Detection method and detection system of quantum dot light-emitting device

Abstract

The invention discloses a detection method and a detection system for a quantum dot light-emitting device. The detection method comprises the following steps: providing a to-be-measured sub-dot light-emitting device; applying voltage and illumination to the to-be-measured sub-point light-emitting device; obtaining a fluorescence intensity-time relationship of the to-be-measured sub-point light-emitting device after power failure; and determining the charge accumulation state in the to-be-measured sub-point light-emitting device according to the fluorescence light-emitting intensity-time relationship. According to the technical scheme, whether charge accumulation exists in the light-emitting layer of the to-be-measured sub-point light-emitting device or not and the charge accumulation degree can be judged according to the change condition of the light-emitting intensity of the fluorescence emitted by the to-be-measured light-emitting device after power failure; therefore, whether the cause of brightness decay of the device comprises charge accumulation in the light-emitting layer can be accurately analyzed, and a guiding thought is provided for researching and optimizing the device.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor devices, and particularly to a detection method and a detection system for a quantum dot light-emitting device. Background Art

[0002] A quantum dot light-emitting device is a device formed by stacking multiple layers of p-type or n-type semiconductor materials. The device structure is generally anode / hole functional layer / quantum dot light-emitting layer / electron functional layer / cathode. Among them, electrons are injected from the cathode through the electron functional layer into the light-emitting layer, and at the same time, holes are transmitted from the anode through the hole functional layer to the light-emitting layer. Electrons and holes generate excitons and radiatively recombine to emit light. When the electron injection and hole injection in the light-emitting device are unbalanced, charge accumulation will occur in the light-emitting layer, resulting in the electrons and holes injected into the light-emitting layer being prone to undergo Auger recombination when forming excitons, thereby affecting the light-emitting efficiency and brightness.

[0003] During the actual use of the light-emitting device, the brightness will gradually decay. This brightness decay may be caused by the attenuation of the hole functional layer, the quantum dot light-emitting layer, or the electron functional layer materials themselves, or may be caused by charge accumulation in the hole functional layer, the quantum dot light-emitting layer, or the electron functional layer.

[0004] Therefore, measuring or characterizing the charge accumulation situation in the quantum dot light-emitting device is of great significance for studying the brightness decay of the device. Summary of the Invention

[0005] In view of this, the present application provides a detection method and a detection system for a quantum dot light-emitting device.

[0006] The embodiments of the present application are implemented as follows:

[0007] In a first aspect, the embodiments of the present application provide a detection method for a quantum dot light-emitting device, including the following steps:

[0008] Provide a quantum dot light-emitting device to be measured;

[0009] Apply a voltage and light to the quantum dot light-emitting device to be measured;

[0010] Obtain the fluorescence emission intensity-time relationship of the quantum dot light-emitting device to be measured after power-off;

[0011] Determine the charge accumulation state in the quantum dot light-emitting device to be measured according to the fluorescence emission intensity-time relationship.

[0012] Optionally, in some embodiments of the present application, the quantum dot light-emitting device to be measured includes a light-emitting layer;

[0013] The steps of determining the charge accumulation state in the quantum dot light-emitting device to be measured according to the fluorescence emission intensity-time curve include:

[0014] The steps of obtaining the fluorescence emission intensity-time relationship of the quantum dot light-emitting device to be measured after power-off include:

[0015] Stop applying voltage to the quantum dot light-emitting device to be measured, obtain the fluorescence emission intensity varying with time of the quantum dot light-emitting device to be measured after power-off, and determine the fluorescence emission intensity-time relationship.

[0016] Optionally, in some embodiments of the present application, the steps of determining the charge accumulation state in the quantum dot light-emitting device to be measured according to the fluorescence emission intensity-time relationship further include:

[0017] Obtain the maximum change value of the fluorescence emission intensity of the fluorescence emission intensity-time curve. The larger the maximum change value of the fluorescence emission intensity, the higher the charge accumulation degree in the quantum dot light-emitting device to be measured.

[0018] Optionally, in some embodiments of the present application, when there are multiple quantum dot light-emitting devices to be measured;

[0019] The detection method of the quantum dot light-emitting device further includes:

[0020] After determining the charge accumulation states in multiple quantum dot light-emitting devices to be measured, compare the charge accumulation degrees of multiple quantum dot light-emitting devices according to the maximum change values of the fluorescence emission intensities of multiple quantum dot light-emitting devices to be measured.

[0021] Optionally, in some embodiments of the present application, after the step of comparing the charge accumulation degrees of multiple quantum dot light-emitting devices according to the maximum change values of the fluorescence emission intensities of multiple quantum dot light-emitting devices to be measured, further include:

[0022] Obtain a first device, where the first device is the quantum dot light-emitting device with the smallest maximum change value of the fluorescence emission intensity among multiple quantum dot light-emitting devices to be measured;

[0023] Obtain the light-emitting layer information of the first device.

[0024] Optionally, in some embodiments of the present application, the light-emitting layer information includes one or more of the light-emitting layer thickness, the type of light-emitting layer material, and the size of the light-emitting layer material.

[0025] Optionally, in some embodiments of the present application, power off after applying the voltage for a preset time to stop applying the voltage, and the preset time is 3 to 30 min.

[0026] Optionally, in some embodiments of the present application, the voltage is a pulsed constant current voltage; and / or,

[0027] the light during illumination is pulsed monochromatic light; and / or,

[0028] during illumination, the angle between the light and the light-emitting surface of the quantum dot light-emitting device to be measured is 30° to 45°; and / or,

[0029] The fluorescence emission intensity-time relationship is obtained through a lock-in amplifier and a detector.

