A method for measuring organic semiconductor mobility based on transient electroluminescence

Abstract

The application discloses a method for measuring organic semiconductor mobility based on transient electroluminescence, and relates to the technical field of optoelectronic device testing. 2 The method is based on the transient electroluminescence method, and the thickness difference of the same material organic semiconductor thin film leads to the difference of transient electroluminescence time, and then the carrier mobility of the organic semiconductor thin film is calculated according to μ = |(d1-d2) d / [Δτ d ·|(V1-V2)|]. Compared with the traditional transient electroluminescence method, the method is not limited by the precondition of measuring minority carrier mobility, and the thickness of the required organic semiconductor thin film is smaller and more accurate. In addition, since the thickness difference of the organic semiconductor thin film is used to obtain the transient electroluminescence time difference, the transient electroluminescence time error caused by the interface barrier and the exciton trapping effect can be eliminated, so that the obtained carrier mobility is more accurate.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic device testing technology, and in particular to a method for measuring the mobility of organic semiconductors based on transient electroluminescence. Background Technology

[0002] Organic light-emitting diodes (OLEDs) are a technology that uses organic semiconductor thin films to emit light under an applied electric field. They have many advantages such as flexibility, thinness, high brightness, and low power consumption, and are currently widely used in smartphones, televisions, wearable devices, automotive displays, and other fields.

[0003] OLEDs are DC-driven devices. During operation, electrons and holes are injected into the OLED device from the cathode and anode, respectively. These electrons and holes are then transported to the emissive layer, recombine, and emit light. The photoelectric performance of an OLED device is closely related to the injection and transport of charge carriers. Different functional layers within the device use different materials, resulting in variations in electron and hole injection and transport. Furthermore, the unavoidable presence of defects and non-radiative recombination centers within the OLED device inevitably affects the carrier transport and recombination process. Therefore, measuring the carrier transport in the organic functional layers of an OLED plays a crucial role in assessing its photoelectric performance. Similar to inorganic semiconductor materials, mobility is the most direct performance parameter for evaluating the carrier transport capability of organic semiconductor materials.

[0004] Currently, the main methods for measuring carrier mobility in organic semiconductor materials include: time-of-flight (TOF), spatially confined current (SFC) method, injection-type transient dark current (ICD) method, and transient electroluminescence (TEE) method. Among these, the TOF method provides relatively accurate results but requires sample thicknesses on the micrometer scale, resulting in a large sample volume. While the SFC method has lower sample thickness requirements (100–300 nm), it requires ohmic injection of carriers from the electrode, a condition that is difficult to meet in practical applications. Furthermore, the results of the SFC method require data fitting, leading to some measurement error. The injection-type ICD method requires less film thickness than the TOF method, but still demands relatively high-performance equipment. The TEE method utilizes a pulsed voltage signal to excite a transient emission signal; the carrier mobility can be calculated by detecting the transient electroluminescence time. This method has relatively low equipment requirements, but its current application requires measuring minority carrier mobility. This necessitates a significant increase in the mobility of one carrier type compared to another. In this case, the majority of the driving voltage drop originates from the organic material layer under test, which has lower mobility, thus providing a more accurate voltage value for mobility calculation. Since hole mobility is generally higher than electron mobility in organic semiconductor materials, this method is significantly limited in hole mobility measurement. Furthermore, contact barriers, interface barriers, and carrier trapping effects between the organic layer and electrodes inevitably affect the driving voltage, impacting the accuracy of the voltage value for the organic material layer under test and consequently causing errors in mobility.

[0005] It is evident that existing technologies still need improvement and enhancement. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for measuring the mobility of organic semiconductors based on transient electroluminescence, which aims to solve the defects of the prior art in measuring the mobility of organic semiconductors by transient electroluminescence method, which has many testing condition restrictions and large mobility error.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for measuring the mobility of organic semiconductors based on transient electroluminescence, wherein the method includes the following steps:

[0009] Step S1. Prepare two organic electroluminescent devices. Both organic electroluminescent devices include an organic semiconductor layer to be tested. The thicknesses of the organic semiconductor layers in the two organic electroluminescent devices are set as d1 and d2, respectively, and d1 is not equal to d2. Except for the difference in the thickness of the organic semiconductor layer to be tested, the other organic layers and electrode structures of the two organic electroluminescent devices are the same.

