a design, fabrication method and application of a polarized white organic light-emitting diode (OLED) to achieve a high-efficiency, low or no angle dependence (white light at different emission angles) white OLED.

[0006] First, the photoluminescence and electroluminescence spectra of the luminescent layer were tested to further determine the exciton energy.

[0007] According to the Helmholtz equation, when the material inside the microcavity is fixed, whether the cavity membrane and excitons can resonate depends only on the cavity length. The derived formula determines the resonant range of the cavity length. Then, the organic light-emitting diode (OLED) is optimized to determine the optimal cavity length for its optical and electrical performance. Optical performance optimization is achieved through simulation calculations, adjusting the thickness of the electron transport layer. Because the refractive index of the electron transport layer is relatively high, its impact on optical performance is more significant than other layers, such as the hole transport layer. The optimal range for optical performance is obtained when the strongest electric field distribution inside the device is at the light-emitting layer. Electrical performance optimization is achieved by calculating the thickness range required to reach injection equilibrium using the carrier mobility of the material used. Taking all these factors into account, the optimal cavity length, i.e., the thickness of each thin film, is obtained. The cavity length refers to the sum of all dielectric thin films contained within the resonant cavity composed of the distributed Bragg reflector and the OLED metal cathode.

[0008] The present invention relates to a polarized white organic light-emitting diode, characterized in that a distributed Bragg reflector is deposited on a glass substrate, a tungsten-doped indium oxide anode thin film is deposited on the distributed Bragg reflector, a hole injection layer PEDOT:PSS is deposited on the tungsten-doped indium oxide anode thin film, a light-emitting layer is deposited on the hole injection layer PEDOT:PSS, and a hole blocking layer, an electron transport layer, a modification transition layer, and a metal cathode electrode layer are deposited sequentially on the light-emitting layer.

[0009] The distributed Bragg reflector uses alternating layers of tantalum pentoxide (high refractive index material) and silicon dioxide (low refractive index material). The tantalum pentoxide layers are all the same thickness, 56-60 nm; the silicon dioxide layers are all the same thickness, 81-85 nm.

[0010] The thickness of the tungsten-doped indium oxide anode film is 180 nm; the hole injection layer PEDOT:PSS film thickness is 30 nm. The light-emitting layer is composed of polyvinylcarbazole and host / guest materials, with CBD and BD-F being the host and guest materials, respectively. The mass ratio of polyvinylcarbazole to the host / guest materials is 1:3:1, and the light-emitting layer film thickness is 30 nm. The thicknesses of the hole blocking layer, electron transport layer, modification layer, and aluminum electrode layer are 10 / 70 / 1 / 130 nm, respectively.

[0011] The method for fabricating the polarized white organic light-emitting diode of the present invention is as follows:

[0012] Step 1: Deposit a distributed Bragg reflector on the prepared glass substrate using an electron beam evaporation device. The distributed Bragg reflector uses alternating layers of tantalum pentoxide (high refractive index material) and silicon dioxide (low refractive index material).

[0013] Step 2: Place the substrate obtained in Step 1 into a vacuum thermal evaporation equipment to deposit an anode thin film doped with indium tungsten oxide.

[0014] Step 3: Drop-coat the hole injection layer PEDOT:PSS onto the substrate obtained in Step 2, anneal it, and cool it to room temperature.

[0015] Step 4: Accurately weigh the polyvinylcarbazole and the host and guest materials of the luminescent layer according to a certain ratio, put them into a glass bottle and transfer them into a glove box. Add a certain amount of solvent chlorobenzene to the glove box to dissolve them, and place it on a heating table for heating.

[0016] Step 5: Transfer the substrate obtained in step 3 into a glove box, spin-coat the solution obtained in step 4, anneal, and then cool to room temperature.

[0017] Step 6: If multiple polarized white organic light-emitting diode arrays can be fabricated at once, then the light-emitting layer around each polarized white organic light-emitting diode is removed to expose the corresponding anode.

[0018] Step 7: After the light-emitting layer is prepared, it is transferred into a vacuum thermal evaporation equipment to sequentially deposit a hole blocking layer, an electron transport layer, a modification transition layer, and a metal cathode electrode layer, thus obtaining a polarized white organic light-emitting diode.