[0030] Optionally, in some embodiments of the present application, the duty cycle of the pulsed constant current voltage is 20% to 50%; and / or,

[0031] the frequency of the chopper is A, where A satisfies: A > 200 Hz, and A / 50 = n, and n is a non-integer; and / or,

[0032] The pulsed monochromatic light is monochromatic light modulated by a chopper.

[0033] In a second aspect, the present application provides a detection system for a quantum dot light-emitting device, the detection system comprising:

[0034] a power supply for applying a voltage to the quantum dot light-emitting device to be measured;

[0035] a light providing device for emitting light to the quantum dot light-emitting device to be measured; and,

[0036] an acquisition circuit structure for acquiring the fluorescence emission signal emitted by the quantum dot light-emitting device to be measured and obtaining the fluorescence emission intensity-time relationship of the quantum dot light-emitting device to be measured.

[0037] Optionally, in some embodiments of the present application, the light providing device includes a light source, a monochromator, and a chopper disposed on the light-emitting side of the light source, and the monochromator and the chopper are disposed in sequence along the light transmission direction; and / or,

[0038] the power supply is a pulsed constant current power supply; and / or,

[0039] the acquisition circuit structure includes a resistor and a detector connected in series through a wire, and a lock-in amplifier connected in parallel with the resistor; and / or,

[0040] The detection system further includes a control module, and the power supply, the light providing device, and the acquisition circuit structure are all electrically connected to the control module.

[0041] Optionally, in some embodiments of the present application, the resistance value of the resistor is 50 to 5000 Ω; and / or,

[0042] The duty cycle of the pulsed constant-current voltage output by the pulsed constant-current power supply is 20% to 50%; and / or,

[0043] The frequency of the chopper is A, and A satisfies: A > 200 Hz, and A / 50 = n, where n is a non-integer.

[0044] According to the technical solution of the present application, based on the change in the luminous intensity of the fluorescence emitted by the device under test after power-off, it can be determined whether there is charge accumulation in the light-emitting layer of the quantum dot light-emitting device to be measured and the degree of charge accumulation. Thus, it can be accurately analyzed whether the reason for the brightness attenuation of the device includes charge accumulation in the light-emitting layer, providing a guiding idea for researching and optimizing the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0046] Figure 1 is a schematic flowchart of a method for detecting a quantum dot light-emitting device provided by an embodiment of the present application;

[0047] Figure 2 is a schematic structural diagram of a detection system for a quantum dot light-emitting device provided by an embodiment of the present application;

[0048] Figure 3 is a fluorescence luminous intensity-time curve graph of the QLED device under test in Embodiment 1;

[0049] Figure 4 is a fluorescence luminous intensity-time curve graph of the QLED device under test in Embodiment 2;

[0050] Figure 5 is a fluorescence luminous intensity-time curve graph of the QLED device under test in Embodiment 3;

[0051] Figure 6 is a comparative graph of fluorescence luminous intensity-time curves of the first device under test, the second device under test, and the third device under test in Embodiment 4;

[0052] Reference numerals: 1 - light source; 2 - monochromator; 3 - chopper; 4 - modulated pulsed excitation light; 5 - substrate; 6 - anode; 7 - hole injection layer; 8 - hole transport layer; 9 - quantum dot light-emitting layer; 10 - electron transport layer; 11 - cathode; 12 - power supply; 13 - reflected light; 14 - emitted PL; 15 - detector; 16 - resistor; 17 - lock-in amplifier; 100 - quantum dot light-emitting device to be measured; 101 - light-emitting surface. Detailed implementation manners

[0053] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Apparently, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present application. In addition, it should be understood that the specific implementation manners described herein are only used to illustrate and explain the present application, and are not used to limit the present application. In the present application, unless otherwise stated, the orientation terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. In addition, in the description of the present application, the term "including" means "including but not limited to". The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0054] In the present application, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, or B exists alone. Wherein A and B may be singular or plural.

[0055] In this application, "at least one" means one or more, and "a plurality" means two or more. "At least one kind", "at least one of the following items" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0056] In a first aspect, an embodiment of this application provides a detection method for a quantum dot light - emitting device, which can be used to detect the charge accumulation in the quantum dot light - emitting device 100 to be measured and study the reasons for the attenuation of the device brightness or lifetime.

[0057] As Figure 2 shown, the quantum dot light - emitting device 100 to be measured (hereinafter referred to as the device to be measured) includes a cathode 11, a functional film layer, and an anode 6 arranged in layers. The functional film layer includes, but is not limited to, a quantum dot light - emitting layer 9. The material of the quantum dot light - emitting layer 9 uses common quantum dot light - emitting materials in the art, such as single - structure quantum dots, core - shell structure quantum dots, and so on. In some embodiments, the functional film layer may further include carrier functional layers, such as a hole functional layer and / or an electron functional layer. Among them, the hole functional layer is a functional layer that promotes hole transport and is arranged between the quantum dot light - emitting layer 9 and the anode 6. The hole functional layer may include, but is not limited to, one or both of a hole transport layer 8 and a hole injection layer 7. When the hole functional layer includes a hole transport layer 8 and a hole injection layer 7, the hole injection layer 7 is located between the hole transport layer 8 and the anode 6. Similarly, the electron transport layer 10 is a functional layer that promotes electron transport and is arranged between the quantum dot light - emitting layer 9 and the cathode 11. The electron functional layer may include, but is not limited to, one or both of an electron transport layer 10 and an electron injection layer. When the electron functional layer includes an electron transport layer 10 and an electron injection layer, the electron injection layer is located between the electron transport layer 10 and the anode 6.

