Method and program for fabricating a current-injection organic semiconductor laser diode

Abstract

To provide an electrically driven organic semiconductor laser diode (OSLD).SOLUTION: A current injection organic semiconductor laser diode is disclosed that includes a pair of electrodes, an optical resonator structure, and one or more organic layers including an optical amplifying layer containing organic semiconductors, and has sufficient overlap of the exciton density distribution during current injection and the electric field intensity distribution of the resonant optical mode to emit laser light.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a current-injection organic semiconductor laser diode and a method for fabricating the same. The present invention also relates to a program for designing a current-injection organic semiconductor laser diode. [Background technology]

[0002] The properties of optically pumped organic semiconductor lasers (OSLs) have improved significantly over the past 20 years, as a result of major advances in both the development of high-gain organic semiconductor materials and the design of high-Q-factor resonator structures. 1-5 The advantages of organic semiconductors as laser gain media include their high photoluminescence (PL) quantum yield, large stimulated emission cross-section, and broad emission spectrum across the entire visible region, along with their chemically tunable and easy-to-process properties. Recent advances in low-threshold distributed feedback (DFB) OSLs have demonstrated optical pumping with electrically driven nanosecond pulsed inorganic light-emitting diodes, paving the way for new, compact, and low-cost visible laser technologies. 6 However, the ultimate goal is the electrically driven organic semiconductor laser diode (OSLD). The realization of OSLDs will enable the complete integration of organic photonics and optoelectronic circuits, and will open up new applications in spectroscopy, display devices, medical devices (such as retinal displays, sensors, and photodynamic therapy devices), and LIFI telecommunications.

[0003] The main obstacles to realizing laser oscillation by direct electric pumping of organic semiconductors are optical losses from electrical contacts and triplet and polaron losses that occur at high current densities. 4,5,7-9 To solve these fundamental loss problems, proposed methods include the use of triplet quenchers to suppress triplet absorption loss and singlet disappearance due to singlet-triplet exciton annihilation. 10-12 Furthermore, spatially separating the locations where exciton formation and exciton emission decay occur, thereby minimizing the polaron disappearance process and reducing the device active region. 13 There are advancements in organic light-emitting diodes (OLEDs) and photo-pumped organic semiconductor DFB lasers. 5Current-injected OSLD has not yet been fully demonstrated.

[0004] Patent Document 1 P1 This document describes the realization of a current-injection OSLD. According to the literature, the device is fabricated by forming a diffraction grating (resonator) with a pitch of 500 nm on an ITO film, then forming a 250 nm thick hole transport layer of N,N-diphenyl-N,N',-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) by vapor deposition, further forming a 100 nm thick radiation layer by spin-coating a dichloromethane solution of aromatic polycarbonate resin, forming a 250 nm thick electron transport layer of 2-(4-tertiary-butylphenyl)-5-(4-biphenylyl)-l,3,4-oxadiazole by vapor deposition, and finally forming a 200 mm thick MgAg alloy layer. This document describes laser emission by applying a voltage of 30 V to this device. However, in practice, when the dichloromethane solution of polycarbonate was applied to the TPD layer by spin-coating, the TPD layer dissolved, and therefore the device could not be reproduced. Furthermore, this device has an organic hole transport layer and an organic electron transport layer, each 250 nm thick, in addition to a 100 nm thick organic light-emitting layer, and therefore the total thickness of the organic layer is quite large. Laser oscillation cannot be obtained by applying a 30 V DC to a device containing such a large total thickness of organic layer.

[0005] Other quarantine P2,P3 These documents discuss the possibility of realizing current-injection OSLDs. However, these patent documents only provide a general description of current-injection OSLDs and do not show any specific current-injection OSLDs that have confirmed laser oscillation. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2004-186599 [Patent Document 2] Japanese Patent Publication No. Heisei 10-321941 [License 3] Japanese Patent Publication No. 2008-524870 [Non-licensed literature]

[0007] [Non-licensed Document 1] Tessler, N., Denton, GJ & Friend, RH Lasing from conjugated-polymer microcavities. Nature 382,​​ 695-697 (1996). [Non-licensed Document 2] Kozlov, VG, Bulovic, V., Burrows, PE & Forrest, SR Laser action in organic semiconductor waveguide and double-heterostructure devices. Nature 389, 362-364 (1997). [Non-licensed Document 3] Hide, F. et al. Semiconducting polymers: A new class of solid-state laser materials. Science 273, 1833 (1996). [Non-licensed Document 4] Samuel, IDW & Turnbull, GA Organic semiconductor lasers. Chem. Rev. 107, 1272-1295 (2007). [Non-licensed Document 5] Kuehne, AJC & Gather MC Organic lasers: Recent developments on materials, device geometries and fabrication techniques. Chem. Rev. 116, 12823-12864 (2016). [Non-licensed Document 6] Tsiminis, G. et al. Nanoimprinted organic semiconductor lasers pumped by a light-emitting diode. Adv. Mater. 25, 2826–2830 (2013).

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[0008] In that sense, a laser oscillation current injection OSLD has not yet been provided. The object of the present invention is to provide a laser oscillation current injection OSLD. As a result of diligent research, the inventors have found that the present invention can achieve this object. The present invention provides a current injection organic semiconductor laser diode comprising a pair of electrodes, an optical resonator structure, and one or more organic layers including an optical amplification layer made of an organic semiconductor, which satisfies at least one of the following "2" to "16" and / or may have at least one embodiment as described below. The present invention includes the following embodiments.

[0009] 1.1 A current-injection organic semiconductor laser diode comprising a pair of electrodes, an optical resonator structure, and one or more organic layers including an optical amplification layer containing an organic semiconductor, wherein there is sufficient overlap between the exciton density distribution and the electric field intensity distribution of the resonant optical mode during current injection to emit laser light.

[0010] 2. A current-injection organic semiconductor laser diode according to item 1, wherein the optical resonator structure has a distributed feedback (DFB) structure.

[0011] 3. A current-injection organic semiconductor laser diode according to item 2, wherein the optical resonator structure consists of a secondary Bragg scattering region surrounded by a primary Bragg scattering region.

[0012] 4. A current-injection organic semiconductor laser diode according to item 2, wherein secondary Bragg scattering regions and primary Bragg scattering regions are alternately formed in an optical resonator structure.

[0013] 5. A current-injection organic semiconductor laser diode according to any of items 1 to 4, wherein the number of organic layers is 2 or less.

[0014] 6. A current-injection organic semiconductor laser diode according to any of items 1 to 5, wherein the thickness of the optical amplification layer is greater than 50% of the total thickness of one or more organic layers.

[0015] 7. A current-injection organic semiconductor laser diode according to any of items 1 to 6, wherein the organic semiconductor contained in the optical amplification layer is amorphous.

[0016] 8. A current-injection organic semiconductor laser diode according to any of items 1 to 7, wherein the molecular weight of the organic semiconductor contained in the photoamplification layer is 1000 or less.

[0017] 9. A current-injection organic semiconductor laser diode according to any of items 1 to 8, wherein the organic semiconductor contained in the optical amplification layer is nonpolymeric.

[0018] 10. A current-injection organic semiconductor laser diode according to any one of items 1 to 9, wherein the organic semiconductor contained in the optical amplification layer has at least one stilbene unit.

[0019] 11. A current-injection organic semiconductor laser diode according to any one of items 1 to 10, wherein the organic semiconductor contained in the optical amplification layer has at least one carbazole unit.

[0020] 12. A current-injection organic semiconductor laser diode according to any of items 1 to 11, wherein the organic semiconductor contained in the optical amplification layer is 4,4'-bis[(N-carbazole)styryl]biphenyl (BSBCz).

[0021] 13. A current-injection organic semiconductor laser diode according to any of items 1 to 12, having an electron injection layer as one of the organic layers.