[0010] Step S2. Based on the driving voltages V1 and V2 of the two organic electroluminescent devices under the same current density, positive rectangular pulse voltage signals with high levels of V1 and V2 and low levels of zero are applied to the two organic electroluminescent devices. The transient electroluminescence time τ of the organic electroluminescent devices with thicknesses of d1 and d2 is measured using a transient spectrometer. d1 and τ d2 The transient electroluminescence time is defined as the time corresponding to the rising edge of the transient electroluminescence signal reaching 10% intensity.

[0011] Step S3. According to τ d1 and τ d2 The transient electroluminescence time difference Δτ of organic electroluminescent devices with different thicknesses was calculated. d =|(τ d1 -τ d2 According to the organic semiconductor mobility calculation formula μ=|(d1-d2)| 2 / [Δτ d ·Calculate the mobility of the organic semiconductor material under test using |(V1-V2)|];

[0012] Step S4. According to the measurement steps S1-S3, measure the mobility of the organic semiconductor under test under different current densities, and the mobility under different electric field strengths E=|(V1-V2) / (d1-d2)| can be obtained.

[0013] In the method for measuring the mobility of organic semiconductors based on transient electroluminescence, the organic electroluminescent device sequentially comprises: an anode, a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer, and a cathode, wherein the electron transport layer or the hole transport layer is the organic semiconductor layer to be measured.

[0014] In the method for measuring the mobility of organic semiconductors based on transient electroluminescence, the thickness of the light-emitting layer is 1–10 nm.

[0015] In the method for measuring the mobility of organic semiconductors based on transient electroluminescence, the thickness of the organic semiconductor layer to be measured is 50–300 nm, and the difference between d1 and d2 is 50–200 nm.

[0016] In the method for measuring the mobility of organic semiconductors based on transient electroluminescence, when the electron transport layer is the organic semiconductor layer to be measured, the hole transport layer thickness is 50-150 nm.

[0017] In the method for measuring the mobility of organic semiconductors based on transient electroluminescence, when the hole transport layer is the organic semiconductor layer to be measured, the thickness of the electron transport layer is 30-100 nm.

[0018] In the method for measuring the mobility of organic semiconductors based on transient electroluminescence, in step S2, the high-level pulse width of the pulse voltage signal is 10–1000 μs, and the frequency is 10–10. 5 Hz.

[0019] In the method for measuring the mobility of organic semiconductors based on transient electroluminescence, in step S2, the rise time of the pulse voltage signal applied to the organic electroluminescent device is ≤50ns.

[0020] Beneficial effects:

[0021] This invention provides a method for measuring the mobility of organic semiconductors based on transient electroluminescence. This method, building upon the transient electroluminescence method, utilizes the fact that differences in the thickness of organic semiconductor films of the same material lead to different transient electroluminescence times, and then, based on μ=|(d1-d2)| 2 The carrier mobility of the organic semiconductor thin film is calculated using / [Δτd·|(V1-V2)|]. Compared to the traditional transient electroluminescence method, this method is not limited by the prerequisite of measuring minority carrier mobility and can be applied to the measurement of electron or hole mobility, thus solving the problem that the traditional transient electroluminescence method is difficult to accurately measure hole mobility. On the other hand, compared to the time-of-flight method, which requires a sample thickness on the order of micrometers, the thickness of the organic functional layer in this method is only on the order of hundreds of nanometers, requiring less sample than the time-of-flight method, thus maintaining the advantage of transient electroluminescence in measuring mobility. In addition, since the transient electroluminescence time difference is obtained by using the thickness difference of the organic semiconductor thin film, the transient electroluminescence time error caused by the interface barrier can be effectively eliminated, thereby overcoming the influence of the interface barrier between the organic semiconductor layer and the electrode, and between the organic semiconductor layers in the device under test, on the accuracy of the mobility, resulting in a more accurate carrier mobility. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the single-layer device structure and testing principle of the present invention.

[0023] Figure 2 This is a schematic diagram of the structure of an organic electroluminescent device.

[0024] Figure 3 The transient electroluminescence characteristics of the organic electroluminescent device described in Embodiment 1 of this application (Figure a shows d1 = 50 nm, Figure b shows d2 = 150 nm) under different current densities.

[0025] Figure 4 The mobility is measured under different electric field strengths in Examples 1 and 2.

[0026] Figure 5 For comparison example 1, the mobility under different electric field strengths was measured using the time-of-flight method.

