Organic semiconductor mobility testing method

Abstract

The invention discloses a method for testing the mobility of an organic semiconductor, which relates to the technical field of optoelectronic device testing, and is characterized in that the carrier mobility is obtained by utilizing the difference of transient electroluminescence time caused by the thickness difference of organic semiconductor layers made of the same material. According to the method, by adjusting the thickness ratio of the electron blocking layer to the hole blocking layer, the carrier with the mobility to be measured enters the light-emitting layer later than the carrier of another kind, so that the transient electroluminescence time of the carrier with the mobility to be measured passing through the thickness difference part of the organic semiconductor film is accurately recorded, and the testing accuracy is improved. As the method is not limited by preconditions for measuring minority carrier mobility, the method can be suitable for measuring electron or hole mobility, and the defect that the hole mobility is difficult to accurately measure by a traditional transient electroluminescence method is overcome.

Description

Technical Field

[0001] The invention relates to the technical field of optoelectronic device testing, and in particular to an organic semiconductor mobility testing method. Background Art

[0002] OLED is essentially a device based on DC drive. Its principle is that when voltage is applied to the positive and negative electrodes, electrons and holes move from the cathode and anode to the light-emitting layer respectively, combine in the light-emitting layer to form excitons, and the excitons release energy after de-excitation, which is manifested as light radiation, that is, the luminescence process. Through research, it is found that the injection and transmission ability of carriers in OLED devices is a crucial factor affecting the performance of the device. The main parameter for measuring the carrier transmission ability is the carrier mobility μ, which directly reflects the mobility of carriers under the electric field. Since there are inevitably some defects and non-radiative recombination centers inside the OLED device, the carrier transport and recombination process will inevitably be affected. Therefore, measuring the carrier transport of the organic functional layer in the OLED plays a vital role in judging the optoelectronic performance of the OLED device.

[0003] There are many existing methods for measuring the carrier mobility of organic semiconductor materials. For example, the Chinese patent application with publication number CN117377365A discloses a method for measuring the mobility of organic semiconductors based on transient electroluminescence. This method uses the thickness difference of the organic semiconductor film to be measured to generate the corresponding transient electroluminescence time difference, and then according to μ=|(d 1 -d 2 )| 2 / [Δτd·|(V 1 -V 2)|] The carrier mobility of the organic semiconductor film can be calculated. The transient electroluminescence method uses a pulse voltage signal to excite a transient luminescence signal, and the carrier mobility can be calculated by detecting the transient electroluminescence time. However, since the hole mobility of organic semiconductor materials is generally higher than the electron mobility, when the hole mobility is tested using the existing transient electroluminescence method, the thickness matching between the device's electron blocking layer and the hole blocking layer is relatively small, and the electron transport layer's electron transport is relatively slow, which may cause the hole migration to be too fast and the electron migration to be too slow, so that the holes and electrons do not have time to recombine in the luminescent area. The thickness difference of the materials to be tested is not enough to obtain the luminescence signal difference of the device in the measurement, so the transient luminescence signal cannot be collected for mobility calculation. Similarly, if the hole injection and transport of the hole transport layer are slow and the thickness of the hole blocking layer and the electron transport layer are inappropriate when testing the electron mobility of organic semiconductor materials, the electrons will migrate too fast and the holes will migrate too slowly, causing the recombination area to shift, making it impossible to accurately collect the transient electroluminescence time of the part with a thickness difference in the organic semiconductor film, resulting in difficulty in ensuring the accuracy of the measurement results. The measurement of electron and hole mobilities is greatly restricted, resulting in mobility errors.

[0004] It can be seen that the existing technology still needs to be improved and enhanced. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a method for testing the mobility of an organic semiconductor, aiming to improve the accuracy of testing the mobility of an organic semiconductor based on a transient electroluminescence method.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for testing the mobility of an organic semiconductor comprises the following steps:

[0008] Step S1, preparing two organic electroluminescent devices, wherein the two organic electroluminescent devices respectively contain an organic semiconductor material to be tested with different thicknesses;

[0009] Step S2, using a digital multimeter to measure the driving voltage of the two organic electroluminescent devices at the same current density;

[0010] Step S3, using a transient spectrometer to measure the transient electroluminescence time of the two organic electroluminescent devices at different driving voltages;

[0011] Step S4, calculating the mobility of the organic semiconductor material to be tested according to its thickness, driving voltage and transient electroluminescence time;

[0012] Step S5, repeating the measurement steps S1-S4 to measure the mobility of the organic semiconductor under different current densities to obtain the mobility under different electric field strengths E;

[0013] Wherein, in the step S1, the two organic electroluminescent devices both include an anode, a cathode, 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; when the hole mobility of the organic semiconductor material is tested, the hole transport layers of the two organic electroluminescent devices are prepared from the organic semiconductor material with the mobility to be tested, and the ratio of the thickness of the electron blocking layer to the hole blocking layer is ≥10; when the electron mobility of the organic semiconductor material is tested, the electron transport layers of the two organic electroluminescent devices are prepared from the organic semiconductor material with the mobility to be tested, and the ratio of the thickness of the hole blocking layer to the electron blocking layer is ≥5.

