A method and apparatus for in-situ differential absorption spectroscopy of an electroluminescent device

Abstract

The application discloses a kind of synchronous measurement method and device of electroluminescent device in-situ differential absorption spectrum.The method is used to carry out frame-level synchronization between pulsed broadband xenon lamp and CCD frame acquisition by external electronic trigger signal without interrupting the continuous electric bias of device: probe light is only triggered to light in odd numbered exposure frame, and even frame remains off.By subtracting the intensity of adjacent odd and even frames, the electroluminescence and dark noise generated during device operation are eliminated, the net probe light transmission signal is extracted, and the differential absorption spectrum ΔA is calculated;At the same time, the EL spectrum at the same time is directly obtained from the even frame.The device uses a reflective optical path, is compatible with the complete device structure with an opaque metal back electrode, and is equipped with a reference detector to normalize and correct the pulse intensity fluctuations in real time.The application can be used for in-situ synchronous characterization of multiple degradation / enhancement channels during the aging process of thin-film electroluminescent devices.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic device characterization technology, and specifically to a method and apparatus for synchronously measuring in-situ differential absorption spectrum and electroluminescence spectrum by frame synchronization pulse detection under continuous electrical bias operation of a thin-film electroluminescent device. Background Technology

[0002] The operational stability of thin-film electroluminescent devices (such as QLEDs and OLEDs) is a key bottleneck restricting their commercialization. Existing characterization methods have the following limitations:

[0003] (1) Optical pump differential absorption spectrum: The excitation source is a light pulse, which cannot directly reflect the actual carrier occupancy state of the device under electric drive conditions. Furthermore, strong light excitation may introduce additional photo-induced defects, interfering with the intrinsic aging behavior of the device.

[0004] (2) Electrically modulated absorption spectrum: Differential signals are generated by modulating the voltage applied to the device. This requires periodic interruption or disturbance of the electrical bias, which disrupts the continuous working state of the device and makes it impossible to achieve true in-situ online monitoring.

[0005] (3) Conventional transmission differential absorption spectroscopy: It is suitable for solution or thin film samples, but not for complete device structures with opaque metal back electrodes; and when the device is in operation, the electroluminescence signal emitted by the device itself will be superimposed on the probe light signal, causing serious interference, and there is currently no mature elimination solution.

[0006] Therefore, existing technologies cannot perform in-situ differential absorption spectroscopy measurements on complete electroluminescent devices with opaque metal electrodes without interrupting electrical bias, and cannot achieve synchronous acquisition with EL spectroscopy. Summary of the Invention

[0007] This invention provides a method and apparatus for synchronous measurement of in-situ differential absorption spectra of electroluminescent devices, aiming to solve the core technical problems encountered in existing technologies when performing differential absorption spectral characterization of electroluminescent devices in continuous operation, such as the inability to eliminate self-emission interference, the necessity of interrupting or modulating electrical bias, and the inability to synchronously acquire differential absorption and electroluminescence spectra. To achieve the above objectives, this invention adopts the following technical solution:

[0008] A method for synchronous measurement of in-situ differential absorption spectra of electroluminescent devices includes the following steps:

[0009] During the preparation phase, under the condition of applying zero bias voltage to the device under test, two sets of background spectra were acquired: the dark background frame I when the probe light was off. bg,off And the unbiased transmission background frame I when the probe light is turned on. bg,on ;

[0010] The measurement phase includes executing alternating frame triggering and spectral extraction processes once or multiple times;

[0011] Alternating frame triggering process steps: Apply a continuous constant electrical bias to the device under test without interruption; simultaneously control the pulse probe light source with an external electronic trigger signal so that the probe light is triggered and lit only in odd-numbered CCD exposure frames, and remains off in even-numbered frames, forming an alternating "on / off" frame sequence of the probe light; and the pulse width falls completely within the corresponding integration window;

[0012] The spectral extraction process steps are as follows: after subtracting the dark background from the even-numbered frames, the electroluminescence spectrum (EL) of the device under test at the current moment is extracted; the net probe intensity is extracted from the difference between adjacent odd-numbered frames and even-numbered frames, and the differential absorption spectrum is calculated; thus, the synchronous in-situ acquisition of ΔA and EL spectra is achieved while the device is in continuous operation.