[0027] In the attached figures, the following labels are used: 101, signal generator; 102, organic electroluminescent device sample with the mobility to be measured; 103, spectrometer; 104, photodetector; 105, industrial control system; 201, anode; 202, hole injection layer; 203, hole transport layer; 204, electron blocking layer; 205, light-emitting layer; 206, hole blocking layer; 207, electron transport layer; 208, electron injection layer; 209, cathode. Detailed Implementation

[0028] This invention provides a method for measuring the mobility of organic semiconductors based on transient electroluminescence. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following embodiments are provided to further illustrate the invention in detail. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0029] This invention provides a method for measuring the mobility of organic semiconductors based on transient electroluminescence (TEE). This method is an improvement on the TEE method, utilizing the fact that differences in the thickness of organic semiconductor layers of the same material lead to different transient electroluminescence times, thereby calculating the carrier mobility of the organic semiconductor layer. Existing TEE methods measure the mobility of organic semiconductor materials by applying a rectangular pulse voltage to the organic light-emitting device (OLED) under test, causing it to generate a mobility-dependent transient electroluminescence signal. Because organic semiconductor materials have low carrier mobility, there is a delay time between the start of luminescence and the applied pulse voltage, i.e., the transient electroluminescence time (t). d The voltage v across the organic semiconductor thin film under test, the thickness d of the organic semiconductor thin film, and the transient electroluminescence time t are obtained. d According to the formula

[0030]

[0031] The mobility of the organic semiconductor thin film under test can then be obtained. However, the prerequisite for accurately obtaining the voltage across the organic semiconductor thin film under test using the above method is that the mobility under test is assumed to be much lower than another mobility of the device. For example, if the mobility under test is electron mobility, then the hole mobility of the device needs to be much higher than the electron mobility. In this case, the voltage across the organic semiconductor thin film under test is approximately equal to the driving voltage of the device.

[0032] In the method for measuring the mobility of organic semiconductors based on transient electroluminescence described in this invention, based on the transient electroluminescence method, it utilizes two organic semiconductor layers of the same material but different thicknesses under the same current density. The thicker organic semiconductor layer can be considered as a thinner organic semiconductor layer connected in series with another organic semiconductor layer whose thickness is the difference between the two. Therefore, the formula for calculating the mobility of the organic semiconductor can be obtained as follows:

[0033] μ=|(d1-d2)| 2 / [Δτ d ·|(V1-V2)|] (2)

[0034] In formula (2), Δτ d The transient electroluminescence time difference between two organic semiconductor layers with different thicknesses can be obtained by measuring the transient electroluminescence time of the two organic semiconductor layers with different thicknesses respectively. d1 and d2 are the thicknesses of the two organic semiconductor layers with different thicknesses respectively, and V1 and V2 are the pulse voltages applied to the two semiconductor layers. Therefore, by obtaining the transient electroluminescence time of the two organic semiconductor layers with different thicknesses, the carrier mobility of the organic semiconductor to be tested can be obtained according to formula (2).

[0035] Specifically, the method for measuring the mobility of organic semiconductors based on transient electroluminescence includes the following steps:

[0036] Step S1. Prepare two organic electroluminescent devices. Both organic electroluminescent devices include an organic semiconductor layer to be tested. The thicknesses of the organic semiconductor layers in the two organic electroluminescent devices are set as d1 and d2, respectively, and d1 is not equal to d2. Except for the difference in the thickness of the organic semiconductor layer to be tested, the other organic layers and electrode structures of the two organic electroluminescent devices are the same.

[0037] Step S2. Based on the driving voltages V1 and V2 of the two organic electroluminescent devices under the same current density, positive rectangular pulse voltage signals with high levels of V1 and V2 and low levels of zero are applied to the two organic electroluminescent devices. The transient electroluminescence time τ of the organic electroluminescent devices with thicknesses of d1 and d2 is measured using a transient spectrometer. d1 and τ d2The transient electroluminescence time is defined as the time corresponding to the rising edge of the transient electroluminescence signal reaching 10% intensity.

[0038] Step S3. According to τ d1 and τ d2 The transient electroluminescence time difference Δτ of organic electroluminescent devices with different thicknesses was calculated. d =|(τ d1 -τ d2 According to the organic semiconductor mobility calculation formula μ=|(d1-d2)| 2 / [Δτ d ·Calculate the mobility of the organic semiconductor material under test using |(V1-V2)|];

[0039] Step S4. According to the measurement steps S1-S3, measure the mobility of the organic semiconductor under test under different current densities, and the mobility under different electric field strengths E=|(V1-V2) / (d1-d2)| can be obtained.