[0014] Beneficial effects:

[0015] The present invention provides a method for testing the mobility of an organic semiconductor, which is a method based on a transient electroluminescence method. On the basis of the transient electroluminescence method, the method uses the difference in thickness of an organic semiconductor layer of the same material to cause a difference in transient electroluminescence time, and then calculates the carrier mobility of the organic semiconductor layer; in order to improve the accuracy of the test, the method adjusts the relationship between the ratio of the thickness of the electron blocking layer / hole blocking layer so that the carrier of the mobility to be tested enters the light-emitting layer later than another carrier, thereby accurately recording the transient electroluminescence time of the carrier of the mobility to be tested through the thickness difference portion of the organic semiconductor film, thereby improving the accuracy of the test result. Compared with the prior art, the present method does not need to be limited by the prerequisite for measuring minority carrier mobility, and can be applied to the measurement of electron or hole mobility, solving the problem that the traditional transient electroluminescence method is difficult to accurately measure hole mobility. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the testing principle of measuring mobility using the transient electroluminescence method of the present invention.

[0017] Figure 2 Schematic diagram of the structure of an organic electroluminescent device.

[0018] Figure 3 Schematic diagram of the structure of single electron device tested by SCLC method.

[0019] Figure 4 The mobilities under different electric field strengths measured in Examples 1, 2 and 3 are shown.

[0020] Figure 5 The mobility under different electric field strengths was measured by impedance spectroscopy for comparative example 3.

[0021] Markings in the accompanying drawings: 101, signal generator; 102, organic electroluminescent device sample whose mobility is to be measured; 103, spectrometer; 104, photodetector; 105, 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 DESCRIPTION

[0022] The present invention provides a method for testing the mobility of an organic semiconductor. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] See also Figure 1 The present invention provides a method for testing the mobility of an organic semiconductor, which specifically comprises the following steps:

[0024] Step S1, preparing two organic electroluminescent devices, namely device A and device B, wherein the structures of device A and device B both include an anode, a cathode, and a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, a hole blocking layer, an electron transport layer and an electron injection layer sequentially arranged between the anode and the cathode (the hole injection layer, the hole transport layer, the electron blocking layer, the light-emitting layer, the hole blocking layer, the electron transport layer and the electron injection layer are all organic functional layers); when device A and device B are used to test the hole mobility of an organic semiconductor material, the hole transport layers of device A and device B are both prepared from the organic semiconductor material to be tested, and the thickness d of the hole transport layer in device A is 1 Not equal to the thickness d of the hole transport layer in device B 2 , but the other functional layers in device A and device B are the same, and at the same time, in device A and device B, the ratio of the thickness of the electron blocking layer to the hole blocking layer is ≥10; when device A and device B are used to measure the electron mobility of organic semiconductor materials, the electron transport layers of device A and device B are prepared from the organic semiconductor material to be measured, and the thickness of the electron transport layer in device A is d 1 Not equal to the thickness d of the electron transport layer in device B 2 , but the other organic functional layers of device A and device B are the same, and at the same time, the thickness ratio of the hole blocking layer to the electron blocking layer is ≥5;

[0025] Step S2: Use a digital multimeter to measure the driving voltage of device A and device B at the same current density, and obtain the driving voltages of device A and device B as V and V, respectively. 1 and V 2 ;

[0026] Step S3, using a transient spectrometer to measure the transient electroluminescence time of the two organic electroluminescent devices at different driving voltages, specifically: when device A and device B are loaded with high levels of V 1 and V 2 , a positive rectangular pulse voltage signal with a low level of zero, and measured by a transient spectrometer, the transient electroluminescence time of device A and device B are τ d1 and τ d2 , the transient electroluminescence time is defined as the corresponding time when the transient electroluminescence signal rises to 10% intensity;

[0027] Step S4, calculating the mobility of the organic semiconductor material to be tested according to its thickness, driving voltage and transient electroluminescence time, specifically: d1 and τ d2 The transient electroluminescence time difference Δτ between device A and device B is calculated d =|(τ d1 -τ d2 )|, according to the organic semiconductor mobility calculation formula μ=|(d 1 -d 2 )| 2 / [Δτ d ·|(V 1 -V 2 )|] calculate the mobility of the organic semiconductor material to be tested;

[0028] Step S5, repeat the measurement steps S1-S4 to measure the mobility of the organic semiconductor to be measured at different current densities, and obtain different electric field strengths E=|(V 1 -V 2 ) / (d 1 -d 2 )|under the mobility.