[0019] In step 1 of the above invention, the glass substrate is first immersed in deionized water with added detergent. The surface of the glass substrate is then wiped with cotton swabs held by tweezers. Subsequently, it is ultrasonically treated twice each with deionized water, acetone, and ethanol, with each ultrasonic treatment lasting 20 minutes. When using electron beam evaporation to deposit a distributed Bragg reflector, the vacuum level is below 3*10... -4 Evaporation was performed under Pa conditions, with the evaporation rate controlled at [value missing]. In a distributed Bragg reflector, the silicon dioxide layer has the same thickness, the tantalum pentoxide layer has the same thickness, and the silicon dioxide layer and the tantalum pentoxide layer have different thicknesses.

[0020] In step 2 of the above invention, when using vacuum thermal evaporation, the vacuum level is below 3*10 -4 Evaporation was performed under Pa conditions, with the evaporation rate controlled at [value missing]. The thickness is controlled at around 180 nanometers.

[0021] In step 3 of the above invention, the doping ratio of polyvinylcarbazole and the host-guest material of the luminescent layer is 1mg:3mg:1mg, and the volume of the solvent chlorobenzene is 0.5ml. The heating time on the heating stage is more than 6 hours, and the temperature is 60°C.

[0022] In step 4 of the above invention, the drop coating speed is 2900 rpm and the time is 40 seconds; after the drop coating is completed, annealing is performed for 15 minutes at a temperature of 160°C. After annealing, the substrate is quickly transferred to a glove box and cooled to room temperature before subsequent operations are performed. The film thickness is 30 nanometers.

[0023] In step 5 of the above invention, the light-emitting layer is prepared by spin coating at a speed of 3000 rpm for 60 seconds. After spin coating, annealing is performed for 30 minutes at a temperature of 60°C, and the film thickness is 30 nanometers.

[0024] In step 6 of the above invention, a scraper is used to remove the thin film around each polarized white organic light-emitting diode up to the anode position, so that each polarized white organic light-emitting diode has an independent anode thin film.

[0025] In step 7 of the above invention, when using vacuum thermal evaporation, the evaporation is performed under a vacuum level lower than 3*10-4 Pa, and the evaporation rate is controlled at... The hole blocking layer, electron transport layer, modification layer, and aluminum electrode layer have thicknesses of 10 / 70 / 1 / 130 nanometers, respectively.

[0026] This invention integrates a distributed Bragg reflector into an organic light-emitting diode (OLED). The distributed Bragg reflector and the aluminum electrode of the OLED form a Fabry-Pérot cavity, modulating the OLED's emission. By adjusting the cavity length, excitons formed by the luminescent material resonate with the cavity film, generating strong coupling and polaron emission, thus transforming green light emission into polaron white light emission. In this invention, strong coupling converts single-peak green light from a single emitting layer into double-peak white light. The designed distributed Bragg reflector has high reflectivity in its bandgap region, ensuring the quality of the Fabry-Pérot cavity formed with the aluminum electrode. By controlling the thickness of each layer of the distributed Bragg reflector, the bandgap position is controlled at a suitable location, further achieving strongly coupled polaron white light emission.

[0027] This invention integrates a distributed Bragg reflector into a green organic light-emitting diode (OLED), creating strong coupling and polaron emission. This transforms a single-emitting-layer green OLED into a polarized white OLED. The resulting polarized white OLED achieves an external quantum efficiency of 4.52% and a Rabi splitting energy as high as 511 meV, exhibiting polaron emission and a reduced divergence angle from 70° to 50°. Furthermore, it emits white light at all angles, demonstrating low angle dependence. The fabricated polarized white OLED shows promising applications in displays and lighting. Attached Figure Description

[0028] The accompanying drawings, as part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention, but do not constitute an undue limitation of the invention. Obviously, the drawings described below are merely some embodiments, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings:

[0029] Figure 1 This is a schematic diagram of the structure of a green organic light-emitting diode and a polarized white organic light-emitting diode;

[0030] Figure 2 This is a schematic diagram of a distributed Bragg reflector structure.

[0031] Figure 3 This is an atomic force microscope image of a tungsten-doped indium oxide substrate. Surface roughness is characterized by RMS.

[0032] Figure 4 These are images obtained using an atomic force microscope with a distributed Bragg reflector and an indium tungsten oxide substrate. Surface roughness is characterized by RMS.