[0040] Therefore, the aforementioned testing method utilizes the fact that the thickness difference of the organic semiconductor layer in the organic electroluminescent device causes different transient electroluminescence times, thereby forming a transient electroluminescence time difference (Δτ). d This time difference is due to the migration time of charge carriers in the organic semiconductor material with the thickness difference. Therefore, this time difference Δτ can be considered as... d It is the transient electron emission time when the charge carrier migrates in an organic semiconductor film with a thickness of |d1-d2| when the applied voltage is |V1-V2|. Therefore, the carrier mobility of the organic semiconductor film at this current density can be calculated according to formula (2).

[0041] Therefore, compared with the traditional transient electroluminescence method, the proposed method for measuring the mobility of organic semiconductors based on transient electroluminescence is not limited by the prerequisite of measuring minority carrier mobility. Even though the hole mobility of organic semiconductor materials is generally higher than that of electron mobility, this method can still measure the hole mobility of organic semiconductors, thus solving the problem that the traditional transient electroluminescence method is difficult to accurately measure hole mobility. Furthermore, this method does not require the preparation of micron-sized thin film samples, requiring less sample than the time-of-flight method, thus maintaining the advantage of transient electroluminescence in measuring mobility. In addition, since the transient electroluminescence time difference is obtained by using the thickness difference of the organic semiconductor thin film, the transient electroluminescence time error caused by the interface barrier can be effectively eliminated, thereby overcoming the influence of the interface barrier between the organic semiconductor layer and the electrode, and between organic semiconductor layers, on the accuracy of mobility, resulting in a more accurate carrier mobility.

[0042] The aforementioned method for measuring the mobility of organic semiconductors based on transient electroluminescence, wherein the organic electroluminescent device sequentially comprises: an anode, a hole injection layer, a hole transport layer, an electron blocking layer, an emissive layer, a hole blocking layer, an electron transport layer, an electron injection layer, and a cathode. This organic electroluminescent device, by placing an electron blocking layer between the hole transport layer and the emissive layer, and a hole blocking layer between the electron transport layer and the emissive layer, and by placing an electron blocking layer between the electron transport layer and the emissive layer respectively, effectively blocks electrons and holes from crossing the emissive layer into the transport layer. This confines the recombination region of the device within the emissive layer, stabilizing the recombination region and thus reducing the error in the transient electroluminescence time difference.

[0043] The aforementioned organic electroluminescent device can be used to measure both the electron mobility and hole mobility of organic semiconductor materials. When used to measure the electron mobility of organic semiconductor materials, the electron transport layer in the organic electroluminescent device is the organic semiconductor material to be measured; and when used to measure the hole mobility of organic semiconductor materials, the hole transport layer in the organic electroluminescent device is the organic semiconductor material to be measured.

[0044] During electron mobility or hole mobility testing, the holes and electrons recombine in the emissive layer to emit light. Therefore, the thickness of the emissive layer affects the distribution of the recombination region, thereby influencing the transient electroluminescence time. In a preferred embodiment, by setting the thickness of the emissive layer to 1–10 nm, the thickness of the emissive layer is significantly lower than the thickness difference of the organic semiconductor layer under test, thereby reducing the transient electroluminescence time error caused by changes in the recombination region position and improving the accuracy of mobility testing.

[0045] Besides the thickness of the light-emitting layer potentially causing mobility errors, the thickness difference of the organic semiconductor under test also affects the accuracy of the mobility. This is because a smaller thickness difference in the organic semiconductor layer under test within an organic electroluminescent device will increase the transient electroluminescence time difference Δτ. d It also decreases when Δτ d When the time resolution is reduced to near that of the transient electroluminescence signal, then Δτ dThe measurement error will increase rapidly, leading to an increase in the mobility error. On the other hand, while a thicker organic semiconductor layer can reduce the error, it also leads to material waste. Therefore, in a preferred embodiment, the thickness of the organic semiconductor layer to be measured is 50–300 nm, and the difference between d1 and d2 is 50–200 nm, resulting in a smaller error and less waste. That is, when measuring electron mobility, the thickness of the electron transport layer is 50–300 nm, and the difference between the thicknesses d1 and d2 of the two electron transport layers in the two organic electroluminescent devices is 50–200 nm; when measuring hole mobility, the thickness of the hole transport layer is 50–300 nm, and the difference between the thicknesses d1 and d2 of the two hole transport layers in the two organic electroluminescent devices is 50–200 nm.