[0013] The differential absorption spectrum is calculated using the following formula: ΔA = - log[(I on - I off ) / (I bg,on - I bg,off )], where I on For odd-numbered detection frame strength, I off The intensity is the intensity of adjacent even-numbered frames; the subtraction operation is used to eliminate the common electroluminescence and dark noise contributions of adjacent frames.

[0014] A synchronous measurement device for in-situ differential absorption spectra of electroluminescent devices, comprising:

[0015] The pulse detection light source acquires trigger pulse signals through an external electronic trigger interface and outputs detection light.

[0016] A shaping lens group is used to shape the probe light output from the pulse probe light source into near-parallel light output;

[0017] The beam splitter, using a beam splitting cube, is placed on the probe light path to split the near-parallel probe light according to preset ratio parameters. One beam is output as a reference light to the spectrometer to correct inter-pulse intensity fluctuations, and the other beam is output as the main probe light to the focusing lens group.

[0018] The first focusing lens group is used to focus the main probe beam so that the input near-parallel beam illuminates the device under test at a set incident angle.

[0019] The device under test is a thin-film electroluminescent device with self-emissive properties. It is placed at a preset distance in front of the focal point of the focusing lens group to ensure that the diameter of the light spot reaching the device surface is larger than the diameter of the light spot at the focal point, thereby reducing the power density of the probe light and avoiding photodegradation that causes optical damage to the device. The probe light passes through the transparent electrode, hole transport layer, light-emitting layer and electron transport layer of the device under test in sequence, and is reflected by the metal reflective electrode, returning along the original path and outputting from the surface.

[0020] The second focusing lens group is used to focus and collect the main probe light reflected by the device under test;

[0021] The spectrometer, including a monochromator and a CCD camera, receives reference light and reflected detection light, performs dispersion and detection, and uploads the detected spectral data to the host computer.

[0022] A continuous bias power supply is used to apply a continuous constant current or constant voltage bias to the device under test throughout the measurement process.

[0023] The host computer includes a front-end interface and a control backend. The front-end interface is used to collect user-input parameters and control commands, and to visualize the measurement results. The control backend includes a memory and a processor. The memory stores program modules, and the processor loads the program to execute the steps of the method described in claims 1-2 to control the pulse detection light source, spectrometer, and continuous bias power supply during the preparation stage and the timing control during the measurement stage, thereby completing the in-situ differential absorption spectroscopy measurement of the electroluminescent device.

[0024] The pulse detection light source is a broadband pulse xenon lamp.

[0025] The host computer control backend stores the following program modules:

[0026] The trigger synchronization control module is used to generate a periodic trigger signal synchronized with the CCD frame sequence, and control the pulse detection light source to only light up within the odd-numbered frame integration window; it also outputs a timestamp signal synchronized with the CCD frame sequence to the spectrometer, which is used to align the spectral data with the real-time current-voltage characteristics of the device under test and record them on the time axis.

[0027] The continuous bias power supply module is used to output control commands to the continuous bias power supply only during the measurement phase, so as to control it to apply a continuous constant current or constant voltage bias to the device under test without interrupting the device's operating state.

[0028] The data processing module will combine the acquired even-numbered frame spectral data with the dark background frame I. bg,off The difference is calculated as the electroluminescence spectrum EL of the device under test at the current moment; the net probe intensity is extracted from the difference between adjacent odd-numbered and even-numbered frames of spectrum, and the differential absorption spectrum ΔA is calculated using the following formula: ΔA = -log[(I on- I off ) / (I bg,on - I bg,off )], where I on For odd-numbered detection frame strength, I off The intensity of adjacent even-numbered frames.