[0022] 14. A current-injection organic semiconductor laser diode according to item 13, wherein the electron injection layer contains Cs.

[0023] 15. A current-injection organic semiconductor laser diode according to any of items 1 to 14, having a hole injection layer as an inorganic layer.

[0024] 16. A current-injection organic semiconductor laser diode according to item 15, wherein the hole injection layer contains molybdenum oxide.

[0025] 17. A method for designing a current-injection organic semiconductor laser diode, A method comprising the step of selecting a diode material and designing its structure to maximize the overlap between the exciton density distribution and the electric field intensity distribution of the resonant optical mode during current injection.

[0026] 18. A method for fabricating an organic semiconductor laser diode with current injection, A step of evaluating the overlap between the exciton density distribution and the electric field intensity distribution of the resonant optical mode during current injection in a designed or existing diode, The steps include designing a new diode by changing at least one of the diode's materials and structure to increase the overlap between the exciton density distribution during current injection and the electric field intensity distribution of the resonant optical mode, A method including the steps of creating a new diode.

[0027] 19. A current-injection organic semiconductor laser diode prepared by the method of Section 18.

[0028] 20. A program for designing a current-injection organic semiconductor laser diode that maximizes the overlap between the exciton density distribution and the electric field intensity distribution of the resonant optical mode during current injection. [Brief explanation of the drawing]

[0029] [Figure 1]This figure shows the structure of an organic semiconductor DFB laser diode. a) A schematic diagram of the organic laser diode. b) and c) Laser microscope (b) and SEM (c) images of the DFB SiO2 diffraction grating structure fabricated on ITO at 5,000x and 200,000x magnification (inset). d) Cross-sectional SEM image of a complete OSLD. e) Cross-sectional EDX image of an OSLD. Contrast was increased to improve the visibility of low concentrations of Cs. [Figure 2] This figure shows the manufacturing and structure of OSLDs. a. Schematic diagram of the OSLD manufacturing process. b. Structure of the ITO-coated glass substrate used in this study, along with the general structure of the DFB diffraction grating. Detailed values ​​of various diffraction grating parameters can be seen in Table 1. c,d. EDX and SEM analysis of mixed-order DFB diffraction gratings created on ITO. These images show the possibility of achieving electrical contact with ITO. [Figure 3] This figure shows the electrical properties of an electro-pumped organic semiconductor DFB laser. a) Energy level diagram of an OSLD with the highest occupied molecular orbital and lowest empty molecular orbital levels shown with respect to the work functions of organic and inorganic materials. b) Micrographs of an OSLD and a reference OLED under DC operating conditions at 3.0 V. The lengths of the primary and secondary diffraction grating regions are 1.68 and 1.12 μm, respectively. c, d) Current density voltage (JV) characteristics (c) and ηEQE-J characteristics (d) of an OLED and OSLD under pulsed operation conditions (pulse width 400 ns and repetition rate 1 kHz). [Figure 4] This figure illustrates hole and electron transport in an organic layer. a and b show the structures of a hole-only device (a) and an electron-only device (b) used to evaluate transport, and c shows typical current density-voltage (JV) characteristics of the hole-only device (HOD) and electron-only device (EOD) under DC operation (filled symbols) and pulsed operation (outline symbols) conditions, using logarithmic and linear (inset) scales. The device area is 200x200μm. These JV curves demonstrate good hole and electron transport in the high-voltage region of the laser diodes fabricated in this study. At low voltages, electrons outnumber holes due to the trapping limitation of the hole current. [Figure 5]This figure shows the characteristics of OSLDs with various DFB shapes. a) Micrograph of an OSLD under DC operating conditions of 3.0V. The micrographs were taken at the same magnification, with all diffraction gratings extended vertically. b)c)d) Current density-voltage (JV) and ηEQE-J characteristics of the OSLD. e) Electroluminescence intensity and FWHM as a function of J. f) Emission spectrum collected perpendicular to the substrate plane as a function of J. [Figure 6] This figure shows the DC characteristics and emission spectra of the devices. a and b are the current density-voltage (JV) curves (a) and ηEQE-J curve (b) of the OLED and OSLD measured under DC operating conditions, and c is the PL spectrum of a neat BSBCz thin film (black line) and the EL spectra of the OLED (red line) and OSLD below the laser oscillation threshold (blue line). [Figure 7] This figure shows the laser oscillation characteristics of an OSLD. a) Emission spectra of the OSLD collected perpendicular to the substrate plane at various injection current densities. At current densities higher than 3.5 kA cm⁻², background EL increases significantly with respect to laser oscillation due to severe device degradation at the laser oscillation wavelength. b) Emission spectrum near the laser oscillation threshold, c) Output intensity and FWHM as a function of current, d) Output power as a function of current. The inset is a photograph of the OSLD under pulsed operation conditions at 50 V. [Figure 8] This figure shows the characterization of radiation from an OSLD. a. Emission spectra of the OSLD above the threshold measured at various polarization angles. Polarization is stronger above the threshold (inset, circle) than below the threshold (inset, triangle). Here, 90° corresponds to the direction parallel to the grooves of the DFB diffraction grating. b, c. CCD camera images (b) and cross-sections (c) showing the spatial Gaussian profile of the focused radiation beam from the OSLD at various current densities. d, e. Figures of the unfocused beam of the OSLD operating above the threshold projected onto the screen. [Figure 9]The characteristics of OSLD under optical pumping conditions are shown in Figures 8b and 8c, illustrating the test environment used to measure the beam profile. b. Characteristics, near-field beam image, and cross-section of OSLD (structure shown in Table 1) under optical excitation conditions below the threshold (ii), near the threshold (i), and above the threshold (iii). c. Characteristics, near-field beam image, and cross-section of OSLD-6 (structure shown in Table 1) under optical excitation conditions below the threshold (iv), near the threshold (v), and above the threshold (v). d. Far-field beam cross-sections of OSLD under optical excitation conditions above the threshold, near the threshold, and below the threshold, along with a simulated far-field beam above the threshold. The inset above the threshold shows the original emission pattern. e. Emission spectra of OSLD-6 collected perpendicular to the substrate plane under optical pumping conditions with various optical excitation densities. The steady-state photoluminescence spectrum of BSBCz on SiO2 with a diffraction grating is shown as a dotted line. f. Output intensity and FWHM of OSLD-6 as a function of optical excitation density. Excitation was performed for 3.0 ns using a 337 nm nitrogen laser, and the device was at ambient temperature. The slope efficiencies of g, h, i, optically pumped OSL (g, see Table 1 for structure), electrically pumped OSLD (h), and optically pumped OSLD-6 (i) are shown. The input power to the optically pumped devices was the power supply power, incident on the organic thin film side for OSL and on the glass side for OSLD-6. [Figure 10] This figure shows the triplet and radical cation and anion absorption spectra of BSBCz. a. Stimulated emission and triplet absorption cross-sectional spectra of BSBCz. The emission spectrum of the OSL was measured from a neat BSBCz thin film above the threshold. b. To investigate the spectral overlap between components, absorption spectra were measured for a neat BSBCz thin film (50 nm, black) and composite thin films BSBCz:MoO3 and BSBCz:Cs (molar ratio 1:1, 50 nm; blue and red). Absorption spectra were measured using an absorption spectrometer (Lamda 950, PerkinElmer). To show that the polaron absorption of the BSBCz OSLD is minimal, the steady-state PL spectrum of the neat BSBCz thin film (green) and a representative laser emission spectrum from the OSL under photo-pumping conditions (orange) are also shown. [Figure 11] This is an optical and electrical simulation, showing a) experimental (symbol) and simulated (solid line) JV curves for hole-only devices (blue circles), electron-only devices (red squares), and bipolar devices (black triangles). Model parameters were extracted from Figure 4 by fitting to a unipolar device, and these parameters were used to simulate the bipolar device. b) A comparison of the mobility calculated using the parameters extracted from the unipolar device (solid line) with the reported mobility (symbol) for holes (blue) and electrons (red) in BSBCz. c) Experimental (symbol) and simulated (solid line) JV curves for OSLD. d) A schematic diagram of the OSLD structure used in the calculations, e) the spatial distribution of the OSLD recombination rate profile R at J=500mA cm-2, f) a cross-section of the DFB device at y=0.11μm through (e), and g) the average exciton density as a function of current density for OSLD and OLED. [Figure 12] This figure shows a simulation of an OSLD. a) Spatial distribution of exciton density S. b) Electric field distribution of the passive DFB resonant cavity at the resonant wavelength λ0 = 483 nm for a structure extended to include the first-order region. c) Mode gain as a function of current density. d) Spatial overlap between the exciton density S(x,y) and the optical mode |E(x,y)|2 in the second-order region at J = -500 A cm⁻². Layers other than the diffraction grating are modeled to be flat (see Figure 11d), and y=0 corresponds to the BSBCZ / MoO3 interface. [Modes for carrying out the invention]

