Organic hot electron transistor and preparation method thereof, LUMO energy level detection method

Abstract

The present invention relates to the field of organic electronics, and specifically to an organic hot electron transistor, a preparation method thereof, and a LUMO energy level detection method. The organic hot electron transistor described in the present invention includes an emitter, a base, and a collector; wherein an insulating layer is provided between the emitter and the base, and an organic semiconductor layer is provided between the base and the collector. The present invention realizes the application of hot electron transistors in the detection technology of the LUMO energy level of organic semiconductor materials for the first time by improving the structure of existing hot electron transistors. At the same time, the present invention also provides a method for obtaining a hot electron energy spectrum using the hot electron transistor, and proposes a method for in-situ and accurate extraction of the LUMO energy level of an organic semiconductor material from the hot electron energy spectrum. The present invention not only fills the gap in research in this field, but also provides guidance for the study of charge transport behavior in organic electronic devices.

Description

Technical Field

[0001] The present invention belongs to the field of organic electronics, and in particular relates to an organic hot electron transistor and a preparation method thereof, and a LUMO energy level detection method. Background Art

[0002] Over the past few decades, research in organic optoelectronic devices has achieved remarkable success, thanks to the significant advantages of organic semiconductor materials, including their rich optoelectronic functional properties, chemical tailorability, flexibility, and large-area fabrication. A large number of electronic products, such as organic light-emitting diodes and organic photovoltaic cells, have gradually become commercialized, enriching our daily lives. New electronic devices, such as organic field-effect transistors, photodetectors, lasers, and organic spintronics, have garnered widespread attention worldwide and achieved impressive progress.

[0003] Organic semiconductor materials are core components of organic optoelectronic devices. Their lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) control the injection and transport of electrons and holes, respectively, and directly determine the operating principles of organic electronics. To optimize the key performance parameters of organic electronics, it is necessary to accurately measure the LUMO and HOMO energy levels of organic semiconductor materials.

[0004] At present, for the detection of LUMO, the method of reverse photoelectron spectroscopy is mainly used. Due to the low energy resolution of reverse photoelectron spectroscopy and the destructiveness to the sample, it is unable to accurately test the vast majority of organic semiconductor materials. In addition, the prior art also uses cyclic voltammetry to test the LUMO energy level of organic semiconductor materials, such as CN102928480A, but because this method is strongly dependent on the experimental conditions of the test, including electrodes, solvents, electrolytes and even the solubility of molecules, the reproducibility of its test is very poor (the test error bar is usually ± 0.2 eV). Therefore, accurately measuring the LUMO energy level of organic semiconductor materials has always been a challenge that is difficult to solve in this field. Summary of the Invention

[0005] In a first aspect, the present invention provides an organic hot electron transistor with a novel structure, which can accurately measure the LUMO energy level of an organic semiconductor material in situ.

[0006] The organic hot electron transistor of the present invention comprises an emitter, a base and a collector; wherein an insulating layer is provided between the emitter and the base, and an organic semiconductor layer is provided between the base and the collector.

[0007] Prior art hot electron transistors have a vertical three-terminal electronic device structure consisting of an emitter, a base, and a collector. The present invention improves on this structure by placing an insulating layer between the emitter and base, and an organic semiconductor layer between the base and collector, thereby enabling in-situ, precise detection of the LUMO energy level of the organic semiconductor material.

[0008] The present invention proposes for the first time the use of hot electron transistors in the detection technology of the LUMO energy level of organic semiconductor materials, which not only fills the research gap in this field, but also provides guidance for the study of charge transport behavior in organic electronic devices.

[0009] Taking metal aluminum, gold, and aluminum as the emitter, base, and collector, respectively, as examples, the working principle of the organic hot electron transistor of the present invention is explained as follows:

[0010] The tunnel junction composed of Al / Al2O3 / Al acts as an electron energy regulator, and the energy of the emitted hot electrons is determined by the applied external bias (E = -eV EB ); When high-energy "hot" electrons cross the interface potential barrier, they will be directly injected into the LUMO energy level of the organic semiconductor material, and finally the corresponding hot electron current signal (hot electron spectrum) will be obtained at the collector.

[0011] The specific layer structure of the organic hot electron transistor of the present invention is:

[0012] substrate;

[0013] an emitter located on the substrate;

[0014] an insulating layer located on the emitter;

[0015] a base electrode located on the insulating layer;

[0016] an organic semiconductor layer located on the base electrode;

[0017] A collecting electrode is located on the organic semiconductor layer.