[0046] Furthermore, when measuring electron or hole mobility, the thickness of the opposing hole transport layer or electron transport layer also needs to be optimized to achieve a more balanced carrier state in the device. For example, when measuring the electron mobility of the electron transport layer, the thickness of the hole transport layer also needs to be optimized. When the electron transport layer thickness is 50–300 nm, a hole transport layer thickness of 50–150 nm will provide a more suitable transient electroluminescence time. Conversely, when measuring the hole mobility of the hole transport layer, the thickness of the electron transport layer needs to be optimized. For instance, when the hole transport layer thickness is 50–300 nm, an electron transport layer thickness of 30–100 nm is better and will have a smaller impact on the transient electroluminescence time.

[0047] Furthermore, to better obtain the transient electroluminescence time, appropriate pulse width and frequency need to be set. Typically, the pulse width is determined by the response time of the device from the rise of the transient electroluminescence signal to a stable state. If the device responds quickly, a smaller pulse width can be set, and vice versa. The frequency setting is also determined by the pulse width; a larger pulse width requires a lower data acquisition frequency, and vice versa. A higher data acquisition frequency results in more timely and accurate collection of the transient electroluminescence signal. Therefore, in a preferred embodiment, depending on the thickness of the organic semiconductor under test, in step S2, the high-level pulse width of the pulse voltage signal is 10 μs to 1000 μs, which can fully cover the response range of transient electroluminescence, and the frequency is set to 10 to 10... 5 Hz, which can quickly and accurately collect transient EL signals and reduce test errors.

[0048] Furthermore, in step S2, the rise time of the pulse voltage signal applied to the organic electroluminescent device also affects the accuracy of the transient electroluminescence time. Experiments have shown that when the rise time of the applied pulse voltage signal is too long, the device response time becomes longer than the rise time of the pulse voltage signal. In this case, the transient electroluminescence time difference, which reflects the thickness difference, cannot be measured. Therefore, in a preferred embodiment, in step S2, the rise time of the pulse voltage signal applied to the organic electroluminescent device is controlled to be ≤50ns to avoid the device response time exceeding the rise time of the pulse voltage signal, ensuring that the obtained transient electroluminescence time difference accurately reflects the thickness difference of the organic semiconductor material.

[0049] In summary, the method for measuring the mobility of organic semiconductors based on transient electroluminescence described in this invention utilizes the thickness difference of the organic semiconductor thin film in the organic electroluminescence device to obtain the transient electroluminescence time difference (Δτ). d The method can be used to calculate the mobility information, and has the characteristics of small error, few restrictions on the sample to be tested, and the ability to measure electron mobility and hole mobility. It can be widely used for the testing of carrier mobility in organic semiconductor materials.

[0050] It should be noted that the method for measuring the mobility of organic semiconductors based on transient electroluminescence in this invention uses a transient spectrometer for measurement, such as... Figure 1 As shown, the main structural components of the transient spectrometer include: a signal generator 101, an organic electroluminescent device sample 102, a spectrometer 103, a photodetector 104, and an industrial control system 105.

[0051] To further illustrate the method for measuring the mobility of organic semiconductors based on transient electroluminescence provided by the present invention, the following embodiments are provided.

[0052] Example 1

[0053] The electron mobility of the electron transport material ET2 was tested using a method based on transient electroluminescence to measure the mobility of organic semiconductors.

[0054] An electron transport layer for an organic electroluminescent device was prepared using ET2, an electron transport material. The specific results of the organic electroluminescent device are as follows: Figure 2 As shown, it sequentially includes: an anode 201; a hole injection layer 202 with a thickness of 10 nm; a hole transport layer 203 with a thickness of 50 nm; an electron blocking layer 204 with a thickness of 10 nm; a light-emitting layer 205 with a thickness of 5 nm; a hole blocking layer 206 with a thickness of 10 nm; an electron transport layer 207 with thicknesses d1 and d2 of 50 nm and 150 nm, respectively; an electron injection layer 208 with a thickness of 10 nm; and a cathode 209 with a thickness of 100 nm.