[0030] The contents of the present invention will be described in detail below. Representative embodiments and components related to specific examples of the present invention will be described below, but the present invention is not limited to these embodiments and examples. In this specification, a numerical range represented by "X to Y" means a range that includes the numerical values ​​X and Y as the lower and upper limits, respectively.

[0031] All references and descriptions in PCT / JP2017 / 033366 are incorporated herein by reference.

[0032] The current-injection OSLD of the present invention comprises at least one pair of electrodes, an optical resonator structure, and one or more organic layers including an optical amplification layer made of an organic semiconductor. The current-injection OSLD of the present invention has a configuration in which the overlap between the exciton density distribution during current injection and the electric field intensity distribution of the resonant optical mode is sufficient to emit laser light. "A configuration in which the overlap between the exciton density distribution during current injection and the electric field intensity distribution of the resonant optical mode is sufficient to emit laser light" means a configuration that enables laser oscillation and refers to the selection and combination of materials and structures described later.

[0033] The configuration and features of the present invention are described in detail below.

[0034] (Optical amplification layer) The photo-amplifying layer constituting the current-injection OSLD of the present invention comprises an organic semiconductor compound that contains carbon atoms but not metal atoms. The organic semiconductor compound preferably consists of one or more atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms, sulfur atoms, phosphorus atoms, and boron atoms. For example, an organic semiconductor compound consisting of carbon atoms, hydrogen atoms, and nitrogen atoms may be mentioned. A preferred example of the organic semiconductor compound is a compound containing at least one of stilbene units and carbazole units, and a more preferred example is a compound containing both stilbene units and carbazole units. The stilbene units and carbazole units may or may not be substituted with substituents such as alkyl groups. The organic semiconductor compound is preferably a non-polymer without repeating units. Preferably, the molecular weight of the compound is 1000 or less, for example, 750 or less. The photo-amplifying layer may contain two or more types of organic semiconductor compounds, but it is preferable to contain only one type of organic semiconductor compound.

[0035] The organic semiconductor compound used in the present invention can be selected from laser gain organic semiconductor compounds that enable laser oscillation when used in the organic light emitting layer of a photoexcited organic semiconductor laser. One of the most preferred organic semiconductor compounds is 4,4'-bis[(N-carbazole)styryl]biphenyl (BSBCz) (chemical structure in Fig. 1a) 15 This is because of the low amplified spontaneous emission (ASE) threshold of the thin film (0.30 μJ cm under 800 ps pulse photoexcitation conditions) -2 ) 16 and the ability to withstand high current density injection of up to 2.8 kA cm under 5 μs pulse operation conditions of an OLED having a maximum electroluminescence (EL) external quantum efficiency (η EQE ) exceeding 2%, which is an excellent combination of optical and electrical properties. Furthermore, laser oscillation under high repetition rate of 80 MHz and long pulse photoexcitation conditions of 30 milliseconds has recently been demonstrated in a light-pumped BSBCz-based DFB laser -2 mainly because of the extremely low triplet absorption loss at the laser oscillation wavelength of the BSBCz thin film. Apart from BSBCz, for example, compounds having an ASE threshold of preferably 0.60 μJ cm or less, more preferably 0.50 μJ cm or less, and even more preferably 0.40 μJ cm or less when formed in the same thin film as in Ref. 16 and measured under 800 ps pulse photoexcitation conditions can also be used. Furthermore, compounds showing durability of preferably 1.5 kA cm or more, more preferably 2.0 kA cm or more, and even more preferably 2.5 kA cm or more when formed in the same device as in Ref. 13 and measured under 5 μs pulse operation conditions can also be used. 13 17 -2 -2 -2 -2 -2 -2 <​​​​​​​​​​​​​​​​The current-injection OSLD of the present invention may include an electron injection layer, a hole injection layer, and the like, in addition to the photo-amplifying layer. These may be organic layers or inorganic layers without organic materials. When the current-injection OSLD has two or more organic layers, it is preferable to have a laminate structure consisting only of organic layers with no non-organic layers in between. In this case, the multiple organic layers may contain the same organic compounds as those in the photo-amplifying layer. The performance of the current-injection OSLD tends to be higher as the number of heterointerfaces of the organic layers decreases; therefore, the number of organic layers is preferably three or less, more preferably two or less, and most preferably one. When the current-injection OSLD has two or more organic layers, the thickness of the photo-amplifying layer is preferably more than 50% of the total thickness of the organic layers, more preferably more than 60%, and even more preferably more than 70%. When the current-injection OSLD has two or more organic layers, the total thickness of the organic layers may be, for example, 100 nm or more, 120 nm or more, or 170 nm or more, and may be 370 nm or less, 320 nm or less, or 270 nm or less. The refractive indices of the electron injection layer and the hole injection layer are preferably smaller than the refractive index of the optical amplification layer.

[0038] If an electron injection layer is provided, it is constructed such that a material that facilitates electron injection into the optical amplification layer is present in the electron injection layer. If a hole injection layer is provided, it is constructed such that a material that facilitates hole injection into the optical amplification layer is present in the hole injection layer. These materials may be organic compounds or non-organic materials. For example, the non-organic material for the electron injection layer contains an alkali metal such as Cs, and its concentration in the electron injection layer containing the organic compound may be, for example, more than 1% by weight, 5% by weight or more, or 10% by weight or more, or 40% by weight or less, or 30% by weight or less. The thickness of the electron injection layer may be, for example, 3 nm or more, 10 nm or more, or 30 nm or more, or 100 nm or less, 80 nm or less, or 60 nm or less.

[0039] As one preferred embodiment of the present invention, a current-injection OSLD having an electron injection layer and an optical amplification layer as organic layers and a hole injection layer as an inorganic layer can be illustrated. The non-organic material constituting the hole injection layer includes metal oxides such as molybdenum oxide. The thickness of the hole injection layer may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 100 nm or less, 50 nm or less, or 20 nm or less.

[0040] (Optical resonator structure) The current-injection OSLD of the present invention has an optical resonator structure. The optical resonator structure may be a one-dimensional or two-dimensional resonator structure. Examples of the latter include a circulator resonator structure and a Whisper-Gallery type optical resonator structure. Distributed feedback (DFB) structures and distributed Bragg reflector (DBR) structures are also usable. In the case of DFB, a mixed-order DFB diffraction grating structure is preferably used. That is, preferably, a mixed structure of DFB diffraction grating structures with different orders relative to the laser emission wavelength can be used. Specific examples include an optical resonator structure consisting of a secondary Bragg scattering region surrounded by a primary Bragg scattering region, and a mixed structure in which secondary Bragg scattering regions and primary scattering regions are alternately formed. Details of preferred optical resonator structures can be found in the specific examples shown below. As an optical resonator structure, the current-injection OSLD may further include an external optical resonator structure.

