A method for characterizing performance and kinetics of quantum dot light emitting diodes at low temperature

Abstract

The application belongs to the field of dynamics, and specifically provides a method for comprehensively characterizing the performance and carrier dynamics of quantum dot light-emitting diodes (QLEDs) under low-temperature conditions. The method includes variable-temperature efficiency testing, variable-temperature transient electroluminescence testing, variable-temperature electric-pumping transient absorption testing, and variable-temperature transient current testing, which can independently characterize the electron and hole dynamics of QLED devices at different temperatures to systematically analyze the influence of low-temperature environments on the processes of carrier injection, transport, accumulation, and recombination. Through this characterization method, the influence of low temperature on the performance of QLEDs can be accurately evaluated, helping to optimize device design and improve the stability and working efficiency of QLEDs in extreme environments, thereby promoting the practical application of QLEDs in the fields of display and lighting.

Description

Technical Field

[0001] This invention belongs to the field of characterization methods, specifically a comprehensive characterization method for the performance and carrier dynamics of quantum dot light-emitting diodes under low-temperature conditions, which is applied to the study of the performance and carrier dynamics of quantum dot light-emitting diodes under low-temperature conditions. Background Technology

[0002] Quantum dot light-emitting diodes (QLEDs), with their advantages of high color purity, wide color gamut, and low power consumption, have shown great potential in display technology and solid-state lighting, becoming a strong competitor to next-generation display technologies. With the accelerated commercialization of QLEDs, ensuring their normal operation in various harsh environments, especially at low temperatures, is crucial for their practical application and market promotion. Low temperatures can affect the injection, transport, accumulation, and recombination processes of charge carriers in QLED devices, thereby affecting the device's luminous efficiency and stability. For example, at low temperatures, carrier mobility decreases, affecting the efficiency of carrier injection and transport; some processes requiring thermal excitation are suppressed, affecting the device's dynamic response. Therefore, comprehensively characterizing the performance and carrier dynamics of QLEDs under low-temperature conditions can not only expand their applications in extreme environments but also provide a deeper understanding of the carrier injection, transport, and recombination mechanisms from a new perspective. This will help improve device efficiency and extend its lifespan. However, current research and applications mainly focus on operation and characterization at room temperature, and the impact of low temperatures on QLED device performance has not been systematically studied. Therefore, developing a method to comprehensively characterize QLED performance and carrier dynamics under low-temperature conditions is particularly necessary. Summary of the Invention

[0003] The purpose of this invention is to provide a comprehensive characterization method for the performance and carrier dynamics of quantum dot light-emitting diodes (QLEDs) under low-temperature conditions. This method comprises four parts: low-temperature efficiency testing, low-temperature transient electroluminescence testing, low-temperature electrically pumped transient absorption testing, and low-temperature transient current testing. The low-temperature efficiency test provides the current, luminescence characteristics, and external quantum efficiency (EQE) of the QLED at different temperatures; the low-temperature transient electroluminescence test provides hole dynamics at different temperatures; the low-temperature electrically pumped transient absorption test provides electron dynamics information at different temperatures; and the low-temperature transient current test reflects the current response characteristics at different temperatures. Through these four tests, a comprehensive understanding of the performance changes and carrier dynamics characteristics of QLEDs under low-temperature conditions can be achieved.

[0004] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0005] A method for characterizing the performance and dynamics of quantum dot light-emitting diodes at low temperatures, specifically as follows:

[0006] We conducted low-temperature efficiency tests, low-temperature transient electroluminescence tests, low-temperature electric-pumped transient absorption tests, and low-temperature transient current tests on quantum dot light-emitting diodes (QLEDs). We then analyzed the results of these four tests to achieve a comprehensive characterization of QLEDs under low-temperature conditions.

[0007] The low-temperature efficiency test specifically includes:

[0008] A linear step voltage signal is output from a source meter and transmitted through a signal line to a cryogenic thermostat to illuminate the QLED device. Simultaneously, the source meter records the current flowing through the QLED, a spectrometer collects the light emitted by the QLED, and an integrating sphere system is used to measure the total luminous flux of the QLED at room temperature. The light collected by the spectrometer is added to the total luminous flux to correct the optical output of the QLED. The efficiency is calculated using the current recorded by the source meter and the corrected luminous flux.

[0009] The low-temperature transient electroluminescence test specifically includes:

[0010] The trigger signal source outputs two synchronous voltage signals. One voltage signal is transmitted to the function generator through a signal line. The function generator generates a pulse voltage signal, which is transmitted to the variable temperature sample stage through a signal line to light up the QLED device. The emission of the QLED is collected and focused by a microscope. The other voltage signal is transmitted to the time-correlated single-photon counting device through a signal line. The time-correlated single-photon counting device collects the data collected by the microscope.