[0058] In some embodiments, the quantum dot light-emitting device 100 to be measured further includes a substrate 5, which can also be referred to as a substrate, and the above-mentioned film layer structure is disposed on one side of the substrate 5. The substrate 5 can be a rigid substrate 5 or a flexible substrate 5. The rigid substrate 5 can be a ceramic material or various glass materials, etc. The flexible substrate 5 can be formed of materials such as polyimide film (PI) and its derivatives, polyethylene naphthalate (PEN), phosphoenolpyruvate (PEP), or polyphenylene ether resin. In one embodiment, the material of the substrate 5 includes one or a combination of more of glass, silicon wafer, polycarbonate, polymethyl methacrylate, polyethylene terephthalate, polyethylene naphthalate, polyamide, and polyethersulfone.

[0059] The quantum dot light-emitting device 100 to be measured can be a forward light-emitting device or an inverted light-emitting device. When the device is a forward light-emitting device, the substrate 5 is bonded to the side of the anode 6 away from the quantum dot light-emitting layer 9. When the device is an inverted light-emitting device, the substrate 5 is bonded to the side of the cathode 11 away from the quantum dot light-emitting layer 9.

[0060] The method of the present application is applicable to quantum dot light-emitting devices with any structure and any film layer material.

[0061] Please refer to Figure 1 , the detection method of the quantum dot light-emitting device includes the following steps:

[0062] S10, providing a quantum dot light-emitting device 100 to be measured;

[0063] S20, applying a voltage and light to the quantum dot light-emitting device 100 to be measured;

[0064] S30, powering off to stop applying the voltage, and obtaining the fluorescence emission intensity-time relationship of the quantum dot light-emitting device 100 after powering off;

[0065] S40, determining the charge accumulation state in the quantum dot light-emitting device 100 to be measured according to the fluorescence emission intensity-time relationship.

[0066] During electroluminescence, the source of the change in brightness is relatively complex, such as material damage, change in injection barrier, etc. Therefore, there are many reasons for the brightness attenuation of the light-emitting device, including but not limited to the attenuation of the material of the quantum dot light-emitting layer 9 itself, the attenuation of the material of the carrier functional layer itself, and the possible charge accumulation in the carrier functional layer or the quantum dot light-emitting layer 9. Therefore, when studying whether the reason for the brightness attenuation of the device is caused by charge accumulation in the light-emitting layer, it is necessary to exclude as many other possible factors as possible.

[0067] In the method provided by the embodiments of the present application, a voltage is first applied to the device under test to cause charge accumulation inside the device. At this time, if the applied external voltage is stopped, the accumulated charges in the device will form a reverse flowing current. However, if only the presence of a reverse current is examined, it is impossible to distinguish which functional film layer among the carrier functional layer and the light-emitting layer the charge accumulation originates from. Among the functional layer film materials, only quantum dot light-emitting materials exhibit PL. If charges accumulate in the light-emitting layer, the accumulated charges will affect the exciton recombination of the quantum dot light-emitting materials and affect the PL intensity. Based on this, observing the change in PL intensity can clearly characterize the change in the recombination efficiency in the QD, thereby excluding the influence of charge accumulation in the carrier function and determining whether charge accumulation has occurred in the light-emitting layer of the device under test and the degree of charge accumulation.

[0068] According to the technical solution of the present application, based on the change in the emission intensity of the fluorescence emitted by the light-emitting device under test after power-off, it is possible to determine whether there is charge accumulation in the light-emitting layer of the quantum dot light-emitting device 100 to be measured and the degree of charge accumulation. Thus, it can be analyzed whether the reason for the brightness attenuation of the device includes charge accumulation in the light-emitting layer, providing a guiding idea for researching and optimizing the device structure, film materials, etc. The detection method of the present application can accurately evaluate charge accumulation, can identify which film layer the charge accumulation specifically originates from, can also evaluate the degree of charge accumulation to a certain extent, and can avoid the interference of other factors such as charge accumulation in the carrier functional layer and attenuation of each film material, better judging the reason for the brightness attenuation of the device, and having high accuracy in judging the reason for the brightness attenuation of the device.

[0069] In some embodiments, step S30 can be implemented through the following steps:

[0070] S31, Stop applying voltage to the quantum dot light-emitting device to be measured, obtain the fluorescence emission intensity of the quantum dot light-emitting device to be measured that changes with time after power-off, and determine the fluorescence emission intensity-time relationship.

[0071] By obtaining the fluorescence emission intensity of the quantum dot light-emitting device 100 after power-off, a change curve of the fluorescence emission intensity and time is plotted, which is named the fluorescence emission intensity-time curve.

[0072] In some embodiments, step S40 can be implemented through the following steps:

[0073] S41, When the fluorescence emission intensity increases as time goes by, it is determined that there is charge accumulation in the light-emitting layer.

[0074] Under light illumination conditions, the quantum dots are excited to generate outgoing PL14. When there is charge accumulation in the device, the accumulated charges affect exciton recombination, resulting in a decrease in the PL intensity, as Figures 3 to 5As shown, in the collected fluorescence intensity-time curve, the PL intensity shows an upward trend since power-off until the curve levels off, at which point the PL intensity basically no longer changes. Correspondingly, during actual detection, when the collected fluorescence intensity-time curve shows an upward trend after power-off, it indicates that there is charge accumulation in the light-emitting layer of the light-emitting device to be measured.