[0041] For example, the optical resonator structure may preferably be formed on an electrode. The material constituting the optical resonator structure includes an insulating material such as SiO2. For example, a diffraction grating structure may be formed, and the depth of the diffraction grating is preferably 75 nm or less, and more preferably selected from the range of 10 to 75 nm. The depth may be, for example, 40 nm or more, or less than 40 nm.

[0042] (electrode) The current-injection OSLD of the present invention has a pair of electrodes. For optical output, one of the electrodes is preferably transparent. With respect to the electrodes, electrode materials commonly used in the art can be appropriately selected considering their work function and other factors. Preferred electrode materials include, but are not limited to, Ag, Al, Au, Cu, ITO, etc.

[0043] (Preferred current injection OSLD) In a current-injection OSLD, excitons are generated by current excitation. The laser oscillation characteristics of a current-injection OSLD are improved by increasing the overlap between the distribution region of the generated exciton density and the field intensity distribution of the resonant optical mode. That is, when the exciton density overlaps with the optical resonant mode of the optical resonator structure, the laser oscillation characteristics can be improved. The exciton density distribution and the field intensity distribution of the resonant optical mode can be controlled by changing the structure and materials of the current-injection OSLD. For example, the distribution can be controlled by using a current-narrowing structure with a diffraction grating, and by controlling the depth and period of the diffraction grating. The distribution can also be controlled by specifying or controlling the material and thickness of the optical amplification layer, and in some cases the material and thickness of the electron injection layer and hole injection layer. Furthermore, more accurate dispersion control is possible by considering the conditions examined in the simulation calculations described later. A preferred current-injection OSLD has an overlap between the distribution of exciton density during current injection and the field intensity distribution of the resonant optical mode to a greater extent than the overlap in a specific current-injection OSLD shown later as an example of operation.

[0044] In the current-injected OSLD of the present invention, the ratio of electron mobility to hole mobility in the organic photogain layer is preferably controlled to be within the range of 1 / 10 to 10 / 1, more preferably 1 / 5 to 5 / 1, even more preferably 1 / 3 to 3 / 1, and even more preferably 1 / 2 to 2 / 1. By controlling this ratio to be within this range, the overlap between the exciton density distribution and the electric field intensity distribution of the resonant optical mode can be easily expanded.

[0045] In the current-injection OSLD of the present invention, preferably, the excitons generated by current excitation do not undergo substantial annihilation. The loss due to exciton annihilation is preferably less than 10%, more preferably less than 5%, even more preferably less than 1%, even more preferably less than 0.1%, even more preferably less than 0.01%, and most preferably 0%.

[0046] Preferably, the current-injected OSLD of the present invention exhibits substantially no polaron absorption loss at the laser oscillation wavelength. In other words, preferably, there is substantially no overlap between the polaron absorption spectrum and the emission spectrum of the organic semiconductor laser. The loss due to polaron absorption is preferably less than 10%, more preferably less than 5%, even more preferably less than 1%, even more preferably less than 0.1%, even more preferably less than 0.01%, and most preferably 0%.

[0047] The oscillation wavelength of the current-injected OSLD of the present invention preferably does not substantially overlap with the absorption wavelength region of the excited state, radical cation, or radical anion. This absorption may be caused by singlet-singlet, triplet-triplet, or polaron absorption. The loss due to absorption in the excited state is preferably less than 10%, more preferably less than 5%, even more preferably less than 1%, even more preferably less than 0.1%, even more preferably less than 0.01%, and most preferably 0%.

[0048] The current-injected OSLD of the present invention preferably lacks a triplet quenching agent.

[0049] (Method for creating a current-injection OSLD) The present invention also provides a method for fabricating a current-injection OSLD in which the OSLD is designed and fabricated so that the overlap between the exciton density distribution generated by current excitation and the electric field intensity distribution of the resonant optical mode can be increased. In the design, simulations are performed based on various conditions (e.g., the depth and period of the diffraction grating, the constituent materials and thicknesses of the optical amplification layer, electron injection layer and hole injection layer, etc.) to evaluate the overlap between the exciton density distribution and the electric field intensity distribution of the resonant optical mode. From the simulation results under various conditions, those evaluated as having a large overlap are selected that can be fabricated without problems, and these selected ones can be actually fabricated. Therefore, a current-injection OSLD with excellent laser oscillation characteristics can be efficiently provided.

[0050] In the above design, a pre-formed and usable design program for current-injection OSLDs can be created that has the function of designing to expand the overlap between the distribution of excitons generated by current excitation and the electric field strength distribution of the resonant optical mode. This program can be stored on a medium such as a hard disk or compact disk.

[0051] Furthermore, the present invention provides a method for improving the laser oscillation characteristics of a pre-designed or existing current-injection OSLD. The overlap between the exciton density distribution and the electric field intensity distribution of the resonant optical mode of a pre-designed or existing current-injection OSLD is evaluated by simulation calculations, and the overlap of the distributions when the material and structure are changed is also calculated by the same simulation calculations, thereby providing a current-injection OSLD with improved laser oscillation characteristics.

[0052] Preferred Embodiment of the Invention The present invention will be described below in detail with respect to the preferred embodiment shown in Figure 1a. However, the scope of the present invention should not be construed as being limited by the following specific description.

[0053] The properties of optically pumped organic semiconductor lasers (OSLs) have improved significantly over the past 20 years as a result of major advances in both the development of high-gain organic semiconductor materials and the design of high-Q-factor resonator structures. 1-5 The advantages of organic semiconductors as laser gain media include their high photoluminescence quantum yield (PLQY), large stimulated emission cross-section, and broad emission spectrum across the entire visible region, along with their chemically tunable and easy-to-process properties. Recent advances in low-threshold distributed feedback (DFB) OSLs have demonstrated optical pumping with electrically driven nanosecond pulsed inorganic light-emitting diodes, paving the way for new compact and low-cost visible laser technologies. 6 However, the ultimate goal is the electrically driven organic semiconductor laser diode (OSLD). The realization of OSLDs will enable the complete integration of organic photonics and optoelectronic circuits, as well as open up new applications in spectroscopy, display devices, medical devices (such as retinal displays, sensors, and photodynamic therapy devices), and LIFI telecommunications.

[0054] The main obstacles to achieving laser oscillation through direct electric pumping of organic semiconductors have been optical losses from electrical contacts and triplet and polaron losses that occur at high current densities. 4,5,7-9 To solve these fundamental loss problems, proposed methods include triplet absorption loss due to singlet-triplet exciton annihilation and triplet vanishing agents that suppress singlet vanishing. 10-12 The use of, and the spatial separation of the locations where exciton formation and exciton emission decay occur, minimizing the polaron vanishing process in the device active region. 13 One example is the reduction in size. However, organic light-emitting diodes (OLEDs) and optically pumped organic semiconductor DFB lasers have advanced. 5 Current-injected OSLD has not yet been fully demonstrated.