[0029] The above-mentioned organic semiconductor mobility test method is a test method based on the transient electroluminescence method. On the basis of the transient electroluminescence method, the difference in thickness of the organic semiconductor layer of the same material will lead to different transient electroluminescence times, and then the carrier mobility of the organic semiconductor layer is calculated. The specific calculation principle is: based on the same current density, the mobility of two organic semiconductor layers of the same material and different thicknesses is the same, so the organic semiconductor mobility formula (1) can be obtained:

[0030] μ=d 2 / (v·t d )=|(d 1 -d 2 )| 2 / [Δτ d ·|(V 1 -V 2)|] (1)

[0031] In formula (1), Δτ d is the transient electroluminescence time difference of two organic semiconductor layers with different thicknesses, which can be obtained by measuring the transient electroluminescence time of two organic semiconductor layers with different thicknesses respectively, d 1 and d 2 are the thicknesses of two organic semiconductor layers with different thicknesses, V 1 and V 2 is the voltage applied to the two electrodes of the organic electroluminescent device. Therefore, by obtaining the transient electroluminescence time of two organic semiconductor layers with different thicknesses, the carrier mobility of the organic semiconductor to be measured can be obtained according to formula (1). It should be noted that the organic semiconductor layer can be an electron transport layer (when measuring electron mobility) or a hole transport layer (when measuring hole mobility).

[0032] In order to obtain the transient electroluminescence time difference of the carrier passing through the difference part of the organic semiconductor layer to be measured, the method adjusts the relationship between the electron blocking layer / hole blocking layer thickness ratio so that the carrier of the mobility to be measured enters the light-emitting layer later than another carrier, thereby accurately recording the transient electroluminescence time of the carrier of the mobility to be measured passing through the difference part of the thickness of the organic semiconductor film. Specifically, when measuring the hole mobility of the organic material, the method makes the thickness of the electron blocking layer much greater than the thickness of the hole blocking layer to extend the time required for the hole to pass through the electron blocking layer so that the electrons can reach the light-emitting layer first, and the thickness difference of the organic material to be measured is used to accurately obtain the electroluminescence time difference of the material to be measured; and when measuring the electron mobility of the organic material, the method makes the thickness of the hole blocking layer much greater than the thickness of the electron blocking layer to extend the time required for the electron to pass through the hole blocking layer so that the holes can reach the light-emitting layer first, and the thickness difference of the organic material to be measured is used to accurately obtain the electroluminescence time difference of the material to be measured.

[0033] Compared with the existing technology, this method is not limited by the prerequisites for measuring minority carrier mobility and can be applied to the measurement of electron or hole mobility, which solves the problem that the traditional transient electroluminescence method is difficult to accurately measure hole mobility and cannot test accurate results. In addition, compared with the time-of-flight method, the thickness of the organic functional layer to be measured in this method is only at the level of hundreds of nanometers, which saves sample consumption, reduces the pressure of organic material synthesis, and maintains the advantage of transient electroluminescence in measuring mobility.

[0034] However, under the premise that the carrier with the mobility to be measured enters the light-emitting layer later than the other carrier, the greater the ratio of the blocking layer thickness, the greater the material loss. In this regard, in a preferred embodiment, when measuring the hole mobility of the organic semiconductor material, the ratio of the thickness of the electron blocking layer to the hole blocking layer is 10-50, and an accurate electroluminescence time can be obtained with less material loss. When measuring the electron mobility of the organic semiconductor material, the ratio of the thickness of the hole blocking layer to the electron blocking layer is 5-50, which has a suitable electroluminescence time and less material loss.

[0035] In addition, the transient electroluminescence time τ of device A and device B d1 and τ d2 When the difference is large, the transient luminescence time difference can be accurately obtained by measuring the transient luminescence time of device A and device B. The electroluminescence time is related to the thickness of the organic semiconductor material, especially the thickness difference between device A and device B. In order to make the mobility test more accurate, in a preferred embodiment, in step S1, the thickness of the organic semiconductor material to be tested in device A and device B (when measuring hole mobility, the organic semiconductor layer is a hole transport layer, and when measuring electron mobility, the organic semiconductor layer is a hole transport layer) is 50-350nm, and the thickness difference between the organic semiconductor material to be tested in device A and device B is 50-300nm.