[0029] The electroluminescent devices include quantum dot light-emitting diodes (QLEDs), organic light-emitting diodes (OLEDs), and perovskite light-emitting diodes (PeLEDs).

[0030] The user-input parameters and control commands include: wavelength and on / off commands for the pulse detection light source; frame rate and on / off commands for the spectrometer; and constant current or constant voltage values ​​and on / off commands for the continuous bias power supply.

[0031] Compared with the prior art, the present invention has the following significant technical effects:

[0032] First, EL self-emission interference is completely eliminated at the signal principle level, making it suitable for devices of any EL intensity level. Second, the device maintains continuous operating bias throughout the entire process, and the obtained ΔA spectrum truly reflects the changes in the absorption state of the device under stable electric drive conditions, avoiding artificial disturbances introduced by bias modulation. Third, the differential absorption spectrum and EL spectrum are output synchronously in each acquisition cycle, supporting time axis alignment analysis and decoupling of multiple aging mechanisms. Fourth, the reflective optical path design gives the device universal compatibility with fully packaged or unpackaged thin-film electroluminescent devices, without the need to modify the optical path structure for different device types. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the test method.

[0034] Figure 2 The EL spectrum of the QLED in Example 1 changes with aging time.

[0035] Figure 3 The electro-excitation differential absorption spectrum of the QLED in Example 1 changes with aging time.

[0036] Figure 4 To Figure 3 After performing multi-band dynamic analysis on the differential absorption spectrum, the decoupled components of each independent aging channel and the driving voltage are shown in the figure as a function of aging time. Detailed Implementation

[0037] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0039] This invention proposes a frame-level synchronous triggering scheme that precisely binds the lighting sequence of the pulse broadband probe light source with the frame acquisition sequence of the CCD camera at the hardware level. Specifically, the continuously acquired CCD frames are divided into two categories according to odd and even numbers: the external electronic trigger signal controls the pulse probe light source (xenon lamp) to discharge only within the integration window of odd-numbered frames, with each pulse width falling completely within the corresponding integration window, ensuring that the probe light intensity is completely captured without inter-frame crosstalk; the probe light remains off in even-numbered frames. Throughout the entire measurement process, the device maintains a continuous constant current or constant voltage bias, and its operation is unaffected by any interruption or disturbance.

[0040] Within the aforementioned acquisition framework, the signal recorded in odd-numbered frames is the sum of the probe light transmission intensity, device electroluminescence (EL), and dark noise (Ion), while the signal recorded in even-numbered frames is the sum of the device EL and dark noise (Ioff). Since the time interval between adjacent odd and even frames is extremely short (on the order of milliseconds, much smaller than the rate of change of device EL intensity over the aging timescale), it is reasonable to assume that the device EL intensity within adjacent frames is approximately equal. Therefore, subtracting Ion from Ioff from the two frames can, in principle, completely eliminate EL contribution and dark noise without any optical filters, accurately separating the net probe light transmission signal. Combined with the background frames pre-acquired under zero bias conditions, the differential absorption spectrum ΔA is calculated. Simultaneously, the even-numbered frames (probe light off frames), after subtracting the dark background, directly provide the device's EL spectrum at that moment, without any additional measurement steps. This means that within each acquisition cycle, the ΔA spectrum and the EL spectrum are acquired synchronously on the same time axis, achieving strict time alignment of the two physical quantities.

[0041] The measuring device is constructed according to the scheme described in this invention, such as... Figure 1This is a schematic diagram of the measurement method and apparatus of the present invention. The apparatus includes: a pulsed white light source, a shaping lens group, a beam splitter, a first achromatic cemented doublet lens group, a second achromatic cemented doublet lens group, a device under test, a source meter, a spectrometer, and a host computer. The host computer includes a front-end interface and a control back-end. The front-end interface is used to collect user-input parameters and control commands, and to visualize the measurement results. The control back-end includes a memory and a processor. The memory stores program modules: a synchronous triggering module, a continuous bias power supply module, and a data processing module. The program executes to control the pulsed detection light source, the spectrometer, and the continuous bias power supply during the preparation stage and the timing control during the measurement stage, thereby completing the in-situ differential absorption spectroscopy measurement of the electroluminescent device.