[0075] During the detection process, from the start of power-off until the curve levels off, the maximum value of the change in PL intensity is defined as the maximum change value of fluorescence intensity. For example, in some embodiments, at the start of power-off, the PL intensity is the minimum, and the PL intensity at this time is denoted as PL min , when the PL intensity rises to the point where the curve levels off, the PL intensity reaches the maximum value, and the PL intensity at this time is denoted as PL max , PL max and PL min The difference between them is the maximum change value of fluorescence intensity. The maximum change value of fluorescence intensity reflects the degree to which exciton recombination is affected by accumulated charges. Therefore, the degree of charge accumulation in the quantum dot light-emitting device 100 to be measured can be evaluated based on the maximum change value of fluorescence intensity.

[0076] Specifically, step S40 may further include: the greater the maximum change value of fluorescence intensity, the higher the degree of charge accumulation in the quantum dot light-emitting device 100 to be measured.

[0077] Furthermore, in some embodiments, there are multiple quantum dot light-emitting devices 100 to be measured. For this situation, the detection method for the quantum dot light-emitting devices further includes:

[0078] S50, after determining the charge accumulation states in the multiple quantum dot light-emitting devices 100 to be measured, obtaining the maximum change values of fluorescence intensity of the multiple quantum dot light-emitting devices 100 to be measured;

[0079] S60, comparing the degrees of charge accumulation of the multiple quantum dot light-emitting devices 100 based on the maximum change values of fluorescence intensity of the multiple quantum dot light-emitting devices 100 to be measured.

[0080] In actual application, the detection method provided in this article can be used to detect multiple light-emitting devices to be tested respectively, so as to collect the fluorescence intensity-time curves of the multiple light-emitting devices to be tested, and obtain the maximum change values of the fluorescence intensity of the multiple light-emitting devices to be tested. In this way, according to the magnitudes of the maximum change values of the fluorescence intensity, the charge accumulation degrees of the multiple light-emitting devices to be tested can be sorted. Among them, the higher the maximum change value of the fluorescence intensity of the light-emitting device to be tested, the higher the charge accumulation degree. For example, in a specific embodiment, there are three quantum dot light-emitting devices 100 to be measured, which are respectively named the first device to be tested, the second device to be tested, and the third device to be tested. The detection steps for the devices in this embodiment are as follows: (1) Apply voltage and light to the first device to be tested; cut off the power to stop applying the voltage, and obtain the fluorescence intensity-time curve of the first device to be tested after power-off; according to the fluorescence intensity-time curve, obtain the maximum change value of the fluorescence intensity of the first device to be tested, denoted as the first change value; (2) Apply voltage and light to the second device to be tested; cut off the power to stop applying the voltage, and obtain the fluorescence intensity-time curve of the second device to be tested after power-off; according to the fluorescence intensity-time curve, obtain the maximum change value of the fluorescence intensity of the second device to be tested, denoted as the second change value; (3) Apply voltage and light to the third device to be tested; cut off the power to stop applying the voltage, and obtain the fluorescence intensity-time curve of the third device to be tested after power-off; according to the fluorescence intensity-time curve, obtain the maximum change value of the fluorescence intensity of the third device to be tested, denoted as the third change value; (4) Compare the first change value, the second change value, and the third change value, and sort the charge accumulation degrees of the first device to be tested, the second device to be tested, and the third device to be tested according to the magnitudes of the three change values.

[0081] In some embodiments, after the step of comparing the charge accumulation degrees of the multiple quantum dot light-emitting devices 100 according to the maximum change values of the fluorescence intensity of the multiple quantum dot light-emitting devices 100, the method further includes: obtaining a first device, where the first device is the quantum dot light-emitting device 100 among the multiple quantum dot light-emitting devices 100 that has the smallest maximum change value of the fluorescence intensity; obtaining the light-emitting layer information of the first device.

[0082] The first device has the smallest maximum change value of the fluorescence intensity, indicating that the charge accumulated in its light-emitting layer is the least, and its light-emitting layer design is better and not prone to charge accumulation. Based on this, by collecting the information of the light-emitting layer of the first device, it can be used to design a light-emitting device with small charge accumulation and obtain a device with high luminous efficiency and long life.

[0083] Among them, the light-emitting layer information includes one or more of the light-emitting layer thickness, the type of light-emitting layer material, and the size of the light-emitting layer material. Generally, the material of the light-emitting layer is a quantum dot light-emitting material. The type of the light-emitting layer material may include, but is not limited to, the chemical formula of the quantum dot light-emitting material (such as CdS, CdZnSe, CdZnS, CdSe / ZnS, CdSe / ZnSe / ZnS, ZnSe / ZnS, etc.), the type of ligand connected to the surface of the quantum dot (such as oleic acid, oleylamine, etc.), or the additive material that may be doped in the light-emitting layer, etc. The size of the light-emitting layer material may be the average particle size, the hydrated particle size, etc.

[0084] To simulate the device working state, after applying the voltage for a preset time, the power is cut off to stop applying the voltage. The preset time is greater than or equal to 3 min. In some embodiments, the preset time may be 3 - 30 min, such as 3 - 5 min, 3 - 8 min, 3 - 10 min, 3 - 15 min, 3 - 20 min, 3 - 25 min, 3.5 - 12 min, 4.5 - 15 min, 5.5 - 18 min, 6 - 25 min, 10 - 20 min, etc. Specifically, the preset time may be 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 15 min, 20 min, 25 min, 30 min, and the values between any two of the above. For a device that may have charge accumulation after working for a period of time, controlling the power-on time within the above range can simulate the device working condition, effectively charge the light-emitting device to be tested, so as to simulate the possible charge distribution in the working scenario of the device, making the charge accumulation situation inside the device to be tested representative.

[0085] In some embodiments, to exclude the attenuation of the quantum dot material itself from the reasons for the brightness or lifetime attenuation of the device and improve the accuracy and precision of the detection results, the voltage is a pulsed constant current voltage. Compared with direct current, the pulsed constant current voltage can be powered on intermittently slowly, avoiding the damage to the quantum dot light-emitting material caused by the power-on itself, making the detection results more accurate.