[0055] In this system, an organic electroluminescent device sample 102 with the mobility to be measured is placed in the sample chamber of a spectrometer 103. A signal generator 101 provides a pulsed voltage signal applied to the organic electroluminescent device sample 102. This pulsed voltage signal is synchronously connected to the spectrometer 103, ensuring that the pulsed voltage signal and the detected transient electroluminescence characteristics are synchronized. The emission signal of the organic electroluminescent device sample 102 is detected by the photodetector 104 of the spectrometer 103, and the transient electroluminescence characteristics of the device sample are displayed on the industrial control system 105.

[0056] During testing, pulsed voltage signals were applied across the electrodes of the organic electroluminescent device under test. The corresponding pulse voltages were for current densities of 0.05, 0.1, 0.2, and 0.5 mA / cm². 2 The corresponding voltage values ​​are as follows: For an organic electroluminescent device with a thickness of d1, the voltages are 2.316V, 2.355V, 2.409V, and 2.519V; for an organic electroluminescent device with a thickness of d2, the voltages are 2.639V, 2.831V, 3.079V, and 3.518V. To allow the transient electroluminescence signal of the organic electroluminescent device to rise to a stable state, a current density of 0.05mA / cm² is required. 2 The pulse voltage signal has a pulse width of 700 μs; for current densities of 0.1, 0.2, and 0.5 mA / cm². 2 The pulse voltage signal has a pulse width of 350μs. Figure 3 The transient electroluminescence characteristics of the organic electroluminescent device described in Embodiment 1 of this application (Figure a shows d1 = 50 nm, Figure b shows d2 = 150 nm) under different current densities.

[0057] Based on formula (2) and formula E=|(V1-V2) / (d1-d2)|, the mobility under different electric field intensities is calculated as shown in Table 1 below.

[0058] Table 1

[0059]

[0060] Example 2

[0061] The electron mobility of the electron transport material blend ET2:silver (silver doped at 5% by mass) was tested.

[0062] An organic electroluminescent device for measuring mobility was prepared. The structure of this organic electroluminescent device was basically the same as that in Example 1, except that: the electron transport layer was an electron transport material blend ET2:silver, wherein the thicknesses d1 and d2 of the electron transport layer 207 were 100 nm and 300 nm respectively, the hole transport layer 203 had a thickness of 100 nm, and the remaining functional layers were the same as in Example 1.

[0063] A pulsed voltage signal was applied across the electrodes of the organic electroluminescent device described in Example 2. The corresponding pulsed voltages were the device's current densities at 2, 5, 10, 20, and 50 mA / cm². 2 The corresponding voltage values ​​are as follows: For an organic electroluminescent device with a thickness of d1, the voltages are 2.614V, 2.850V, 3.154V, 3.613V, and 4.508V; for an organic electroluminescent device with a thickness of d2, the voltages are 2.736V, 3.142V, 3.708V, 4.602V, and 6.360V. To allow the transient electroluminescence signal of the organic electroluminescent device to rise to a stable state, the pulse width is set to 70μs, and the transient electroluminescence characteristics of the organic electroluminescent device under different current densities are measured.

[0064] Based on formula (2) and formula E=|(V1-V2) / (d1-d2)|, the mobility under different electric field intensities is calculated as shown in Table 2.

[0065] Table 2

[0066]

[0067] Example 3

[0068] The hole mobility of the HT3 transport material was tested.

[0069] An organic electroluminescent device for measuring mobility was fabricated. The structure of this organic electroluminescent device is basically the same as that in Example 1, except that the thicknesses d1 and d2 of the hole transport layer 203 are 100 nm and 300 nm, respectively, and the thickness of the electron transport layer 207 is 50 nm. The remaining functional layers are the same as in Example 1.

[0070] A pulsed voltage signal was applied across the electrodes of the organic electroluminescent device described in Example 3. The corresponding pulsed voltages were the device's current densities at 2, 5, 10, 20, and 50 mA / cm². 2 The corresponding voltage values ​​are as follows: For an organic electroluminescent device with a thickness of d1, the voltages are 2.684V, 2.823V, 2.980V, 3.208V, and 3.680V; for an organic electroluminescent device with a thickness of d2, the voltages are 3.023V, 3.432V, 3.887V, 4.528V, and 5.783V. To allow the emission signal of the organic electroluminescent device to rise to a stable state, the pulse width is set to 75μs, and the transient electroluminescence characteristics of the organic electroluminescent device under different current densities are measured.

[0071] Based on formulas (2) and (3), E = |(V1-V2) / (d1-d2)|, the mobility under different electric field intensities is calculated as shown in Table 3.