[0033] Figure 5 This is a comparison chart of experimental and simulated results of the reflectivity of a distributed Bragg reflector and a tungsten-doped indium oxide substrate.

[0034] Figure 6 This is the positive emission spectrum of a green organic light-emitting diode and a polarized white organic light-emitting diode.

[0035] Figure 7 This is an external quantum efficiency-luminance curve for green organic light-emitting diodes and polarized white organic light-emitting diodes.

[0036] Figure 8 These are the color coordinates and corresponding physical images of green organic light-emitting diodes (OLEDs) and polarized white organic light-emitting diodes (OLEDs). (The color coordinates are calculated from the spectral diagrams.)

[0037] Figure 9 , where represents the electroluminescence spectrum and corresponding color coordinates at different emission angles in Experiment Example 1.

[0038] (Where 0° represents positive emission) Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0040] Example 1

[0041] The prepared glass substrate is transferred to an electron beam evaporation apparatus, where a vacuum of 3*10⁻⁶ is applied. -4 Depositing a distributed Bragg reflector under Pa conditions involves first depositing tantalum pentoxide on a glass substrate at a deposition rate of [missing information]. Around [percentage missing]. After cooling, silicon dioxide deposition continues, with a deposition rate of [percentage missing]. The deposition process is repeated until a distributed Bragg reflector with a period of 5 is formed, for a total of 10 layers. The structure consists of alternating thin films of tantalum pentoxide and silicon dioxide, 5 layers each, with thicknesses of 85 / 60 nm for silicon dioxide and tantalum pentoxide, respectively. After cooling to room temperature, it is removed and placed in a vacuum thermal evaporation apparatus at a vacuum level of 3*10 nm. -4 Under the condition of Pa, the deposition electrode is tungsten-doped indium oxide, and the deposition rate is [missing value].

[0042] Accurately weigh 1 mg of polyvinylcarbazole, 3 mg of the main material CBP, and 1 mg of the guest luminescent material BD-F using a 1 / 10,000 analytical balance and place them in the same glass bottle. Gently loosen the bottle cap and transfer it into a glove box. Add 0.5 ml of chlorobenzene solution to dissolve the luminescent material. Place the glass bottle on a heating table at 60°C for more than 6 hours to ensure complete dissolution. Then, prepare the spin-coating solution for the luminescent layer.

[0043] A PEDOT:PSS hole injection layer was drop-coated onto a substrate containing a distributed Bragg reflector and indium tungsten oxide. After drop-coating, the substrate was annealed at 160°C for 15 minutes and immediately transferred to a glove box to cool to room temperature. A light-emitting layer was prepared using a solution method, with 26 μL of solution spin-coated at 3000 rpm for 60 seconds. The annealed substrate was then annealed at 60°C for 30 minutes. After cooling to room temperature, the solution-prepared film was removed using a doctor blade, particularly at the anode-covered area, and then transferred to a vapor deposition chamber. The vapor deposition was carried out under a vacuum of 3*10⁻⁶. -4Under the condition of Pa, a hole blocking layer (DPEPO), an electron transport layer (TmPyPb), a modification layer (LiF), and an aluminum cathode electrode layer are deposited sequentially, with the organic material evaporation rate controlled at [value missing]. The LiF evaporation rate is controlled at approximately [value missing]. The electrode aluminum evaporation rate is controlled at approximately [value missing]. about.

[0044] Example 2

[0045] The prepared glass substrate is transferred to an electron beam evaporation apparatus, where a vacuum of 3*10⁻⁶ is applied. -4 Depositing a distributed Bragg reflector under Pa conditions involves first depositing tantalum pentoxide on a glass substrate at a deposition rate of [missing information]. Around [percentage missing]. After cooling, silicon dioxide deposition continues, with a deposition rate of [percentage missing]. The deposition process was repeated until a distributed Bragg reflector with a period of 5 was formed, for a total of 10 layers. The structure consisted of alternating thin films of tantalum pentoxide and silicon dioxide, five layers each, with thicknesses of 81 and 56 nm for silicon dioxide and tantalum pentoxide, respectively. After cooling to room temperature, the material was removed and placed in a vacuum thermal evaporation apparatus at a vacuum level of 3*10⁻⁶. -4 Under the condition of Pa, the deposition electrode is tungsten-doped indium oxide, and the deposition rate is [missing value].