[0086] In some embodiments, the duty cycle of the pulsed constant current voltage is 20% - 50%; for example, it may be 20%, 25%, 30%, 35%, 40%, 45%, 50%, and the values between any two of the above. The duty cycle refers to the proportion of the power-on time in the total time of the applied pulsed constant current voltage. Controlling the duty cycle within the above range helps to further reduce the impact of the current on the quantum dot light-emitting material, reduce the influence of the power-on on the quantum dot material, and further improve the accuracy of the detection results.

[0087] The illumination in step S20 is provided by light source 1 and is used to excite the luminescent device under test to emit light. The light can be light provided by any common light source 1, including but not limited to composite light sources such as xenon lamps, sodium lamps, and mercury lamps.

[0088] To ensure that the device continuously emits PL, during the experiment, it is necessary to continuously irradiate the luminescent device under test with excitation light; specifically, the device under test is irradiated with light simultaneously with or before applying the voltage, and the light irradiation is stopped until the fluorescence emission intensity-time curve collected tends to be horizontal.

[0089] To avoid interference from reflected light 13, in some embodiments, when illuminating, the angle between the light and the light-emitting surface 101 of the quantum dot luminescent device 100 to be measured is θ, and θ is 30° to 45°, for example, it can be 30°, 31°, 32°, 33°, 34°, 35°, 36°, 37°, 38°, 39°, 40°, 41°, 42°, 43°, 44°, 45°, and values between any two of the above. Controlling the incident angle θ within the above range can, on the one hand, avoid total reflection, and on the other hand, make the reflected light 13 avoid the detector 15, avoiding the interference of the reflected light 13, which helps to improve the accuracy of the detection result. It can be understood that the light-emitting surface 101 refers to a plane parallel to the surface on the light-emitting side of the device. For example, in some embodiments, when the light passes through the anode 6 and the substrate 5 of the device and emits, the plane where the surface of the substrate 5 facing away from the anode 6 is located or parallel to is the light-emitting surface 101.

[0090] In some embodiments, the detection step can be carried out in a light-shielded environment to avoid the influence of natural light.

[0091] In other embodiments, the light during illumination is discontinuous monochromatic light. The discontinuous monochromatic light is a discontinuous monochromatic light with bright and dark changes, which is different from continuous light indoors or outdoors (such as natural light, light from lighting equipment, etc.). The emitted PL14 excited by this light also has discontinuous characteristics. In this way, when the detector 15 collects the optical signal, it can avoid the interference of continuous light. In this way, when performing the detection step, there is no need to perform special protection and shielding on the light, reducing the detection difficulty, reducing the influence of interfering light, and improving the result accuracy. For example, the light during illumination can be pulsed monochromatic light. Specifically, the light can be monochromatic light modulated by the chopper 3. The light is processed into monochromatic light and then modulated by the chopper 3 into discontinuous modulated pulsed excitation light 4. The modulated pulsed excitation light 4 has a specific frequency, making the emitted PL14 more characteristic and can be collected more accurately.

[0092] During actual detection, the fluorescence intensity-time curve of the to-be-measured quantum dot light-emitting device 100 after power-off can be obtained through the lock-in amplifier 17 and the detector 15. In some embodiments, the light during illumination is monochromatic light modulated by the chopper 3, and the lock-in amplifier 17 can demodulate the optical signal with a specific frequency, so as to quickly and accurately characterize the change process of PL after power-off.

[0093] In some embodiments, the frequency of the chopper 3 is A, and A satisfies: A > 200 Hz, and A / 50 = n, where n is a non-integer. Controlling the frequency of the chopper 3 to be greater than 200 Hz and avoiding multiples of 50 Hz can avoid coupling noise and help improve the accuracy of the detection result. It can be understood that the demodulation frequency of the lock-in amplifier 17 is consistent with the frequency of the chopper 3, so that the signal can be accurately demodulated.

[0094] In a second aspect, the present application also proposes a detection system for a quantum dot light-emitting device. Please refer to Figure 2 , the detection system includes a power supply 12, a light providing device, and an acquisition circuit structure. The detection system has a station for placing the to-be-measured quantum dot light-emitting device 100. During detection, the to-be-detected light-emitting device is placed on the station. The power supply 12 is used to connect the to-be-detected light-emitting device and apply a voltage to the to-be-detected light-emitting device. The light providing device is used to emit light to the to-be-detected light-emitting device. The acquisition circuit structure is used to collect the fluorescence emission signal emitted by the to-be-measured quantum dot light-emitting device 100 and obtain the fluorescence intensity-time curve of the to-be-measured quantum dot light-emitting device 100.

[0095] Using the detection system can conveniently and quickly execute the above detection method, accurately detect the charge accumulation in the to-be-measured quantum dot light-emitting device 100, and study the reasons for the attenuation of the device brightness or lifetime.

[0096] In some embodiments, the light providing device includes a light source 1, a monochromator 2, and a chopper 3. The light source 1 has a light-emitting side, and the monochromator 2 and the chopper 3 are arranged on the light-emitting side of the light source 1, and the monochromator 2 and the chopper 3 are arranged in sequence along the light transmission direction, that is, in the light transmission direction, the monochromator 2 and the chopper 3 are sequentially arranged between the light source 1 and the station.

[0097] Among them, the light source 1 can be any common composite light source, including but not limited to xenon lamps, sodium lamps, mercury lamp composite light sources, etc.