[0036] As a further optimization, it is also necessary to control the composition of the hole transport layer or electron transport layer opposite to the organic semiconductor material to be measured, as well as the thickness of the electron blocking layer and the hole blocking layer, so that the carriers of the device fall in the luminescent area as much as possible. In a preferred embodiment, when measuring the electron mobility of the organic semiconductor material, the thickness of the hole blocking layer is 50 to 200 nm, the thickness of the electron blocking layer is 5 to 30 nm, and the thickness of the hole transport layer is 30 to 150 nm, which has a more suitable transient electroluminescence time. When measuring the hole mobility of the organic semiconductor material, the preferred thickness of the electron blocking layer is 50 to 300 nm, the preferred thickness of the hole blocking layer is 5 to 30 nm, and the preferred thickness of the electron transport layer is 15 to 100 nm, and a more accurate electroluminescence time can be obtained.

[0037] In addition, in step S1 of the aforementioned test method, when measuring the hole mobility of the organic semiconductor material, the electrons are preferably allowed to reach the light-emitting layer first. To this end, in addition to adjusting the thickness of the electron blocking layer and the hole blocking layer, the electrons are also required to have a faster rate in the electron transport layer. In this regard, in a preferred embodiment, the electron transport layer is prepared from an n-doped electron transport composition, and n-doping is used to increase the electron transport rate in the electron transport layer to ensure that the electrons reach the light-emitting layer first.

[0038] Similarly, when measuring the electron mobility of organic semiconductor materials, it is necessary to allow holes to reach the light-emitting layer first. Therefore, in addition to changing the thickness ratio of the hole blocking layer to the electron blocking layer, in a preferred embodiment, the hole transport layer is prepared from a p-doped hole transport composition, wherein p-doping can increase the transport rate of holes in the hole transport layer so that holes can reach the light-emitting layer first.

[0039] Specifically, the n-doped electron transport composition includes an n-type dopant and an electron transport material, wherein the n-type dopant is selected from one or a combination of Li, Na, K, Rb, Cs, Yb, Ag, Mg, Zn, Ta, and Pt, and these dopants can increase the electron transport rate; the electron transport material includes one of the structural formulas ET-1 to ET-40:

[0040]

[0041]

[0042]

[0043]

[0044]

[0045] As a more preferred embodiment, the doping mass ratio of the n-dopant in the n-doped electron transport composition is 0.5% to 10%, and the thickness of the electron transport layer is 15 to 100 nm, which has a faster electron transport rate and can ensure that electrons reach the light-emitting layer first.

[0046] Specifically, the p-doped hole transport composition consists of a p-type dopant and a hole transport material, wherein the p-type dopant is selected from WO 3 、V 2 O 5 、MoO 2 、Co 3 O 4 And the structural formula is one or a combination of HI-1 to HI-17:

[0047]

[0048]

[0049] The hole transport material is selected from one of the structural formulas HT-1 to HT-22:

[0050]

[0051]

[0052]

[0053] The hole transport layer prepared by using the aforementioned p-type dopant and hole transport material has a faster hole transport rate, which can ensure that the holes reach the light-emitting layer first when testing the electron mobility of the organic semiconductor, so as to obtain an accurate electroluminescence time.

[0054] Preferably, the doping mass ratio of the aforementioned p-dopant in the p-doped hole transport composition is 0.5% to 10%, and the thickness of the hole transport layer is 30 to 150 nm, which has a faster hole transport rate.

[0055] In addition, in order to better obtain the transient electroluminescence time, it is necessary to set a suitable pulse width and frequency. In a preferred embodiment, according to the thickness of the organic semiconductor to be measured, 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.

[0056] In summary, the optimized transient electroluminescence method of the present invention measures the mobility of organic semiconductors by utilizing the thickness difference of the organic semiconductor film in the organic electroluminescent device and adjusting the thickness ratio of the hole blocking layer to the electron blocking layer to obtain an accurate transient electroluminescence time difference (Δτ d ), and then calculate its mobility information. It has the characteristics of small error, few restrictions on the sample to be tested, and can measure electron mobility and hole mobility. It can be widely used in the test of carrier mobility of organic semiconductor materials.

[0057] It should be noted that the method for optimizing the transient electroluminescence method for measuring the mobility of organic semiconductors described in the present 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 a control system 105.

[0058] To further illustrate the method for testing the mobility of an organic semiconductor provided by the present invention, the following examples are provided.

[0059] Example 1

[0060] The hole mobility of the hole transport material HT-1 was tested using the organic semiconductor mobility test method:

[0061] The hole transport layer of the organic electroluminescent device A and the device B are prepared with the hole transport material HT-1. The specific structures of the device A and the device B are as follows: Figure 2 As shown, it includes an anode 201; a hole injection layer 202 with a thickness of 10 nm; a hole transport layer 203. The thickness of the hole transport layer 203 in device A and device B is d 1 and d 2 The thickness of the electron blocking layer 204 is 100nm and 300nm respectively; the thickness of the electron blocking layer 204 is 100nm; the thickness of the light-emitting layer 205 is 5nm; the thickness of the hole blocking layer 206 is 10nm; the thickness of the electron transport layer 207 is 30nm, and the electron transport layer is prepared by a blend of ET-8 and Ag (wherein Ag is doped at a mass ratio of 1%); the thickness of the electron injection layer 208 is 1nm; and the thickness of the cathode 209 is 100nm.