[0042] The diagram illustrates the optical path connections and the parity trigger timing of the trigger synchronization control module and the CCD frame sequence. The optical path employs a reflective configuration. The device under test (DUT) is fixed at the measurement position with the ITO surface facing the probe light direction, eliminating the need for a dedicated sample stage. A pulsed broadband xenon lamp serves as the probe light source, and its external electronic trigger interface receives TTL trigger pulses output from the synchronization control module. The trigger signal is generated by a digital delay generator and is strictly synchronized with the frame acquisition timing of the CCD camera: odd-numbered frames in the CCD frame sequence correspond to trigger pulse output (probe light on), while even-numbered frames correspond to trigger pulse suppression (probe light off). The width of each xenon lamp discharge pulse is set to completely fall within the corresponding CCD integration window, ensuring complete capture of probe light energy and preventing probe light crosstalk between adjacent frames.

[0043] After the probe light is emitted, it is shaped into parallel light output by a shaping lens group. Then, it is split into two paths by a 90:10 unpolarized broadband beam splitter: 10% of the light intensity is guided to a reference CCD to record the absolute intensity of each pulse in real time for subsequent frame-by-frame normalization correction; the 90% main light path is shaped into a near-parallel beam by a first achromatic cemented doublet lens group and then illuminates the QLED device under test at a certain incident angle. The device is fixed on a translation stage with the ITO surface facing the incident light direction, and the device plane is placed about 1 cm in front of the focal point of the lens group to ensure that the diameter of the light spot reaching the device surface is larger than the diameter of the light spot at the focal point, thereby reducing the probe light power density and avoiding interference from photo-induced degradation on the intrinsic aging behavior of the device.

[0044] The probe light passes sequentially through the ITO transparent anode, the PEDOT:PSS hole injection layer, the TFB hole transport layer, the QD emitting layer, and the ZnMgO electron transport layer. It undergoes specular reflection at the Ag metal cathode and then returns along an approximately original path. After being collected by another achromatic cemented doublet lens group, the light is used by a CCD camera to perform spectral detection.

[0045] Before applying any operating bias to the device, two sets of background spectra were first acquired. The first set is the dark background frame I. bg,offThe probe light is turned off, the device is at zero bias, and the CCD acquires several frames at the standard integration time, averages them, and records the system's dark noise substrate. The second group is static transmission background frame I. bg,on The probe light trigger is activated, the device is kept at zero bias, and several frames of probe light activation are collected and averaged to record the background transmission spectrum of the device to the probe light without bias, which is used as the reference baseline for differential absorption. All the above background data acquisition is completed before the start of the formal aging experiment, and the optical path is kept in a fixed collimated state throughout the process.

[0046] After background acquisition is completed, a continuous constant current bias (or constant voltage bias) is applied to the device to drive the QLED into continuous operation, and the aging timer begins from this moment. The CCD camera then continuously acquires data at a preset frame rate, triggering the synchronization control module to synchronously output an alternating odd and even trigger signal, forming a stable "probe light on / off" alternating frame sequence. The reference detector synchronously records the pulse intensity value corresponding to each probe light on frame for normalization purposes.

[0047] The data processing module processes the real-time acquired frame sequence frame by frame according to the following procedure: First, it classifies frames according to their odd or even numbers, pairing consecutive odd and even frames; for each frame pair, it processes the odd-numbered frames I after reference strength normalization. on With adjacent even-numbered frames I off The net probe light transmission intensity I was obtained. on - I off This difference, in principle, completely eliminates the contribution of EL signal and dark noise during device operation; subsequently, combined with the pre-acquired background frame, the differential absorption spectrum at that moment is calculated using the following formula: ΔA = -log[(I on - I off ) / (I bg,on - I bg,off Meanwhile, after subtracting the dark background from the even-numbered frames (probe light off frames), the device EL spectrum at that moment is directly output: EL(λ,t) = I off (λ,t) - I bg,off (λ). The two spectra mentioned above share the same timestamp in each acquisition cycle, achieving strictly synchronized output. By repeating the above process at preset time intervals, the time series datasets of ΔA(λ,t) and EL(λ,t) throughout the entire aging experiment cycle can be obtained.