[0098] Among them, the monochromator 2 is a device that decomposes the composite light of wide-band luminescence (peak width of several hundred to thousands of nanometers) into narrow-band monochromatic light with a half-peak width of 10 to 30nm, including but not limited to the common monochromatic instrument with multi-level gratings and slits as the core of the light splitting. It can be understood that the monochromatic light is used to excite the quantum dot luminescent material, and its excitation wavelength can be selected as a wavelength that is compatible with the quantum dot luminescent material to be excited. Specifically, its excitation wavelength can meet the following conditions: the wavelength energy of the excitation quantum dot luminescent material is greater than the energy required for the band gap transition of the quantum dot luminescent material, that is, the excitation wavelength is less than the band gap of the quantum dot luminescent material. In order to ensure that the quantum dot luminescent material is fully excited or has a good fluorescence intensity, in some embodiments, the excitation wavelength of the monochromator 2 is selected as λ, λ is less than the band gap of the quantum dot luminescent material to be excited, and the difference between the two is about 30nm.

[0099] Among them, the chopper 3 is a device that divides common continuous light into intermittent non-continuous light with a certain frequency. The light modulated by the chopper 3 has a specific frequency. When the light-emitting device to be tested is excited, it will emit fluorescence of the corresponding frequency or generate an electrical signal with a certain frequency response.

[0100] When installing the light providing device, the installation position of the light providing device can be adjusted to meet the following conditions: ensure that the excitation light output from the light providing device is incident on the light-emitting device to be tested on the workstation with an incident angle of 30° to 45° to avoid interference from the reflected light 13.

[0101] The power supply 12 can be a pulse constant voltage power supply or a pulse constant current power supply. In some embodiments, the power supply 12 is a pulse constant current power supply, which can provide a pulse constant current voltage to slowly and intermittently energize the light-emitting device to be tested, thereby avoiding the damage of the quantum dot light-emitting material by the energization itself, and making the detection result more accurate. During actual detection, the current of the pulse constant current power supply can be kept consistent with the current during the accelerated test of the device under daily working conditions, so that the light-emitting device to be tested is more representative, which helps to improve the accuracy and credibility of the detection results. In one embodiment, the current is 2mA.

[0102] In some embodiments, the duty cycle of the pulse constant current voltage is 20% to 50%; for example, it can be 20%, 25%, 30%, 35%, 40%, 45%, 50% and any value between the above two values. The duty cycle refers to the proportion of the power-on time in the applied pulse constant current voltage relative to the total time. Controlling the duty cycle within the above range helps to further reduce the impact of the current on the quantum dot luminescent material, reduce the impact of power-on on the quantum dot material, and further improve the accuracy of the detection results.

[0103] In some embodiments, the acquisition circuit structure includes a resistor 16 and a detector 15 connected in series through a wire, and a lock-in amplifier 17 connected in parallel with the resistor 16. The detector 15 is used to collect optical signals and convert the optical signals into electrical signals. The detector 15 can be any common photodetector in the art, such as a photomultiplier tube, a silicon-based diode detector, etc. In some embodiments, the detector 15 is a silicon-based diode detector, which has advantages such as high responsiveness, low cost, easy maintenance, and low stray light interference.

[0104] The lock-in amplifier 17 can demodulate and extract the amplitude and phase of the AC signal. That is, when a signal contains multiple frequencies, the lock-in amplifier 17 can extract the amplitude at the corresponding frequency in sequence according to the corresponding frequency. The lock-in amplifier 17 in this application includes but is not limited to common lock-in amplifiers for single-frequency and multi-frequency demodulation. Modulating the excitation light through the chopper 3 to make it have a specific frequency and then demodulating it with the lock-in amplifier 17 helps to quickly characterize the change process of PL after power-off, helps to more accurately capture the emitted PL14 excited by the modulated pulse excitation light 4, improves the accuracy, and at the same time enables the detection process to be carried out without a light-shielded environment, reducing the detection difficulty.

[0105] In some embodiments, the frequency of the chopper 3 is A, and A satisfies: A > 200 Hz, and A / 50 = n, where n is a non-integer. Controlling the frequency of the chopper 3 to be greater than 200 Hz and avoiding multiples of 50 Hz can avoid coupling noise and help improve the accuracy of the detection result. It can be understood that the demodulation frequency of the lock-in amplifier 17 is the same as the frequency of the chopper 3, so that the signal can be accurately demodulated.

[0106] The detector 15 generates a photocurrent signal, while the lock-in amplifier 17 demodulates the voltage amplitude signal. Therefore, a series resistor 16 is connected to the circuit of the detector 15 to better convert the signal. The resistor 16 can include but is not limited to common wire-wound resistors, carbon film resistors, metal film resistors, metal oxide resistors, etc. In some embodiments, the resistance value of the resistor 16 is 50 - 5000 Ω; for example, it can be 50 Ω, 70 Ω, 90 Ω, 100 Ω, 200 Ω, 300 Ω, 400 Ω, 500 Ω, 600 Ω, 700 Ω, 800 Ω, 1000 Ω, 2000 Ω, 3000 Ω, 4000 Ω, 5000 Ω, and values between any two of the above values. Selecting a resistor 16 with a resistance value within the above range and connecting it in series in the circuit where the detector 15 is located helps to enhance the AC signal input to the lock-in amplifier 17, improve the signal-to-noise ratio of demodulation, and at the same time avoid forming an RC oscillation circuit and affecting the current.