[0062] The device A and device B samples 102 are placed in the sample compartment of the spectrometer 103. The signal generator 101 provides a pulse voltage signal applied to the device A and device B samples 102. The pulse voltage signal is synchronously connected to the spectrometer 103, so that the pulse voltage signal and the detected transient electroluminescence characteristics are synchronized. The luminescence signals of the device A and device B samples 102 are detected by the photodetector 104 of the spectrometer 103, and the transient electroluminescence characteristics of the device samples are presented on the industrial control system 105.

[0063] During the test, a pulse voltage signal is applied to both ends of the electrodes of device A and device B. The corresponding pulse voltages are 2, 5, 10, 20, and 50 mA / cm 2 The corresponding voltage value. 1 The voltages of device A with a thickness of d are 2.637V, 2.826V, 3.207V, 3.629V, and 4.212V respectively; 2 The voltages of device B with a thickness of 2.841V, 3.168V, 3.834V, 4.585V, and 5.639V are respectively. In order to make the transient electroluminescent signal of the organic electroluminescent device rise to a stable state, the pulse width is 75μs. The time differences are respectively 2.81×10 -7 s, 5.32×10 -7 s, 8.73×10 -7 s, 1.75×10 - 6 s, 2.76×10 -6 s.

[0064] According to formula (1) and formula E = |(V 1 -V 2 ) / (d 1 -d 2)|, the hole mobility under different electric field strengths is calculated as shown in Table 1 and Figure 4 shown.

[0065] Table 1

[0066]

[0067] Example 2

[0068] The hole mobility of the hole transport material HT-15 was tested using the organic semiconductor mobility test method.

[0069] Organic electroluminescent devices A and B required for measuring mobility were prepared. The structures of device A and device B were basically the same as those in Example 1, except that the hole transport material was HT-15.

[0070] A pulse voltage signal is applied to both ends of the electrodes of device A and device B in Example 2, and the corresponding pulse voltages are respectively 2 The corresponding voltage value. 1 The voltages of device A with a thickness of d are 2.600V, 2.719V, 2.868V, 3.106V and 3.616V respectively; 2 The voltages of device B with different thicknesses are 2.718V, 2.935V, 3.206V, 3.627V and 4.511V respectively. In order to make the luminous signals of device A and device B rise to a stable state, the pulse width is set to 75μs. The time difference is 8.7×10 -8 s, 1.66×10 -7 s, 2.66×10 -7 s, 4.39×10 -7 s, 7.71×10 -7 s. According to formula (1) and formula E = |(V 1 -V 2 ) / (d 1 -d 2 )|, the hole mobility under different electric field strengths is calculated as shown in Table 2 and Figure 4 shown.

[0071] Table 2

[0072]

[0073] Example 3

[0074] The organic semiconductor mobility test method tests the electron mobility of the electron transport material ET-8.

[0075] The organic electroluminescent devices A and B required for measuring mobility were prepared. The structures of the devices A and B were basically the same as those in Example 1, except that the electron transport layer was an electron transport material ET-8, the hole transport layer 203 was a blend of HT-1:HI-16 (HI-16 doped 3% by mass) with a thickness of 50 nm, and the electron transport layer 207 was d 1 and d 2 The thickness of the electron blocking layer 204 is 10 nm; the thickness of the hole blocking layer 206 is 50 nm. The other functional layers are the same as those in Example 1.

[0076] A pulse voltage signal is applied to both ends of the electrodes of device A and device B in Example 3, and the corresponding pulse voltages are respectively 2 The corresponding voltage value. 1 The voltages of device A with a thickness of d are 2.285V, 2.351V, 2.473V, 2.602V and 2.772V respectively; 2 The voltages of device B with different thicknesses are 2.530V, 2.702V, 3.019V, 3.348V and 3.776V respectively. In order to make the transient electroluminescent signals of device A and device B rise to a stable state, the pulse width is set to 75μs. The time differences are 3.04×10 -7 s, 7.26×10 -7 s, 1.437×10 -6 s, 3.206×10 -6 s, 5.831×10 -6 s. According to formula (1) and formula E = |(V 1 -V 2 ) / (d 1 -d 2 )|, the electron mobility under different electric field strengths is calculated as shown in Table 3 and Figure 4 shown.

[0077] Table 3

[0078]

[0079] Comparative Example 1

[0080] The hole mobility of the hole transport material HT-1 was tested.

[0081] An organic electroluminescent device for measuring mobility was prepared. The structure of the organic electroluminescent device was basically the same as that of Example 1, except that the electron blocking layer 204 had a thickness of 10 nm, the hole blocking layer 206 had a thickness of 10 nm, and the other functional layers were the same as those of Example 1.