[0011] The cryogenic electric pump transient absorption test is specifically as follows:

[0012] A function generator generates a trigger signal and a pulse voltage signal. The pulse voltage signal is transmitted to the cryostat via a signal line to illuminate the QLED device. The trigger signal triggers a white laser to emit white light via the signal line. Under the control of a delay device consisting of a timing card and a delay calculator, the white laser is delayed until it reaches the QLED device after the pulse voltage signal illuminates it, allowing for detection. The probe light then enters a detector spectrometer for analysis. Before the white light reaches the QLED device, it undergoes beam splitting, with one portion reaching the QLED device and the other portion entering a reference spectrometer. By comparing the data difference between the detector spectrometer and the reference spectrometer, the intensity fluctuation of the probe light is corrected.

[0013] The low-temperature transient current test specifically includes:

[0014] The function generator outputs a pulse voltage signal, which is transmitted to the cryostat via a signal line to light up the QLED device. The current response of the QLED is recorded using an oscilloscope.

[0015] The present invention has the following beneficial effects and advantages:

[0016] This invention expands the comprehensive characterization capability of QLED devices under low-temperature conditions, covering multiple aspects such as efficiency, hole and electron dynamics, and current response time. It can accurately characterize the impact of temperature on the performance of QLED devices, thus laying the foundation for their application in extreme environments. It also provides theoretical and experimental support for further improving device efficiency and lifetime. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the test method.

[0018] Figure 2 The diagram shows the efficiency-current-voltage of the QLED in Example 1 at different temperatures.

[0019] Figure 3 The image shows the electric pump transient absorption spectra of the QLED in Example 1 at different temperatures.

[0020] Figure 4 The transient electroluminescence spectra of the QLED in Example 1 at different temperatures are shown.

[0021] Figure 5 The transient current diagrams of the QLED in Example 1 at different temperatures are shown. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0023] See Figure 1 The testing method in this embodiment includes four parts: low-temperature efficiency testing, low-temperature transient electroluminescence testing, low-temperature electric-pumped transient absorption testing, and low-temperature transient current testing. Low-temperature efficiency testing provides the current, luminescence characteristics, and external quantum efficiency (EQE) of the QLED at different temperatures; low-temperature transient electroluminescence testing provides hole dynamics at different temperatures; low-temperature electric-pumped transient absorption testing provides electron dynamics information at different temperatures; and low-temperature transient current testing reflects the current response characteristics at different temperatures.

[0024] 1. The low-temperature efficiency testing section includes: a cryostat, a source meter, a fiber optic spectrometer, and an integrating sphere system. The source meter outputs a linear step voltage signal, which is transmitted through a signal line to the cryostat to illuminate the QLED device. Simultaneously, the source meter records the current response of the QLED. The QLED's emission is collected by the spectrometer, and the total luminous flux is measured at room temperature using the integrating sphere system to correct the optical output.

[0025] 2. The low-temperature transient electroluminescence testing section includes: a variable-temperature sample stage, a trigger signal source, a function generator, a microscope, and a time-correlated single-photon counting device. The trigger signal source outputs two synchronous voltage signals. One voltage signal is transmitted to the function generator via a signal line. The function generator generates a pulse voltage signal, which is then transmitted to the variable-temperature sample stage via the signal line to illuminate the QLED device. The other voltage signal is transmitted to the time-correlated single-photon counting device via the signal line. The emission from the QLED is collected and focused by the microscope, and the data is finally acquired by the time-correlated single-photon counting device.

[0026] 3. The cryogenic electric-pumped transient absorption test section includes: a cryostat, a function generator, a white laser, a timing card, a delay calculator, a reference spectrometer, and a detection spectrometer. The function generator generates a trigger signal and a pulse voltage signal. The pulse voltage signal is transmitted to the cryostat via a signal line to illuminate the QLED device. The trigger signal triggers the white laser to emit white light via the signal line. Under the control of the timing card and the delay calculator, the white laser reaches the device after the pulse voltage signal illuminates the QLED for detection. The detection light then enters the detection spectrometer for analysis. Before reaching the device, the white light is split, with one portion reaching the device and the other portion entering the reference spectrometer for calibration.

[0027] 4. The low-temperature transient current testing section includes: a cryostat, a function generator, and an oscilloscope. The function generator outputs a pulse voltage signal, which is transmitted through a signal line to the cryostat to illuminate the QLED device. The oscilloscope records the current response of the QLED.

[0028] 5. All temperature changes are achieved through a cryostat or a variable temperature sample stage, with an accuracy of 0.01K.

[0029] Low-temperature efficiency testing provides a fundamental understanding of QLED performance, while combining low-temperature transient electroluminescence testing with low-temperature electrically pumped transient absorption testing allows for precise analysis of the electron-hole dynamics within the QLED. Simultaneously, transient current testing enables the calculation of the total injected charge. This organic combination of four components allows for a comprehensive characterization of QLEDs under low-temperature conditions, providing crucial support for a deeper understanding of their performance.