[0046] Accurately weigh 1 mg of polyvinylcarbazole, 3 mg of the main material CBP, and 1 mg of the guest luminescent material BD-F using a 1 / 10,000 analytical balance and place them in the same glass bottle. Gently loosen the bottle cap and transfer it into a glove box. Add 0.5 ml of chlorobenzene solution to dissolve the luminescent material. Place the glass bottle on a heating table at 60°C for more than 6 hours to ensure complete dissolution. Then, prepare the spin-coating solution for the luminescent layer.

[0047] A PEDOT:PSS hole injection layer was drop-coated onto a substrate containing a distributed Bragg reflector and indium tungsten oxide. After drop-coating, the substrate was annealed at 160°C for 15 minutes and immediately transferred to a glove box to cool to room temperature. A light-emitting layer was prepared using a solution method, with 26 μL of solution spin-coated at 3000 rpm for 60 seconds. The annealed substrate was then annealed at 60°C for 30 minutes. After cooling to room temperature, the solution-prepared film was removed using a doctor blade, particularly at the anode-covered area, and then transferred to a vapor deposition chamber. The vapor deposition was carried out under a vacuum of 3*10⁻⁶. -4 Under the condition of Pa, a hole blocking layer (DPEPO), an electron transport layer (TmPyPb), a modification layer (LiF), and an aluminum cathode electrode layer are deposited sequentially, with the organic material evaporation rate controlled at [value missing]. The LiF evaporation rate is controlled at approximately [value missing]. The electrode aluminum evaporation rate is controlled at approximately [value missing]. about.

[0048] By introducing a distributed Bragg reflector structure into an organic light-emitting diode (OLED), a single-emitting-layer green OLED was transformed into a polarized white OLED. Optimized cavity length calculations achieved strong coupling, resulting in polaron emission. The divergence angle was reduced from 70° to 50°, and the turn-on voltage decreased from 5.0V to 4.6V. Calculations showed a Rabi splitting energy as high as 511 meV, confirming the strong coupling and polaron emission. The forward emission spectra of the green and polarized white OLEDs were tested, and the corresponding color coordinates were calculated. Physical images of the devices were provided, providing a more intuitive demonstration of the transformation from green to polarized white emission. By testing the emission spectra of the polarized white OLED at different angles and calculating the corresponding color coordinates, it was found that the color coordinates were within the white light range at all emission angles, achieving white light emission at all angles. The device performance of the green and polarized white OLEDs, specifically the external quantum efficiency versus brightness curves, were tested, resulting in a polarized white OLED with an external quantum efficiency of up to 4.52%.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A polarized white organic light-emitting diode, characterized in that, A distributed Bragg reflector is deposited on a glass substrate. A tungsten-doped indium oxide anode film is deposited on the distributed Bragg reflector. A hole injection layer PEDOT:PSS is deposited on the tungsten-doped indium oxide anode film. A light-emitting layer is deposited on the hole injection layer PEDOT:PSS. A hole blocking layer, an electron transport layer, a modification transition layer, and a metallic aluminum cathode electrode layer are deposited sequentially on the light-emitting layer. The distributed Bragg reflector uses alternating layers of high-refractive-index tantalum pentoxide and low-refractive-index silicon dioxide for five cycles; the thickness of the tantalum pentoxide layers is the same, 56-60 nm; the thickness of the silicon dioxide layers is the same, 81-85 nm. The thickness of the tungsten-doped indium oxide anode film is 180 nm; the hole injection layer PEDOT:PSS film thickness is 30 nm; the light-emitting layer is composed of polyvinylcarbazole and light-emitting layer host and guest materials, with the host material and guest material being CBD and BD-F, respectively; the mass ratio of polyvinylcarbazole to light-emitting layer host and guest materials is 1:3:1, and the thickness of the light-emitting layer film is 30 nm; the thicknesses of the hole blocking layer, electron transport layer, modification transition layer, and aluminum cathode electrode layer are 10, 70, 1, and 130 nm, respectively; A distributed Bragg reflector was integrated into an organic light-emitting diode (OLED) to form a Fabry-Pérot cavity with the aluminum electrode of the OLED. The designed distributed Bragg reflector has high reflectivity in its bandgap region, ensuring the quality of the Fabry-Pérot cavity. By controlling the thickness of each layer of the distributed Bragg reflector, the bandgap position is controlled at an appropriate location to modulate the light emission of the OLED. By adjusting the cavity length, the excitons resonate with the cavity film, generating strong coupling. This transforms the single-peak green light emission from a single-emitting layer into a double-peak white light emission from polaritons. The resulting white OLED achieves an external quantum efficiency of 4.52% and a Rabi splitting energy of 511 meV at its best performance. The divergence angle is reduced from 70° to 50°, and the light is white at all angles, exhibiting low angle dependence.