[0055] Previous studies have shown that achieving laser oscillation from an OSLD requires several kA / cm² if the additional losses associated with electropumping are completely suppressed. 2 This demonstrated that a current density exceeding [a certain value] is required. 14 One of the most promising molecules for realizing OSLD is 4,4'-bis[(N-carbazole)styryl]biphenyl (BSBCz) (chemical structure in Figure 1a). 15 The reason for this is the low spontaneous amplification emission (ASE) threshold of the thin film (0.30 μJ cm under 800 ps pulsed light excitation conditions). -2 ) 16 or, the maximum electroluminescence (EL) external quantum efficiency (η) exceeding 2% EQE Under 5μs pulse operation conditions, 2.8kA cm⁻¹ was observed in an OLED with the following characteristics: -2 The ability to withstand injection of extremely high current densities. 13 This is an excellent combination of optical and electrical properties. Furthermore, laser oscillation under long pulsed light excitation conditions of 30 ms at a high repetition rate of 80 MHz has recently been demonstrated with an optically pumped BSBCz-based DFB laser. 17The main reason this is possible is the extremely low triplet absorption loss of BSBCz thin films at the laser oscillation wavelength. Here, we demonstrate the first example of laser oscillation from electrically directly excited organic semiconductor thin films by developing and fully characterizing an OSLD based on BSBCz thin films in an inverted OLED structure with a mixed-order DFB SiO2 diffraction grating incorporated in the active region of the device.

[0056] Figures 1a and 2 schematically show the structure and fabrication of the OSLD developed in this study (see "Materials and Methods" for a detailed description of the experimental procedure). A mixed-order DFB diffraction grating with a region of 30 × 90 μm was created by imprinting an SiO2 sputtering layer onto an indium tin oxide (ITO) glass substrate using electron beam lithography and reactive ion etching (Figure 1b), and the device was completed by vacuum deposition of an organic layer and a metal cathode onto the substrate. The inventors designed a mixed-order DFB diffraction grating having primary and secondary Bragg scattering regions that provide strong optical feedback of laser radiation and efficient vertical power coupling, respectively. 17,18 Bragg condition 4,19 mλ Bragg =2n eff Λ m Based on this, diffraction grating periods (Λ1 and Λ2) of 140 and 280 nm were selected for the primary and secondary regions, respectively, where m is the diffraction order and λ is the diffraction order. Bragg This is the Bragg wavelength set to the maximum gain wavelength (477 nm) of the reported BSBCz, n eff This is the effective refractive index of the gain medium, calculated to be 1.70 in the case of BSBCz. 20,21 In the first set of characterized devices, the lengths of the primary and secondary DFB diffraction grating regions were 1.12 and 1.68 μm, respectively, and these are hereafter referred to as OSLDs.

[0057] Scanning electron microscope (SEM) images in Figures 1c and 1d show that the fabricated DFB diffraction grating had periods of 140±5 and 280±5 nm with a diffraction grating depth of approximately 65±5 nm. Complete removal of the SiO2 layer within the etching region to expose the ITO was crucial for good electrical contact with the organic layer, as confirmed by energy-dispersive X-ray spectroscopy (EDX) analysis (Figures 2c, 2d). Figures 1d and 1e show cross-sectional SEM and EDX images of the complete OSLD. The surface morphology of all layers exhibits a diffraction grating structure with a surface modulation depth of 50–60 nm. While the interaction of resonant laser modes with the electrodes is expected to reduce the Q coefficient of the feedback structure, such a diffraction grating structure on metal electrodes should also reduce the absorption loss of guided modes within the device structure. 22,23 .

[0058] The OSLD fabricated in this study has a simple inverted OLED structure of ITO (100 nm) / 20 wt% Cs:BSBCz (60 nm) / BSBCz (150 nm) / MoO3 (10 nm) / Ag (10 nm) / Al (90 nm) with energy levels as shown in Figure 3a. By doping the BSBCz thin film with Cs in the region close to the ITO junction, electron injection into the organic layer is improved, and MoO3 is used as a hole injection layer (Figure 4). The most efficient OLEDs generally use a multilayer structure to optimize charge equilibrium. 24,25 At high current densities, charge can accumulate at organic heterointerfaces, which can be detrimental to device performance and stability. 26 The OSLDs fabricated in this study contained only BSBCz as the organic semiconductor layer (optical amplification layer) and were specifically designed to minimize the number of organic heterointerfaces. To investigate the effect of the diffraction grating on the EL properties, a reference device without an SiO2DFB diffraction grating (hereinafter referred to as OLED) was also fabricated.

[0059] Figure 3b shows optical microscope images of the OSLD and reference OLED during 3.0V DC operation. In addition to the DFB diffraction grating described above, five other DFB diffraction grating shapes (Table 1) were optimized and characterized in the OSLD. EL is uniformly emitted from the active region of the reference OLED, but stronger emission can be observed from the secondary DFB diffraction grating region in the OSLD, which is specifically designed to promote vertical optical output coupling (Figures 3b and 5). Figures 2c and 2d show the current density-voltage (JV) and η of the OSLD and OLED under pulsed conditions (voltage pulse width 400 ns, repetition rate 1 kHz) at ambient temperature. EQE -J characteristics are shown, and the characteristics obtained under DC conditions are shown in Figure 6. SiO 2 While some current flows in the region above the diffraction grating (approximately 20% according to simulations), the majority flows in the region above the exposed ITO. For simplicity and consistency, the exposed ITO region is used to calculate the current density of all OSLDs, but this may be a slight overestimation.

[0060] [Table 1]

[0061] Values ​​for various diffraction grating shapes of the parameters shown in Figure 2, along with the total exposed ITO area A used to calculate the current density. The OSL is a 200 nm thick BSBCz layer deposited on a diffraction grating on quartz glass, and does not contain contacts.

[0062] Because pulsed operation reduces Joule heating, the maximum current density before device failure of the reference OLED is 6.6 A cm² under DC operating conditions. -2 From 5.7kA cm under pulse operation conditions -2 It increased to . Under DC operating conditions, all devices have a maximum η of more than 2% at low current densities. EQE This indicates 1A cm -2 At higher current densities, a strong efficiency roll-off is observed, which is presumed to be due to thermal degradation of the device. On the other hand, the efficiency roll-off of the OLED under pulsed operation conditions (Figure 3c,d) is consistent with previously reported values ​​of 110 A cm.-2 It started with a higher current density. 13 Furthermore, under pulsed operation conditions, efficient roll-off is suppressed within the OSLD, and furthermore, η EQE This is effectively 200A cm -2 It was found that the current density exceeded 2.2 kA cm² and reached a maximum value of 2.9%. -2 η at a higher level EQE The rapid decrease is likely due to thermal degradation of the device.

[0063] The EL spectrum of the OLED was similar to the steady-state PL spectrum of a neat BSBCz thin film (Figure 6c) and did not change as a function of current density. However, the EL spectrum from the glass surface of the OSLD under pulsed operation conditions narrowed its spectral lines as the current density increased (Figure 7a). -2 At lower values, a Bragg dip corresponding to the stopband of the DFB diffraction grating was observed at 478.0 nm (Figure 7b). When the current density exceeds this value, a strong spectral line narrowing, indicating the onset of laser oscillation, occurs at 480.3 nm. The intensity of the narrow emission peak was found to increase faster than that of the EL emission background, which is due to nonlinearity associated with stimulated emission.

[0064] Figure 7c plots the OSLD output intensity and full width at half maximum (FWHM) as a function of current. While the steady-state PL spectrum of a neat BSBCz thin film has an FWHM of approximately 35 nm, the FWHM of the OSLD at high current densities drops to less than 0.2 nm, a value close to the spectral resolution limit of the spectrometer used in this invention (0.17 nm for a wavelength range of 57 nm). The slope efficiency of the output intensity changes rapidly with increasing current, and this can be used to determine the current at 600 A cm -2 A threshold of (8.1mA) can be determined. 4.0kA cm -2 Beyond this point, the output intensity decreases with increasing current, presumably because the rapid rise in temperature damages the device, but the emission spectrum remains extremely sharp. This increase and subsequent decrease is due to η EQE- It matches the J curve. The maximum output measured with a power meter placed 3 cm away from the ITO glass substrate in front of the OSLD was 3.3 kA cm. -2 The power output was 0.50 mW (Figure 7d). These observed EL characteristics strongly indicate that optical amplification occurs at high current densities and that electrically driven laser oscillation is achieved above the current density threshold.