[0082] The pulse voltage signals are applied to both ends of the electrodes of the organic electroluminescent device described in Comparative Example 1, and the corresponding pulse voltages are respectively 2 The corresponding voltage value. 1 The voltages of organic electroluminescent devices with different thicknesses are 2.673V, 2.865V, 3.227V, 3.748V and 4.356V respectively; 2 The voltages of the organic electroluminescent devices with different thicknesses are 2.887V, 3.235V, 3.878V, 4.707V and 5.738V respectively. In order to make the transient electroluminescent signal of the organic electroluminescent device rise to a stable state, the pulse width is 75μs. The time differences are 1.69×10 -5 s, 1.93×10 -5 s, 1.98×10 -5 s, 1.92×10 -5 s, 2.47×10 -5 s. .

[0083] According to formula (1) and formula E = |(V 1 -V 2 ) / (d 1 -d 2 )|, and the different electric field strengths are calculated as shown in Table 4.

[0084] Table 4

[0085]

[0086] Comparative Example 2

[0087] The electron mobility of the electron transport material ET-8 was tested.

[0088] An organic electroluminescent device for measuring mobility was prepared. The structure of the organic electroluminescent device was basically the same as that of Example 3, except that the electron blocking layer 204 had a thickness of 10 nm, the hole blocking layer 206 had a thickness of 10 nm, and the remaining functional layers were the same as those of Example 3.

[0089] The pulse voltage signals are applied to both ends of the electrodes of the organic electroluminescent device described in Comparative Example 2, and the corresponding pulse voltages are respectively 2 The corresponding voltage value. 1 The voltages of organic electroluminescent devices with a thickness of 2.296V, 2.359V, 2.491V, 2.595V and 2.801V are respectively; for d 2The voltages of the organic electroluminescent devices with different thicknesses are 2.517V, 2.678V, 3.022V, 3.351V and 3.798V respectively. In order to make the transient electroluminescent signal of the organic electroluminescent device rise to a stable state, the pulse width is 75μs. The time differences are 1.76×10 -6 s, 5.73×10 -7 s, -8.70×10 -9 s, -1.70×10 -8 s, -9.70×10 -8 s.

[0090] According to formula (1) and formula E = |(V 1 -V 2 ) / (d 1 -d 2 )|, the electron mobility under different electric field strengths is calculated and shown in Table 5.

[0091] Table 5

[0092]

[0093]

[0094] Comparative Example 3

[0095] Measurement of electron mobility of ET-8 by impedance spectroscopy

[0096] Impedance spectroscopy is a powerful method for studying the dynamic response of carriers and the relaxation process in solid materials. By applying a small amplitude sinusoidal voltage signal to the steady-state SCLC and injecting a small amount of additional alternating carriers, the redistribution process of these carriers leads to an alternating current that lags behind the voltage. By observing the change of impedance or admittance with the signal frequency, the transmission information of carriers in the material can be obtained.

[0097] According to the negative differential susceptance method, there is the following relationship between negative differential admittance -ΔB and capacitance and angular frequency:

[0098] -ΔB=-ω(cc geo ) (2)

[0099] Among them C geo is the geometric capacitance of the device, ω is the angular frequency, and with the relaxation of carriers, a characteristic peak appears in the negative differential susceptance-frequency diagram, with a peak frequency τ r and carrier DC transit time τ dc There is the following relationship between

[0100] Under non-dissipative transport: τ dc =0.56τ r ; (3)

[0101] Under dissipative transport: τ dc = ±0.56τ r (4)

[0102] Here, 0.56 is used as the peak frequency τ r and carrier DC transit time τ dc The conversion coefficient between them is used as the DC transition time τ dc Then, the mobility can be obtained by using formula (5):

[0103]

[0104] V is the voltage applied across the film sample, and L is the film thickness.

[0105] Based on the mobility calculation relationship of the above formula (5), a single electron device for testing the mobility by impedance spectroscopy was prepared to test the electron mobility of ET-8. The device structure is as follows:

[0106] The single electron device DET-8 for measuring the electron mobility of ET-8 has a structure of ITO (95 nm) / ET-8 (300 nm) / 1% Ag:ET (10 nm) / Al (100 nm), and the L value in formula (5) is 300 nm.

[0107] The capacitance-frequency characteristic curves of DET-8 at 4V, 5V, 6V, 7V and 8V were measured, and the corresponding frequencies of its negative differential susceptance-frequency peaks were 46451Hz, 109034Hz, 192578Hz, 295047Hz and 485349Hz, respectively. According to the current-voltage characteristic curve of ET-8, the built-in potential corresponding to the electron injection of the device DET-8 is 1.50V, so the voltages in equation (5) correspond to 2.5V, 3.5V, 4.5V, 5.5V and 6.5V, respectively.