2. The method for fabricating a polarized white organic light-emitting diode according to claim 1, characterized in that, Includes the following steps: Step 1: Deposit a distributed Bragg reflector on the prepared glass substrate using an electron beam evaporation device. The distributed Bragg reflector is made by alternating layers of high refractive index material tantalum pentoxide and low refractive index material silicon dioxide. Step 2: Place the substrate obtained in Step 1 into a vacuum thermal evaporation equipment to deposit a tungsten-doped indium oxide anode thin film; Step 3: Drop-coat the hole injection layer PEDOT:PSS onto the substrate obtained in Step 2, anneal it, and cool it to room temperature; Step 4: Accurately weigh the polyvinylcarbazole and the host and guest materials of the luminescent layer according to a certain ratio, put them into a glass bottle and transfer them into a glove box. Add a certain amount of solvent chlorobenzene to the glove box to dissolve them, and place it on a heating table for heating. Step 5: Transfer the substrate obtained in step 3 into a glove box, spin-coat the solution obtained in step 4, anneal, and then cool to room temperature; Step 6: Multiple polarized white organic light-emitting diode arrays can be fabricated at once. The thin film covering the anode region formed by spin coating and annealing is removed to expose the anode. Step 7: After the light-emitting layer is prepared, it is transferred into a vacuum thermal evaporation equipment to sequentially deposit a hole blocking layer, an electron transport layer, a modification transition layer, and a metal aluminum cathode electrode layer, thus obtaining a polarized white organic light-emitting diode.

3. The method according to claim 2, characterized in that, In step 1, the glass substrate is first immersed in deionized water with added detergent. The surface of the glass substrate is then wiped with cotton swabs held by tweezers. Subsequently, it is ultrasonically treated twice each with deionized water, acetone, and ethanol, with each ultrasonic treatment lasting 20 minutes. When using electron beam evaporation to deposit a distributed Bragg reflector, the vacuum level is below 3*10⁻⁶. -4 Evaporation was carried out under Pa conditions, with the evaporation rate controlled at 1-2 Å / S; in the distributed Bragg reflector, the silicon dioxide layer and the tantalum pentoxide layer had the same thickness, while the silicon dioxide layer and the tantalum pentoxide layer had different thicknesses.

4. The method according to claim 2, characterized in that, In step 2, when using vacuum thermal evaporation, the vacuum level is below 3*10. -4 Evaporation was carried out under Pa conditions, with the evaporation rate controlled at around 1.5 Å / S; In step 3, the drop coating speed is 2900 rpm and the time is 40 seconds; after the drop coating is completed, annealing is performed for 15 minutes at a temperature of 160°C. After annealing, the substrate is quickly transferred to a glove box and cooled to room temperature. In step 4, the doping ratio of polyvinylcarbazole and the host-guest material of the luminescent layer is 1 mg: 3 mg: 1 mg, and the volume of chlorobenzene solvent corresponding to each mg of polyvinylcarbazole is 0.5 ml; the heating time on the heating stage is more than 6 hours and the temperature is 60℃. In step 5, the light-emitting layer is prepared by spin coating at 3000 rpm for 60 seconds. After spin coating, annealing is performed for 30 minutes at 60°C. In step 6, a scraper is used to remove the thin film around each polarized white organic light-emitting diode up to the anode position, so that each polarized white organic light-emitting diode has an independent anode film. In step 7, when using vacuum thermal evaporation, the vacuum level is below 3*10. -4 Evaporation was carried out under Pa conditions, with the evaporation rate controlled between 0 and 5 Å / s and not equal to 0, to deposit hole blocking layers, electron transport layers, modification transition layers, and aluminum cathode electrode layers, respectively.

5. The application of the polarized white organic light-emitting diode as described in claim 1, in the fields of display and lighting.

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