[0065] To provide further evidence that this is a laser oscillation, the beam polarization and shape were characterized. 9 The OSLD output beam is strongly linearly polarized along the diffraction grating pattern (Figure 8a), which is expected for laser emission from a one-dimensional DFB. The spatial profile of the focused OSLD emission (Figures 8b and 9a) shows the presence of a distinct Gaussian beam with a diameter of approximately 0.1 mm (Figure 8c), demonstrating the excellent focusing ability of the output beam from the OSLD above the laser oscillation threshold. When the beam is projected onto the screen, a fan-shaped pattern is formed as expected from the one-dimensional DFB (Figures 8d,e). The abrupt degradation above the threshold hindered interference spectroscopy at this stage, but the inventors found that the equation L=λ peak 2 The coherence length (L) is estimated from / FWHM, where λ peak The peak wavelength (1.1–1.3 mm for all devices in this report) matches the laser oscillation. Under photo-excitation conditions, where degradation is slower, the near-field beam patterns of similar device structures are similar both with and without electrodes (Figure 9b,c), further indicating that the device can support laser oscillation. Furthermore, the far-field pattern under photo-excitation conditions also matches the laser oscillation (Figure 9d).

[0066] The inventor cannot claim laser oscillation unless they have ruled out several phenomena that were previously misinterpreted as laser oscillation as the cause of the observed behavior. 9 The radiation from the inventor's OSLD is detected perpendicular to the substrate plane and exhibits clear threshold behavior, thus eliminating the line narrowing that occurs from end-face radiation of waveguide modes without laser amplification. 20,28,29While ASE appears similar to laser oscillation, the inventor's OSLD's FWHM (<0.2nm) is much narrower (several nanometers) than the typical ASE emission linewidth of organic thin films, and matches the typical FWHM of a photo-pumped organic DFB laser (<1nm). 5 The extremely narrow emission spectrum obtained by unintentionally inducing atomic transitions in ITO has been misinterpreted as emission from the organic layer. 30 However, the emission peak wavelength of the OSLD in Figure 7a is 480.3 nm, which cannot be due to emission from ITO, which has atomic spectral lines at 410.3, 451.3, and 468.5 nm. 31 .

[0067] If this is truly laser oscillation from a DFB structure, then the emission of the OSLD should be characteristic of the resonator mode, and its output should be susceptible to the modification of the laser resonator. Therefore, OSLDs with various DFB shapes, shown as OSLD-1 to OSLD-5 (Table 1), were manufactured and characterized (Figure 5), and it was confirmed that the emission wavelength could be tuned as expected, which is common to optically pumped organic DFB lasers. 4,5,32,33 The laser oscillation peaks are nearly identical for OSLD, OSLD-1, OSLD-2, and OSLD-3 (480.3 nm, 479.6 nm, 480.5 nm, and 478.5 nm, respectively), which have the same DFB diffraction grating period. Furthermore, OSLD-1, OSLD-2, and OSLD-3 all exhibit low minimum FWHM (0.20 nm, 0.20 nm, and 0.21 nm, respectively) and clear thresholds (1.2 kA cm, respectively). -2 , 0.8kA cm -2 and 1.1 kA cm -2 ) had. On the other hand, OSLD-4 and OSLD-5, which have different DFB diffraction grating periods, had an FWHM of 0.25 nm and a threshold of 1.2 kA cm -2 In this case, the wavelength is 459.0 nm (OSLD-4), the FWHM is 0.38 nm, and the threshold is 1.4 kA cm. -2 In this case, the laser oscillation peak was observed at 501.7 nm (OSLD-5). These results clearly demonstrate that the laser oscillation wavelength is controlled by the DFB shape.

[0068] To confirm that the laser oscillation threshold of the electrically driven OSLD matches that obtained by optical pumping, the laser oscillation characteristics of an OSLD (OLSD-6) optically pumped from the ITO side using an N2 laser (excitation wavelength 337 nm) emitting 3.0 ns pulses were measured (Figure 9e, f). The laser oscillation peak of OLSD-6 under optical pumping conditions (481 nm) matches that of the OSLD under electrically pumping conditions (480.3 nm). The laser oscillation threshold under optical pumping conditions is approximately 77 W cm² when considering only the output coupled to the device (simulation shows ~18%). -2 It was measured to be such that the threshold rise was smaller than that obtained with a photo-pumped BSBCz-based DFB laser without two electrodes (30W cm). -2 )teeth 17 This is the result of optimizing the layer thickness to minimize optical loss caused by the presence of electrodes. Assuming there is no additional loss mechanism of OSLD-6 at high current density, under electro-pumping conditions of 0.3 kA cm -2 The laser oscillation threshold can be predicted from the threshold under optical pumping conditions (see "Materials and Methods" for calculation details). Therefore, the 0.6~0.8 kA cm⁻¹ values ​​for OSLD and OSLD-2 (which has the same diffraction grating period as OSLD-6) are... -2 Observation of laser oscillation under electro-pumping conditions above the threshold is reasonable. Furthermore, the slope efficiency (Figures 9g-i) was similar under optical and electro-pumping conditions (0.4% and 0.3%, respectively), but was extremely high in the electrodeless optical pumping device (6%).

[0069] These results generally indicate additional losses that occur in OLEDs at high current densities (including exciton annihilation, triplet and polaron absorption, and loss due to high electric fields and Joule heating). 34However, this suggests that it was almost suppressed in BSBCz OSLDs. This is perfectly consistent with the fact that no EL efficiency roll-off was observed in OSLDs under strong pulsed electrical excitation conditions. The suppression of losses can be explained based on the characteristics of BSBCz and the device. As mentioned above, the BSBCz thin film did not exhibit large triplet losses (Figure 10a). 35 A reduction in the device's active region leads to a reduction in exciton loss caused by Joule heating. 36 The overlap between polaron absorption and emission spectra is minimal for both radical cations and radical anions within BSBCz, based on measurements of composite thin films of BSBCz:MoO3 and BSBCz:Cs, respectively (Figure 10b). Furthermore, while metal loss is a major problem in OLED structures, the DFB structure within the OSLD of the present invention reduces such losses by restricting light from the metal.

[0070] To further confirm that current-injection laser oscillation is occurring within the OSLD, electrical and optical simulations of the device were performed (Figure 11). Using carrier mobility extracted from fitting experimental data of a unipolar device (Figure 11a,b), the simulated J-V curves for devices with and without diffraction gratings agree well with the experimental characteristics (Figure 11a,c,d), indicating that etching is sufficient to make electrical contact with ITO in the device with a diffraction grating. The recombination rate profile (Figure 11e,f) shows the periodic changes within the device due to periodic injection of electrons from the ITO electrode through the insulating SiO2 diffraction grating. Similar to recombination, the exciton density (S) is spread across the entire thickness of the organic layer (Figure 12a), but is mainly concentrated in regions where SiO2 does not obstruct the cathode-to-anode path. The average exciton densities of the OSLD and OLED are similar (Figure 11g), indicating that high exciton accumulation near SiO2 compensates for the lower exciton density between the diffraction grating (where there is no injection region), resulting in an exciton density similar to that of the reference device.