[0048] Example 1:

[0049] The bottom-emission QLED structure of the thin-film electroluminescent device used in the experiment of this invention is ITO / PEDOT:PSS / TFB / QD / ZnMgO / Ag. Figure 2This is the evolution of the EL spectrum extracted synchronously from even-numbered frames (probe light off frames) of the QLED in Example 1 under continuous constant current 2mA bias driving as a function of aging time. The results show that the EL peak intensity monotonically increases with aging time, and the peak position does not shift significantly, indicating that the radiative recombination efficiency of the device continuously improves during the forward aging process. Figure 3 The following is an example of the evolution of the electro-excited differential absorption spectrum (ΔA) of the QLED obtained synchronously by the method of the present invention under the same aging conditions in Example 1. A monotonically increasing ground-state bleaching signal can be observed in the first exciton absorption peak band of the QD (approximately 528 nm), indicating that the trapped states in the QD layer are gradually filled and the occupancy of ground-state carriers increases. An independently evolving differential absorption signal can be observed in the characteristic absorption band of ZnMgO, which is distinguishable from the QD bleaching signal in terms of kinetic characteristics, corresponding to the gradual filling process of electron traps in the ZnMgO layer. Figure 4 The diagram shows the changes in the composition of multiple independent aging channels obtained by decoupling the QLED electro-excited differential absorption spectrum in Example 1 after multi-band kinetic analysis, as a function of aging time. The first channel corresponds to the luminescence enhancement caused by the filling of QD layer traps, and the second channel corresponds to the decrease in driving voltage caused by the filling of ZnMgO layer traps. The difference in their kinetic curves on the time axis verifies that the two aging channels are independent of each other, and quantitative decoupling can be achieved by the method of this invention.

[0050] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for synchronous measurement of in-situ differential absorption spectra of electroluminescent devices, characterized in that, Includes the following steps: During the preparation phase, under the condition of applying zero bias voltage to the device under test, two sets of background spectra were acquired: the dark background frame I when the probe light was off. bg,off And the unbiased transmission background frame I when the probe light is turned on. bg,on ; The measurement phase includes executing alternating frame triggering and spectral extraction processes once or multiple times; Alternating frame triggering process steps: Apply a continuous constant electrical bias to the device under test without interruption; simultaneously control the pulse probe light source with an external electronic trigger signal so that the probe light is triggered and lit only in odd-numbered CCD exposure frames, and remains off in even-numbered frames, forming an alternating "on / off" frame sequence of the probe light; and the pulse width falls completely within the corresponding integration window; The spectral extraction process steps are as follows: after subtracting the dark background from the even-numbered frames, the electroluminescence spectrum (EL) of the device under test at the current moment is extracted; the net probe intensity is extracted from the difference between adjacent odd-numbered frames and even-numbered frames, and the differential absorption spectrum is calculated; thus, the synchronous in-situ acquisition of ΔA and EL spectra is achieved while the device is in continuous operation.

2. The synchronous measurement method for in-situ differential absorption spectrum of an electroluminescent device according to claim 1, characterized in that, The differential absorption spectrum is calculated using the following formula: ΔA = - log[(I on - I off ) / (I bg,on - I bg,off )], where I on For odd-numbered detection frame strength, I off The intensity is the intensity of adjacent even-numbered frames; the subtraction operation is used to eliminate the common electroluminescence and dark noise contributions of adjacent frames.