[0072] Table 3

[0073]

[0074] Comparative Example 1

[0075] The electron mobility of the electron transport material ET2 was tested using the time-of-flight method. An ET2 thin film with a thickness of 5 μm was deposited by vapor deposition, and the mobility values ​​under different electric field strengths are shown in Table 4 below.

[0076] Table 4

[0077]

[0078] Comparing the electron mobilities obtained from Examples 1 and Comparative Example 1 in Tables 1 and 4, it can be seen that the electron mobilities measured by this method are similar to those measured by the time-of-flight method, indicating that the mobility measured by this method has high accuracy. Furthermore, compared to the time-of-flight method, it eliminates the need to prepare micron-thickness films, significantly reducing the amount of material samples used. On the other hand, as shown in Examples 1-3, this method, based on transient electroluminescence, can accurately measure electron mobility, overcoming the shortcomings of traditional transient electroluminescence methods in accurately measuring electron mobility.

[0079] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; or they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention based on the specific circumstances.

[0080] It is understood that those skilled in the art can make equivalent substitutions or modifications to the technical solution and inventive concept of the present invention, and all such substitutions or modifications should fall within the protection scope of the appended claims.

Claims

1. A method for measuring the mobility of organic semiconductors based on transient electroluminescence, characterized in that, The method includes the following steps: Step S1. Prepare two organic electroluminescent devices. Both organic electroluminescent devices include an organic semiconductor layer to be tested. The thicknesses of the organic semiconductor layers in the two organic electroluminescent devices are set as d1 and d2, respectively, and d1 is not equal to d2. Except for the difference in the thickness of the organic semiconductor layer to be tested, the other organic layers and electrode structures of the two organic electroluminescent devices are the same. Step S2. Based on the driving voltages V1 and V2 of the two organic electroluminescent devices under the same current density, positive rectangular pulse voltage signals with high levels of V1 and V2 and low levels of zero are applied to the two organic electroluminescent devices. The transient electroluminescence time τ of the organic electroluminescent devices with thicknesses of d1 and d2 is measured using a transient spectrometer. d1 and τ d2 The transient electroluminescence time is defined as the time corresponding to the rising edge of the transient electroluminescence signal reaching 10% intensity. Step S3. According to τ d1 and τ d2 The transient electroluminescence time difference Δτ of organic electroluminescent devices with different thicknesses was calculated. d =|(τ d1 -τ d2 According to the organic semiconductor mobility calculation formula μ=|(d1-d2)| 2 / [Δτ d ·Calculate the mobility of the organic semiconductor material under test using |(V1-V2)|]; Step S4. According to the measurement steps S1-S3, measure the mobility of the organic semiconductor under test under different current densities, and the mobility under different electric field strengths E=|(V1-V2) / (d1-d2)| can be obtained.

2. The method for measuring the mobility of organic semiconductors based on transient electroluminescence according to claim 1, characterized in that, The organic electroluminescent device comprises, in sequence: an anode, a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer, and a cathode, wherein the electron transport layer or the hole transport layer is the organic semiconductor layer to be tested.

3. The method for measuring the mobility of organic semiconductors based on transient electroluminescence according to claim 2, characterized in that, The thickness of the light-emitting layer is 1–10 nm.

4. The method for measuring the mobility of organic semiconductors based on transient electroluminescence according to claim 2, characterized in that, The thickness of the organic semiconductor layer to be tested is 50–300 nm, and the difference between d1 and d2 is 50–200 nm.

5. The method for measuring the mobility of organic semiconductors based on transient electroluminescence according to claim 4, characterized in that, When the electron transport layer is the organic semiconductor layer to be tested, the hole transport layer thickness is 50–150 nm.

6. The method for measuring the mobility of organic semiconductors based on transient electroluminescence according to claim 4, characterized in that, When the hole transport layer is the organic semiconductor layer to be tested, the thickness of the electron transport layer is 30-100 nm.

7. The method for measuring the mobility of organic semiconductors based on transient electroluminescence according to claim 1, characterized in that, In step S2, the high-level pulse width of the pulse voltage signal is 10–1000 μs, and the frequency is 10–10. 5 Hz.

8. The method for measuring the mobility of organic semiconductors based on transient electroluminescence according to claim 7, characterized in that, In step S2, the rise time of the pulse voltage signal applied to the organic electroluminescent device is ≤50ns.

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