[0107] In some embodiments, the detection system further includes a control module (not shown in the figure), which is electrically connected to the power supply 12 and is configured to control the power supply 12 to output voltage or stop power supply. The control module can also be configured to be electrically connected to the acquisition circuit structure, and is used to control the acquisition circuit structure to acquire the fluorescence emission signal emitted by the quantum dot light-emitting device 100 to be measured after the power supply 12 stops power supply, and obtain the fluorescence emission intensity-time relationship of the quantum dot light-emitting device 100 to be measured. In addition, the control module can also be configured to be electrically connected to the light providing device, and is used to control the light providing device to emit light or stop emitting light. Among them, the specific structure of the control module and its connection relationship with the power supply 12, the acquisition circuit structure, and the light providing device can refer to common control systems in the art and will not be elaborated here.

[0108] The detection system has a high degree of automation and can perform tests accurately and quickly.

[0109] The present application will be specifically described below through specific embodiments. The following embodiments are only partial embodiments of the present application and do not limit the present application. The raw materials used in the following embodiments are all commercially available products unless otherwise specified.

[0110] Example 1

[0111] (1) Provide a QLED device to be measured. The QLED device to be measured is a bottom-emitting device, and the structure of the device is: ITO / PEDOT / TFB / G-QD / ZnO / Ag in the direction from the bottom electrode to the top electrode. Among them, the emission wavelength of G-QD is 545 nm.

[0112] The preparation method of the QLED device to be measured is as follows:

[0113] Provide a glass substrate with an ITO anode, where the thickness of the ITO anode is 50 nm; spin-coat a PEDOT:PSS solution on the anode to obtain a hole injection layer with a thickness of 25 nm; spin-coat a chlorobenzene solution of TFB (the concentration of TFB is 6.5 mg / ml) on the hole injection layer to obtain a hole transport layer with a thickness of 25 nm; spin-coat a n-hexane solution of green quantum dot material (G-QD) (the concentration of G-QD is 12 mg / ml) on the hole transport layer to obtain a light-emitting layer with a thickness of 20 nm; spin-coat an ethanol solution of ZnO (the concentration of ZnO is 20 mg / ml) on the light-emitting layer to obtain an electron transport layer with a thickness of 40 nm; evaporate an Ag electrode on the electron transport layer to obtain a cathode with a thickness of 100 nm, and obtain the QLED device to be measured.

[0114] (2) Use Figure 2The detection system shown has a resistor with a resistance value of 1000 Ω in the system. Place the QLED device to be measured in the working area, connect the anode and cathode of the device to the positive and negative electrodes of the pulsed constant current power supply respectively. At the same time, adjust the orientation of the xenon light source to control the orientation of the light providing device so that the light output from the chopper irradiates the cathode of the QLED device to be measured at an incident angle of 30°. Turn on the switches of devices such as the constant current pulse power supply, xenon light source, monochromator, chopper, detector, lock-in amplifier, etc., and adjust the parameters of each device as follows: The monochromator selects an excitation wavelength of 500 nm; the chopper frequency is selected as 317 Hz; the current amplitude of the constant current pulse power supply is selected as 2 mA, the duty cycle is selected as 40%, and the pulse energization time is selected as 3 min; after power-off, collect the change in PL until the change amplitude of PL is almost unchanged. The results are as Figure 3 shown.

[0115] As can be seen from the figure, after power-off, the excited PL of the green QLED device shows an upward trend, indicating that there is charge accumulation in its light-emitting layer.

[0116] Example 2

[0117] This example is basically the same as Example 1, except that the QLED device to be measured provided in this example is a red QLED device. Correspondingly, the light-emitting layer material in this device is changed from G-QD to R-QD (red quantum dot material), and the emission wavelength of the quantum dots is 620 nm. Correspondingly, the excitation wavelength selected by the monochromator is changed to 550 nm. Except for this, other parameters and steps remain unchanged. The results are as Figure 4 shown.

[0118] As can be seen from the figure, after power-off, the excited PL of the red QLED device shows an upward trend, indicating that there is charge accumulation in its light-emitting layer.

[0119] Example 3

[0120] This example is basically the same as Example 1, except that the QLED device to be measured provided in this example is a blue QLED device. Correspondingly, the light-emitting layer material in this device is changed from G-QD to B-QD (blue quantum dot material), and the emission wavelength of the quantum dots is 471 nm. Correspondingly, the excitation wavelength selected by the monochromator is changed to 430 nm. Except for this, other parameters and steps remain unchanged. The results are as Figure 5 shown.

[0121] As can be seen from the figure, after power-off, the excited PL of the blue QLED device shows an upward trend, indicating that there is charge accumulation in its light-emitting layer.

[0122] Comparison Figure 3 , Figure 4 and Figure 5, it can be seen that the PL change (i.e., the maximum change value of fluorescence emission intensity) caused by the charge accumulation and release in the green QLED device is about 1.15 a.u., the PL change (i.e., the maximum change value of fluorescence emission intensity) caused by the charge accumulation and release in the red QLED device is within about 1.10 a.u., and the PL change (i.e., the maximum change value of fluorescence emission intensity) caused by the charge accumulation and release in the blue QLED device is above about 1.20 a.u. Obviously, the degree of charge accumulation in the red QLED device is the lowest, the degree of charge accumulation in the blue QLED device is the highest, and the degree of charge accumulation in the green QLED device is in the middle, which basically conforms to the current understanding of the common quantum dot energy level structure or carrier injection situation, indicating that the detection method proposed in this application is accurate and reliable.

[0123] Example 4

[0124] This example is basically the same as Example 1, except that the selected QLED device to be measured in this example includes a first device to be measured, a second device to be measured, and a third device to be measured, where:

[0125] The preparation method of the first device to be measured is: operating the QLED device to be measured in Example 1 under a constant current of 2 mA until the device brightness decays to 50% of the initial brightness to obtain the first device to be measured;

[0126] The preparation method of the second device to be measured is: operating the QLED device to be measured in Example 1 under a constant current of 2 mA until the device brightness decays to 75% of the initial brightness to obtain the second device to be measured;

[0127] The preparation method of the third device to be measured is: operating the QLED device to be measured in Example 1 under a constant current of 2 mA until the device brightness reaches the maximum brightness to obtain the third device to be measured.