[0108] The electron mobility of ET-8 measured by impedance spectroscopy is calculated according to equations (3) and (5) as shown in Table 6 and Figure 5 As shown. The electron mobility range of material ET-8 is 2.99×10 -5 ~1.20×10 -4 cm 2 / V·s.

[0109] Table 6 Electron mobility of ET-8 at different electric field strengths

[0110]

[0111] Comparative Example 4

[0112] The electron mobility of ET-8 was measured using the SCLC method using the single electron device DET-8 structure. The current density and voltage of the single carrier device in the space charge limited current stage obey the following relationship:

[0113] J = 9 / (8·ε r ·ε 0 ·μ·(U 2 / d 3 )) (6)

[0114] Among them, ε r and ε 0 are the dielectric constant of organic materials and the dielectric constant of vacuum, ε r The value is 2.9, μ is the mobility, U is the voltage drop across the organic material film, and d is the film thickness.

[0115] In the SCLC stage, the mobility under zero electric field strength is 3.25×10 -5 cm 2 / V·s.

[0116] Comparative Example 5

[0117] Measurement of hole mobility of HT-1 by impedance spectroscopy

[0118] Based on the mobility calculation relationship of formula (5) in comparative example 4, a single hole device for testing the mobility by impedance spectroscopy was prepared to test the hole mobility of HT-1. The device structure is as follows:

[0119] The single hole device DHT-1 for measuring the hole mobility of HT-1 has a structure of ITO (95 nm) / HT-1:HI-16 (10 nm) / HT-1 (300) / Al (100 nm), and the L value in formula (5) is 300 nm.

[0120] The capacitance-frequency characteristic curves of DHT-1 at 4V, 5V, 6V, 7V and 8V are measured, and the corresponding frequencies of the negative differential susceptance-frequency peaks are 491431Hz, 1236480Hz, 1928640Hz, 2950826Hz and 5130844Hz respectively. According to the current-voltage characteristic curve of HT-1, the built-in potential corresponding to the hole injection of the device DHT-1 is 1.80V, so the voltages in equation (5) correspond to 2.2V, 3.2V, 4.2V, 5.2V and 6.2V respectively.

[0121] The hole mobility of HT-1 measured by impedance spectroscopy is calculated according to equations (3) and (5) and is shown in Table 7. The hole mobility ranges of HT-1 are 3.59×10 -4 ~1.33×10 -3 cm2 / V·s.

[0122] Table 7 Hole mobility of HT-1 at different electric field strengths

[0123]

[0124]

[0125] Comparison of the hole mobility measured in Example 1 and Comparative Example 5 shows that the hole mobility tested by this method (the mobility range is 6.70×10 -4 ~9.98×10 -4 cm 2 / V·s) and impedance spectroscopy (mobility range is 3.59×10 -4 ~1.33×10 -3 cm 2 / V·s) results are similar; comparing the electron mobility measured in Example 3 and Comparative Examples 3 and 4, it can be seen that the electron mobility tested by this method (the mobility range is 7.00×10 -5 ~3.28×10 -4 cm 2 / V·s) and impedance spectroscopy (the mobility range is 2.99×10 -5 ~1.20×10 -4 cm 2 / V·s) and SCLC method (mobility at zero electric field strength 3.25×10 -5 cm 2 This indicates that the mobility measured by the method described in this aspect has high accuracy.

[0126] By comparing Table 1 and Table 4, it can be seen that although both Example 1 and Comparative Example 1 measure the hole mobility of the hole transport material HT-1, since the thickness of the electron blocking layer set in Comparative Example 1 is consistent with the thickness of the hole blocking layer, the electroluminescence time difference tested fluctuates greatly, the value is inaccurate, and the calculated mobility also has a large deviation. This is because the thickness of the electron blocking layer and the hole blocking layer does not meet the condition that the ratio of the thickness of the electron blocking layer to the hole blocking layer is ≥10, resulting in the electrons not being able to reach the light-emitting layer in priority to the holes, so that the obtained electroluminescence time difference is inaccurate, resulting in a large error in the measured hole mobility.

[0127] By comparing Table 3 and Table 5, it can be seen that although both Example 3 and Comparative Example 2 measure the electron mobility of the electron transport material ET-8, since the thickness of the hole blocking layer set in Comparative Example 2 is consistent with the thickness of the electron blocking layer, the electroluminescence time difference measured under some electric field intensities is negative, and thus the calculated electron mobility is an erroneous value of a negative value. This is because the thickness of the electron blocking layer and the hole blocking layer does not meet the condition that the ratio of the thickness of the hole blocking layer to the electron blocking layer is ≥5, so that the holes cannot preferentially reach the light-emitting layer, and it is impossible to obtain an accurate electroluminescence time difference, and thus an erroneous electron mobility value is measured.