[0071] Optical output coupling from the secondary diffraction grating and optical confinement within the ITO layer constitute waveguide losses and are clearly visible in the simulated electric field distribution E(x,y) of the optical field at the calculated resonance wavelength λ0 = 483 nm within the OSLD (Fig. 12b). The DFB resonant cavity is characterized by a confinement factor Γ of 40% and a Q factor of 255, which is consistent with the Q factor of 204 calculated from Fig. 7b using λ peak / FWHM. The modal gain (g m ) is an indicator of the amplification of light in the laser mode and, as a function of the current density, the spontaneous emission cross-section σ 35 of BSBCz stim is calculated from the overlap of the exciton density distribution and the optical field distribution for a case of 2.8x10 -16 cm 2 (see "Materials and Methods" for details) and is shown in Fig. 12c for the second order region. A higher modal gain above 500 A cm -2 is consistent with the observation of laser oscillation. The insulating DFB structure aids in enhancing the coupling to the optical mode by localization of high exciton density in and above the valleys of the diffraction grating (Fig. 12a), where the optical mode is strong (Fig. 12b), resulting in high values at J = 500 A cm -2 in Fig. 12d.

[0072] In conclusion, the present invention demonstrates that laser oscillation from a current-driven organic semiconductor can suppress losses and enhance coupling through appropriate design and selection of the resonator and the organic semiconductor. The laser oscillation demonstrated here has been reproduced in multiple devices and fully characterized to exclude other phenomena that could be misinterpreted as laser oscillation. The results fully support the claim of being the first observation of electrical pumping laser oscillation in an organic semiconductor. The low losses of BSBCz are essential to enable laser oscillation, and thus the important next step is the development of strategies for designing new laser molecules with similar or improved properties. This report opens up new possibilities in organic photonics and forms the basis for the future development of organic semiconductor laser diode technology that can enable a simple, inexpensive, tunable, fully and directly integrated organic optoelectronic platform.

[0073] Materials and Methods (Device manufacturing) An indium tin oxide (ITO) coated glass substrate (100 nm thick ITO, Atsugi Micro Co., Ltd.) was cleaned by ultrasonic treatment using neutral detergent, pure water, acetone, and isopropanol, and then treated with ultraviolet ozone. A 100 nm thick SiO2 layer (which will become a DFB diffraction grating) was sputtered onto the ITO coated glass substrate at 100°C. The argon pressure during sputtering was 0.66 Pa. The high-frequency power was set to 100 W. The substrate was cleaned again by ultrasonic treatment using isopropanol, and then treated with ultraviolet ozone. The SiO2 surface was treated with hexamethyldisilazane (HMDS) by spin coating at 4,000 rpm for 15 seconds, and then annealed at 120°C for 120 seconds. A resist layer with a thickness of approximately 70 nm was spin-coated onto a substrate using a ZEP520A-7 solution (ZEON Co.) at 4,000 rpm for 30 seconds, and then fired at 180°C for 240 seconds.

[0074] Using the JBX-5500SC system (JEOL), 0.1 nC cm -2Electron beam lithography with an optimized dose was performed to draw a diffraction grating pattern on the resist layer. After electron beam irradiation, this pattern was developed in a developer (ZED-N50, ZEON Co.) at room temperature. Using the pattern resist layer as an etching mask, the substrate was plasma-etched with CHF3 using an EIS-200ERT etching system (ELIONIX). The substrate was plasma-etched with O2 using a FA-1EA etching system (SAMCO) to completely remove the resist layer from the substrate. The etching conditions were optimized to completely remove SiO2 from the DFB grooves until the ITO was exposed. The diffraction grating formed on the SiO2 surface was observed by SEM (SU8000, Hitachi) (Figure 1c). EDX (6.0 kV, SU8000, Hitachi) analysis was performed to confirm that SiO2 was completely removed from the DFB grooves (Figures 2c, d). Cross-sectional SEM and EDX were measured by Kobelco using a cold field emission SEM (SU8200, Hitachi High-Technologies), energy-dispersive X-ray spectroscopy (XFlash FladQuad 5060, Bruker), and a focused ion beam system (FB-2100, Hitachi High-Technologies) (Figures 1d, e).

[0075] The DFB substrate was cleaned by conventional ultrasonic treatment. Next, an organic layer and a metal electrode were vacuum-evaporated by thermal evaporation at a total evaporation rate of 1.5 x 10 -4 Pa under a pressure of 0.1 - 0.2 nm s -1 to fabricate an OSLD having a structure of indium tin oxide (ITO) (100 nm) / 20 wt% BSBCz:Cs (60 nm) / BSBCz (1 f50 nm) / MoO3 (10 nm) / Ag (10 nm) / Al (90 nm). The SiO2 layer on the ITO surface served as an insulator in addition to the DFB diffraction grating. Therefore, the current region of the OLED was limited to the DFB region where BSBCz was in direct contact with the ITO. Also, a reference OLED having an active region of 30 x 45 μm in the same current flow region was fabricated.

[0076] (Device Characterization) To prevent degradation from moisture and oxygen, all devices were encapsulated in a nitrogen-filled glove box using a glass lid and UV-curing epoxy resin. Current density-voltage-η for OSLD and OLED. EQE (JV-η EQE The characteristics (DC) were measured at room temperature using an integrating sphere system (A10094, Hamamatsu Photonics). For pulse measurements, a pulse generator (NF, WF1945) was used to apply rectangular pulses with a pulse width of 400 ns, pulse period of 1 μs, repetition frequency of 1 kHz, and various peak currents to the device at ambient temperature. Using these conditions, the inventors were able to draw approximately 1 kA cm from a good batch to a properly functioning OSLD before electrical damage occurred. -2 (Near the threshold) 50 pulses, 2kA cm -2 20 pulses and 3 kA cm -2 Ten pulses were successfully applied. This process yielded approximately 500 devices with a yield of about 5%. The JV-luminance characteristics under pulsed driving conditions were measured using an amplifier (NF, HSA4101) and a photomultiplier tube (PMT) (C9525-02, Hamamatsu Photonics). Both the PMT response and the driving square wave signal were measured using a multi-channel oscilloscope (Agilent Technologies, MSO6104A). The number of photons calculated from the PMT response EL intensity, along with the correction factor, was divided by the number of injected electrons calculated from the current to obtain η. EQE The calculation was performed. The output power was measured using a laser power meter (OPHIR Optronics Solution Ltd., StarLite 7Z01565).

[0077] To measure the spectrum, both optically pumped and electrically pumped OSLD emitted laser light was collected perpendicular to the device surface using an optical fiber connected to a multi-channel spectrometer (PMA-50, Hamamatsu Photonics) and placed 3 cm away from the device. The beam profile of the OSLD was confirmed using a CCD camera (beam profiler WimCamD-LCM, DataRay). To determine the characteristics of OSLD-6 and OSL under optical pumping conditions, pulsed excitation light from a nitrogen gas laser (NL100, N2 laser, Stanford Research System) was passed through a lens and slit to the device at a rate of 6 × 10⁻⁶. -3 cm 2 The beam was focused into a specific region. The excitation wavelength was 337 nm, the pulse width was 3 ns, and the repetition rate was 20 Hz. The excitation light was incident on the device at approximately 20° to the normal to the device plane. The excitation intensity was controlled using a set of neutral filters. Steady-state PL spectroscopy was monitored using the spectrofluorometer (FP-6500, JASCO) shown in Figure 10 and the spectrometer (PMA-50) shown in Figure 6. Near-field images of the OSL and OSLD-6 were captured using a laser beam profiler (C9334-01, Hamamatsu Photonics) equipped with a near-field optical element (A4859-06, Hamamatsu Photonics), and far-field images of the OSL were captured using the same profiler and near-field optical element (A3267-11, Hamamatsu Photonics).

[0078] The lower limit of the electric laser oscillation threshold was determined from the optical threshold using the following formula.