3. A synchronous measurement device for in-situ differential absorption spectra of an electroluminescent device, characterized in that, include: The pulse detection light source acquires trigger pulse signals through an external electronic trigger interface and outputs detection light. A shaping lens group is used to shape the probe light output from the pulse probe light source into near-parallel light output; The beam splitter, using a beam splitting cube, is placed on the probe light path to split the near-parallel probe light according to preset ratio parameters. One beam is output as a reference light to the spectrometer to correct inter-pulse intensity fluctuations, and the other beam is output as the main probe light to the focusing lens group. The first focusing lens group is used to focus the main probe beam so that the input near-parallel beam illuminates the device under test at a set incident angle. The device under test is a thin-film electroluminescent device with self-emissive properties. It is placed at a preset distance in front of the focal point of the focusing lens group to ensure that the diameter of the light spot reaching the device surface is larger than the diameter of the light spot at the focal point, thereby reducing the power density of the probe light and avoiding photodegradation that causes optical damage to the device. The probe light passes through the transparent electrode, hole transport layer, light-emitting layer and electron transport layer of the device under test in sequence, and is reflected by the metal reflective electrode, returning along the original path and outputting from the surface. The second focusing lens group is used to focus and collect the main probe light reflected by the device under test; The spectrometer, including a monochromator and a CCD camera, receives reference light and reflected detection light, performs dispersion and detection, and uploads the detected spectral data to the host computer. A continuous bias power supply is used to apply a continuous constant current or constant voltage bias to the device under test throughout the measurement process. The host computer includes a front-end interface and a control backend. The front-end interface is used to collect user-input parameters and control commands, and to visualize the measurement results. The control backend includes a memory and a processor. The memory stores program modules, and the processor loads the program to execute the steps of the method described in claims 1-2 to control the pulse detection light source, spectrometer, and continuous bias power supply during the preparation stage and the timing control during the measurement stage, thereby completing the in-situ differential absorption spectroscopy measurement of the electroluminescent device.

4. The synchronous measurement device for in-situ differential absorption spectrum of an electroluminescent device according to claim 3, characterized in that, The pulse detection light source is a broadband pulse xenon lamp.

5. The synchronous measurement device for in-situ differential absorption spectrum of an electroluminescent device according to claim 3, characterized in that, The host computer control backend stores the following program modules: The trigger synchronization control module is used to generate a periodic trigger signal synchronized with the CCD frame sequence, and control the pulse detection light source to only light up within the odd-numbered frame integration window; it also outputs a timestamp signal synchronized with the CCD frame sequence to the spectrometer, which is used to align the spectral data with the real-time current-voltage characteristics of the device under test and record them on the time axis. The continuous bias power supply module is used to output control commands to the continuous bias power supply only during the measurement phase, so as to control it to apply a continuous constant current or constant voltage bias to the device under test without interrupting the device's operating state. The data processing module will combine the acquired even-numbered frame spectral data with the dark background frame I. bg,off The difference is calculated as the electroluminescence spectrum EL of the device under test at the current moment; the net probe intensity is extracted from the difference between adjacent odd-numbered and even-numbered frames of spectrum, and the differential absorption spectrum ΔA is calculated using the following formula: ΔA = -log[(I on - I off ) / (I bg,on - I bg,off )], where I on For odd-numbered detection frame strength, I off The intensity of adjacent even-numbered frames.

6. The synchronous measurement device for in-situ differential absorption spectrum of an electroluminescent device according to claim 3, characterized in that, The electroluminescent devices include quantum dot light-emitting diodes (QLEDs), organic light-emitting diodes (OLEDs), and perovskite light-emitting diodes (PeLEDs).

7. The synchronous measurement device for in-situ differential absorption spectrum of an electroluminescent device according to claim 3, characterized in that, The user-input parameters and control commands include: wavelength and on / off commands for the pulse detection light source; frame rate and on / off commands for the spectrometer; and constant current or constant voltage values ​​and on / off commands for the continuous bias power supply.

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