[0128] It can be seen that when the ratio of the thickness of the electron blocking layer to the hole blocking layer does not meet the prerequisite that the mobility carrier to be measured enters the light-emitting layer later than another carrier, the test result is likely to be inaccurate. When the thickness of the electron blocking layer and the thickness of the hole blocking layer are optimized in Example 1 and Example 3, the mobility measured can be made more accurate. It can be seen that the organic semiconductor mobility test method of the present invention does not need to be limited to the prerequisite of measuring minority carrier mobility, and can be applied to the measurement of electron or hole mobility, which solves the deficiency that the traditional transient electroluminescence method is difficult to accurately measure hole mobility.

[0129] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention, and all these changes or substitutions should fall within the protection scope of the claims attached to the present invention.

Claims

1. A method for testing the mobility of an organic semiconductor, comprising the following steps: Step S1, preparing two organic electroluminescent devices, wherein the two organic electroluminescent devices respectively contain an organic semiconductor material to be tested with different thicknesses; Step S2, using a digital multimeter to measure the driving voltage of the two organic electroluminescent devices at the same current density; Step S3, using a transient spectrometer to measure the transient electroluminescence time of the two organic electroluminescent devices at different driving voltages; Step S4, calculating the mobility of the organic semiconductor material to be tested according to its thickness, driving voltage and transient electroluminescence time; Step S5, repeating the measurement steps S1-S4 to measure the mobility of the organic semiconductor under different current densities to obtain the mobility under different electric field strengths E; It is characterized in that, in the step S1, the two organic electroluminescent devices both include 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; when the hole mobility of the organic semiconductor material is tested, the hole transport layers of the two organic electroluminescent devices are prepared from the organic semiconductor material with the mobility to be tested, and the ratio of the thickness of the electron blocking layer to the hole blocking layer is ≥10; when the electron mobility of the organic semiconductor material is tested, the electron transport layers of the two organic electroluminescent devices are prepared from the organic semiconductor material with the mobility to be tested, and the ratio of the thickness of the hole blocking layer to the electron blocking layer is ≥5.

2. The method for testing the mobility of an organic semiconductor according to claim 1, characterized in that: In the step S1, when measuring the hole mobility of the organic semiconductor material, the ratio of the thickness of the electron blocking layer to the hole blocking layer is 10-50; the thickness of the electron blocking layer is 50-300 nm, and the thickness of the hole blocking layer is 5-30 nm.

3. The method for testing the mobility of an organic semiconductor according to claim 1, characterized in that: In the step S1, when measuring the electron mobility of the organic semiconductor material, the thickness ratio of the hole blocking layer to the electron blocking layer is 5-30; the thickness of the electron blocking layer is 5-30 nm, and the thickness of the hole blocking layer is 50-200 nm.

4. The method for testing the mobility of an organic semiconductor according to claim 2, characterized in that: In the step S1, when measuring the hole mobility of the organic semiconductor material, the electron transport layer is prepared from an n-doped electron transport composition.

5. The method for testing the mobility of an organic semiconductor according to claim 4, characterized in that: The n-doped electron transport composition comprises an n-type dopant and an electron transport material, wherein the n-type dopant is selected from one or a combination of Li, Na, K, Rb, Cs, Yb, Ag, Mg, Zn, Ta, and Pt; The electron transport material includes one of the structural formulas ET-1 to ET-40:

6. The method for testing the mobility of an organic semiconductor according to claim 5, characterized in that: The doping mass ratio of the n-dopant in the n-doped electron transport composition is 0.5% to 10%, and the thickness of the electron transport layer is 15 to 100 nm.

7. The method for testing the mobility of an organic semiconductor according to claim 3, characterized in that: When measuring the electron mobility of the organic semiconductor material, the hole transport layer is prepared from a p-doped hole transport composition.

8. The method for testing the mobility of an organic semiconductor according to claim 7, characterized in that: The p-doped hole transport composition is composed of a p-type dopant and a hole transport material, wherein the p-type dopant is selected from WO3, V2O5, MoO2, Co3O4 and one or more combinations of the structural formulas HI-1 to HI-17: The hole transport material is selected from one of the structural formulas HT-1 to HT-22:

9. The method for testing the mobility of an organic semiconductor according to claim 8, characterized in that: The doping mass ratio of the p-dopant in the p-doped hole transport composition is 0.5% to 10%, and the thickness of the hole transport layer is 30 to 150 nm.

10. The method for testing the mobility of an organic semiconductor according to claim 1, characterized in that: In step S1, in the two organic electroluminescent devices, the thickness of the organic semiconductor material to be tested is 50-350 nm, and the difference in thickness between the two is 50-300 nm.

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