[0079]

number

[0080] Here, P th λ, h, c, η out , φ PL η EQEP and e are the optical pumping threshold, wavelength, Planck constant, speed of light, device output coupling ratio, photoluminescence quantum yield of BSBCz, external quantum efficiency of BSBCz OSLD, and elementary charge, respectively. This equation simply states that the proportion of singlets produced under electrically excited conditions is P th We seek to determine the current density that must be equal to that under photoexcitation conditions. This formula does not consider the additional loss mechanism that occurs under electrical excitation conditions at high current densities. The inventors η out 20% and φ PL 76% was used (from Table 2). η EQE By repeatedly adjusting several values ​​in Figure 3d to closely match J, the inventor finally arrived at η EQE The coefficient was determined to be 2.1%. The coefficient of 2 takes into account that when calculating the current density of the OSLD in this paper, the inventor used only half of the exposed ITO region of the entire diffraction grating region.

[0081] (Device modeling and parameters) Optical simulations of a resonant DFB cavity were performed using Comsol Multiphysics 5.2a software. The Helmholtz equations for all frequencies were solved using the finite element method (FEM) in the Comsol software's radio frequency module. Each layer was represented by its complex refractive index and thickness. The computational domain was limited to a single supercell consisting of a second-order diffraction grating surrounded by a first-order diffraction grating. Floquet periodic boundary conditions were applied to the transverse boundary, and scattering boundary conditions were used for the upper and lower domains. Only the TE mode was considered, as the TM mode suffers less loss than the TE mode (due to metallic absorption).

[0082] Charge transport within the OSLD was described using a two-dimensional time-independent drift-diffusion equation coupled with a Poisson equation, and a continuity equation for charge carriers using Technology Computer Aided Design (TCAD) software from Silvaco. Electron and hole concentrations were represented using parabolic density of states (DOS) and Maxwell-Boltzmann statistics. The trap distribution within the organic semiconductor was modeled using a Gaussian distribution. 37The charge carrier mobility was assumed to be field-dependent and have a pool-Frenkel configuration. 38,39 In this model, energy disorder is not considered, and therefore, the validity of Einstein's relation was assumed to calculate the charge carrier diffusion constant from the charge carrier mobility. The recombination rate R is given by the Langevin model. 40 The continuity equation for singlet excitons was solved considering exciton diffusion, emission, and non-radiative processes.

[0083] The charge carrier mobility was extracted by fitting experimental data (energy diagrams and structures in Figure 4) of hole-only and electron-only devices. Table 2 shows the values ​​of the fitted mobility parameters and other input parameters used in the simulation. Using the extracted values, a bipolar OLED device with the structure ITO / 20 wt%Cs:BSBCz(10 nm) / BSBCz(190 nm) / MoO3(10 nm) / Al was simulated. The work function of the cathode (ITO / 20 wt%Cs:BSBCz) was 2.6 eV, and the work function of the anode (MoO3 / Al) was 5.7 eV. The effect of the DFB diffraction grating on the electrical properties of the OSLD was calculated and compared with a reference device (without a diffraction grating). The following equations were used to express S(x,y) and optical mode intensity |E(x,y)|. 2 From mode gain g m I calculated it.

[0084]

number

[0085] Here, L is the cavity length (secondary diffraction grating region only), and d is the active film thickness.

[0086] Near-field and far-field images were simulated using the OptiFDTD software package (Optiwave). Near-field images were simulated using the FDTD method. From these images, far-field images were calculated using the Fraunhofer approximation. A perfectly matching layer and periodic conditions were used as boundary conditions.

[0087] [Table 2]

[0088] ε r E is the relative permittivity of the material. HOMO and E LUMO These are the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), respectively. HΟΜΟ and N LUMO This represents the density of states of the HOMO and LUMO levels. tp This is the total trap density, and E tp σ is the energy depth of the trap above the HOMO level, tp μ is the width of the Gaussian distribution. n0 and μ p0 F is the zero field mobility. n0 and F p0 These are the characteristic electric fields of electrons and holes, respectively. r k is the radiative decay constant. nr φ is the non-radiative decay constant. PL L is the photoluminescence quantum yield. s is the exciton diffusion distance. As an approximation, the mobility of BSBCz:Cs was set to be the same as that of BSBCz, and as a result, the fit with the experimental data was good, and therefore the mobility was not further improved.

Claims

1. A method for designing a current-injection organic semiconductor laser diode having an optical amplification layer containing an organic semiconductor, A method for designing a current-injected organic semiconductor laser diode, comprising the step of designing the material and structure of the current-injected organic semiconductor laser diode such that the mode gain (gm), as a function of current density obtained by the following formula from the overlap of the exciton density distribution in the xy plane of the optical amplification layer during current injection (where y is the thickness direction of the organic light-emitting layer and x is orthogonal to y) and the electric field intensity distribution of the resonant optical mode, is greater than or equal to the oscillation threshold gain at a current density of 500 A·cm⁻². [Math 1] [In the equation, σstim represents the area of ​​the stimulated radiation cross-section, E(x,y) represents the electric field intensity distribution of the resonant optical mode in the xy plane, S(x,y) represents the exciton density distribution in the xy plane, L represents the resonator length of the optical resonator structure, and d represents the thickness of the optical amplification layer. The electric field intensity distribution of the resonant optical mode can be obtained by solving Helmholtz's equation, and the exciton density distribution can be obtained by solving the continuity equation for singlet excitons.]

2. The method according to claim 1, wherein the current-injection organic semiconductor laser diode includes an optical resonator structure, one or more organic layers including an optical amplification layer containing an organic semiconductor, and a pair of electrodes formed separately from the organic layers, and the one or more organic layers are formed on the surface of a substrate which is composed of one of the pair of electrodes and an optical resonator structure composed of an insulator.

3. A method for designing a current-injection organic semiconductor laser diode having an optical amplification layer containing an organic semiconductor, The calculation means includes the step of calculating the mode gain (gm) using the following formula from the overlap between the exciton density distribution and the electric field intensity distribution of the resonant optical mode in the xy plane (y is the thickness direction of the organic light-emitting layer and x is perpendicular to y) of the optical amplification layer during current injection in a designed or existing diode, A method comprising the steps of designing a new diode by changing at least one of the material and structure of a pre-designed or existing diode such that the mode gain (gm), which is obtained by the following formula from the overlap of the exciton density distribution in the xy plane of the optical amplification layer during current injection (where y is the thickness direction of the organic light-emitting layer and x is the direction orthogonal to y) and the electric field intensity distribution of the resonant optical mode, is higher than the calculated value of the mode gain (gm) obtained by the calculation means. [Math 2] [In the equation, σstim represents the area of ​​the stimulated radiation cross-section, E(x,y) represents the electric field intensity distribution of the resonant optical mode in the xy plane, S(x,y) represents the exciton density distribution in the xy plane, L represents the resonator length of the optical resonator structure, and d represents the thickness of the optical amplification layer. The electric field intensity distribution of the resonant optical mode can be obtained by solving Helmholtz's equation, and the exciton density distribution can be obtained by solving the continuity equation for singlet excitons.]

4. The method according to claim 3, wherein the current-injection organic semiconductor laser diode includes an optical resonator structure, one or more organic layers including an optical amplification layer containing an organic semiconductor, and a pair of electrodes formed separately from the organic layers, and the one or more organic layers are formed on the surface of a substrate which is composed of one of the pair of electrodes and an optical resonator structure composed of an insulator.

5. A program for designing a current-injection organic semiconductor laser diode having an optical amplification layer containing an organic semiconductor, the program for causing a computer to function as the design means in order to carry out the method according to claim 1.

6. A program for designing a current-injection organic semiconductor laser diode having an optical amplification layer containing an organic semiconductor, the program for causing a computer to function as the calculation means and the design means in order to carry out the method according to claim 3.

7. The program according to claim 5 or 6, wherein the current-injection organic semiconductor laser diode includes an optical resonator structure, one or more organic layers including an optical amplification layer containing an organic semiconductor, and a pair of electrodes formed separately from the organic layers, and the one or more organic layers are formed on the surface of a substrate composed of one of the pair of electrodes and an optical resonator structure made of an insulator.

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