[0128] Referring to the detection method provided in Example 1, the PL change curves of the first device to be measured, the second device to be measured, and the third device to be measured are collected respectively. Except for this, other parameters and steps remain unchanged.

[0129] The results are as Figure 6 shown.

[0130] It can be seen from the figure that the degree of PL change of the first device to be measured is the largest, the second device to be measured is the second, and the degree of change of the third device to be measured is the smallest, indicating that when the device ages, the PL change caused by charge accumulation in the QD becomes gradually serious, and the charge accumulation situation also becomes more and more serious. Based on this, the detection method proposed in this application is well verified, that is, using the change of PL after power-off to reflect the charge accumulation situation inside the QD to characterize the degree of QD charge accumulation in the QLED is accurate and reliable.

[0131] The above has introduced in detail the technical solutions provided by the embodiments of the present application. Specific examples are used in this article to elaborate on the principles and implementation manners of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those skilled in the art, according to the idea of the present application, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A detection method for a quantum dot light-emitting device, characterized in that It includes the following steps: Provide a quantum dot light-emitting device to be measured; Apply voltage and light illumination to the quantum dot light-emitting device to be measured; Obtain the fluorescence intensity-time relationship of the quantum dot light-emitting device to be measured after power-off; Determine the charge accumulation state in the quantum dot light-emitting device to be measured according to the fluorescence intensity-time relationship.

2. The detection method according to claim 1, wherein The quantum dot light-emitting device to be measured includes a light-emitting layer; The step of obtaining the fluorescence intensity-time relationship of the quantum dot light-emitting device to be measured after power-off includes: Stop applying voltage to the quantum dot light-emitting device to be measured, obtain the time-varying fluorescence intensity of the quantum dot light-emitting device to be measured after power-off, and determine the fluorescence intensity-time relationship.

3. The detection method according to claim 2, wherein The step of determining the charge accumulation state in the quantum dot light-emitting device to be measured according to the fluorescence intensity-time relationship further includes: Obtain the maximum change value of the fluorescence intensity of the fluorescence intensity-time curve. The larger the maximum change value of the fluorescence intensity, the higher the charge accumulation degree in the quantum dot light-emitting device to be measured.

4. The detection method according to claim 3, characterized in that When there are multiple quantum dot light-emitting devices to be measured; The detection method of the quantum dot light-emitting device further includes: After determining the charge accumulation states in multiple quantum dot light-emitting devices to be measured, compare the charge accumulation degrees of multiple quantum dot light-emitting devices according to the maximum change values of the fluorescence intensities of multiple quantum dot light-emitting devices.

5. The detection method according to claim 4, wherein After the step of comparing the charge accumulation degrees of multiple quantum dot light-emitting devices according to the maximum change values of the fluorescence intensities of multiple quantum dot light-emitting devices, it further includes: Obtain a first device, where the first device is the quantum dot light-emitting device with the smallest maximum change value of the fluorescence intensity among multiple quantum dot light-emitting devices to be measured; Obtain the light-emitting layer information of the first device.

6. The detection method according to claim 5, wherein The light-emitting layer information includes one or more of the light-emitting layer thickness, the type of light-emitting layer material, and the size of the light-emitting layer material.

7. The detection method according to claim 1, characterized in that Power off after applying the voltage for a preset time to stop applying the voltage, and the preset time is 3 to 30 minutes; and / or, The voltage is a pulsed constant current voltage; and / or, The light during light illumination is pulsed monochromatic light; and / or, During light illumination, the angle between the light and the light-emitting surface of the quantum dot light-emitting device to be measured is 30° to 45°; and / or, Obtain the fluorescence intensity-time relationship through a lock-in amplifier and a detector.

8. The detection method according to claim 7, wherein The duty cycle of the pulsed constant current voltage is 20% to 50%; and / or, The frequency of the chopper is A, and A satisfies: A > 200 Hz, and A / 50 = n, where n is a non-integer; and / or, The pulsed monochromatic light is monochromatic light modulated by a chopper.

9. A detection system for a quantum dot light-emitting device, characterized in that, The detection system includes: A power supply for applying voltage to the quantum dot light-emitting device to be measured; A light providing device for emitting light to the quantum dot light-emitting device to be measured; and, An acquisition circuit structure for acquiring the fluorescence emission signal emitted by the quantum dot light-emitting device to be measured and obtaining the fluorescence intensity-time relationship of the quantum dot light-emitting device to be measured.

10. The detection system according to claim 9, characterized in that, The light providing device includes a light source, a monochromator and a chopper arranged on the light output side of the light source, and the monochromator and the chopper are arranged in sequence along the light transmission direction; and / or, The power supply is a pulsed constant current power supply; and / or, The acquisition circuit structure includes a resistor and a detector connected in series through a wire, and a lock-in amplifier connected in parallel with the resistor; and / or, The detection system further includes a control module, and the power supply, the light providing device, and the acquisition circuit structure are all electrically connected to the control module.

11. The detection system according to claim 10, characterized in that, The resistance value of the resistor is 50 to 5000 Ω; and / or, The duty cycle of the pulsed constant current voltage output by the pulsed constant current power supply is 20% to 50%; and / or, The frequency of the chopper is A, and A satisfies: A > 200 Hz, and A / 50 = n, where n is a non-integer.

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