[0030] See Figure 1After the equipment is connected, the source meter outputs a linear step voltage signal, which is transmitted to the cryostat via a signal line to illuminate the QLED device, while simultaneously recording the QLED's current response. The QLED's emission is collected by a spectrometer, and the total luminous flux is measured at room temperature using an integrating sphere system to correct the optical output. A trigger signal source generates two synchronous voltage signals. One is transmitted via a signal line to a function generator, which generates a pulse voltage signal, which is then transmitted via a signal line to the variable-temperature sample stage to illuminate the QLED device. The other voltage signal is transmitted to a time-correlated single-photon counter. The QLED's emission is collected and focused by a microscope, and finally, the time-correlated single-photon counter collects the data. The function generator simultaneously generates a trigger signal and a pulse voltage signal. The pulse voltage signal is transmitted via a signal line to the cryostat to illuminate the QLED device; the trigger signal is used to trigger the white laser to emit white light. Under the control of the timing card and delay calculator, the white laser illuminates the device after a delay following the pulse voltage signal illuminating the QLED. The probe light then enters the detector spectrometer for analysis. Before reaching the device, a portion of the white light is split and sent to a reference spectrometer for calibration. The pulse voltage signal is output by a function generator and transmitted through a signal line to a cryostat to illuminate the QLED. The current response is recorded by an oscilloscope. Temperature changes are achieved through a cryostat or a variable-temperature sample stage with an accuracy of 0.01K. All data is acquired and saved by the program.

[0031] Example 1:

[0032] The QLED devices used in the experiment were provided by the collaborating team, and the device structure was ITO / PEDOT:PSSS / TFB / QD / ZnMgO / Al. Figure 2 The EQE-voltage curves of QLEDs at different temperatures are shown, and the results indicate that the external quantum efficiency (EQE) decreases and the turn-on voltage increases at low temperatures. Figure 3 The transient absorption spectra of QLEDs under electric pumping at different temperatures are shown. The signal at 528 nm is enhanced under low temperature conditions, indicating that the carrier injection is more unbalanced and electrons accumulate in the emitting layer. Figure 4 The transient electroluminescence spectra of QLEDs at different temperatures show that the fluorescence intensity decreases and the injection rate slows down at low temperatures, indicating that low temperatures significantly reduce the efficiency of hole injection into the emissive layer. Figure 5 The transient current plots of QLED at different temperatures are shown. The operating current decreases at low temperatures, and the injected charge decreases, indicating that electron accumulation is not due to increased charge injection.

Claims

1. A method for characterizing the performance and dynamics of quantum dot light-emitting diodes at low temperatures, characterized in that, Specifically: We conducted low-temperature efficiency tests, low-temperature transient electroluminescence tests, low-temperature electric-pumped transient absorption tests, and low-temperature transient current tests on quantum dot light-emitting diodes (QLEDs). We then analyzed the results of these four tests to achieve a comprehensive characterization of QLEDs under low-temperature conditions.

2. The method for characterizing the performance and dynamics of a quantum dot light-emitting diode at low temperature according to claim 1, wherein the low-temperature efficiency test specifically comprises: A linear step voltage signal is output from a source meter and transmitted through a signal line to a cryogenic thermostat to illuminate the QLED device. Simultaneously, the source meter records the current flowing through the QLED, a spectrometer collects the light emitted by the QLED, and an integrating sphere system is used to measure the total luminous flux of the QLED at room temperature. The light collected by the spectrometer is added to the total luminous flux to correct the optical output of the QLED. The efficiency is calculated using the current recorded by the source meter and the corrected luminous flux.

3. The method for characterizing the performance and dynamics of a quantum dot light-emitting diode at low temperature according to claim 1, wherein the low-temperature transient electroluminescence test specifically comprises: The trigger signal source outputs two synchronous voltage signals. One voltage signal is transmitted to the function generator through a signal line. The function generator generates a pulse voltage signal, which is transmitted to the variable temperature sample stage through a signal line to light up the QLED device. The emission of the QLED is collected and focused by a microscope. The other voltage signal is transmitted to the time-correlated single-photon counting device through a signal line. The time-correlated single-photon counting device collects the data collected by the microscope.

4. The method for characterizing the performance and dynamics of a quantum dot light-emitting diode at low temperature according to claim 1, wherein the low-temperature electrically pumped transient absorption test specifically comprises: A function generator generates a trigger signal and a pulse voltage signal. The pulse voltage signal is transmitted to the cryostat via a signal line to illuminate the QLED device. The trigger signal triggers a white laser to emit white light via the signal line. Under the control of a delay device consisting of a timing card and a delay calculator, the white laser is delayed until it reaches the QLED device after the pulse voltage signal illuminates it, allowing for detection. The probe light then enters a detector spectrometer for analysis. Before the white light reaches the QLED device, it undergoes beam splitting, with one portion reaching the QLED device and the other portion entering a reference spectrometer. By comparing the data difference between the detector spectrometer and the reference spectrometer, the intensity fluctuation of the probe light is corrected.

5. The method for characterizing the performance and dynamics of a quantum dot light-emitting diode at low temperature according to claim 1, wherein the low-temperature transient current test specifically comprises: The function generator outputs a pulse voltage signal, which is transmitted to the cryostat via a signal line to light up the QLED device. The current response of the QLED is recorded using an oscilloscope.

Images