[0018] Furthermore, the present invention has found that the thickness ratio of each layer structure has a substantial impact on the detection accuracy. Since the number of electrons will be significantly reduced after the tunneling transport in the tunnel junction and the ballistic transport in the base, when the thickness of the tunnel junction and the base is not appropriate, the thermal electron current of the collector will be small, resulting in inaccurate detection results. In addition, due to the soft nature of organic semiconductor materials, when the organic semiconductor is thin, it is easy to cause metal penetration during the top electrode evaporation process, which in turn causes the detected signal to be not a thermal electron signal. For this reason, the present invention proposes to control the thickness ratio of the emitter, insulating layer, base, organic semiconductor layer and collector to (11-13): (1.5-2): (10-20): 100-200: (12-20) to avoid the above-mentioned problems and help improve the detection accuracy.

[0019] In a specific embodiment, the thickness of the emitter is in the range of 11-13 nm, preferably 12 nm. The thickness of the insulating layer is in the range of 1.5-2 nm, preferably 1.6 nm. The thickness of the base is in the range of 10-20 nm, preferably 15 nm. The thickness of the organic semiconductor layer is in the range of 100-200 nm, preferably 150 nm. The thickness of the collector is in the range of 12-20 nm, preferably 15 nm.

[0020] In the organic hot electron transistor of the present invention, the emitter, base, and collector are all made of metal, which can be selected from one or more of aluminum, gold, cobalt, permalloy, silver, and copper.

[0021] The insulating layer is made of aluminum oxide, semi-aluminum oxide AlO X Or one or more of magnesium oxide.

[0022] Furthermore, the present invention found that the effects of different material combinations are relatively different when selecting the materials of each layer, which has a significant impact on the test accuracy. To this end, the present invention controls the material of the emitter to be Al; the material of the insulating layer to be AlO X , a strong insulating layer formed by in-situ oxidation; the base electrode is made of Au, an inert metal that is less likely to interact with organic semiconductors, making it an ideal base electrode material; and the collector is made of Al. This combination maximizes the effectiveness of each layer, maintains high test stability, and improves detection accuracy.

[0023] The organic hot electron transistor described in this invention can be applied to the detection of the LUMO energy level of any film-forming organic semiconductor material. For example, the method has demonstrated very high detection accuracy in the detection of LUMO energy levels of organic semiconductor materials such as N2200, C60, PM6, PCE10, P3HT, PBDB-T, and PBDB-T-2Cl.

[0024] In a second aspect, the present invention further provides a method for preparing the organic hot electron transistor, comprising: forming an insulating layer between the emitter and the base; and forming an organic semiconductor layer between the base and the collector.

[0025] The present invention adds the preparation of an insulating layer and an organic semiconductor layer to the existing preparation process of an organic hot electron transistor. The obtained organic hot electron transistor with a new structure can accurately detect the LUMO energy level of the organic semiconductor material in situ.

[0026] Furthermore, the insulating layer is formed by a plasma oxidation process; preferably, the plasma oxidation process is: oxidation power 12W, oxidation time 1-5 minutes;.

[0027] The organic semiconductor layer can be formed by thermal evaporation or spin coating. Preferably, the thermal evaporation process is 0.01-10 nm / min. The concentration of the organic semiconductor solution used in the spin coating method is 12-30 mg / ml.

[0028] In the organic hot electron transistor of the present invention, the emitter, base and collector can be obtained by electron beam evaporation, thermal evaporation and magnetron sputtering processes.

[0029] Preferably, the collecting electrode is formed by a two-step deposition process; that is: aluminum with a thickness of 6 nm is first deposited on the organic semiconductor layer at a deposition rate of 0.1 Å / s; then, aluminum is continued to be deposited with a thickness of 6 nm at a deposition rate of 1 Å / s based on the previous step, thereby forming a collecting electrode.

[0030] In a third aspect, the present invention further provides a method for obtaining a hot electron spectrum, which is obtained by the hot electron transistor described above. The specific method includes:

[0031] Test the electrical characteristics between emitter and base;

[0032] Test the electrical characteristics between collector and base;

[0033] Based on the electrical characteristics between the emitter and the base and the electrical characteristics between the collector and the base, a hot electron spectrum is obtained.

[0034] Furthermore, the electrical characteristic between the emitter and the base is the scanning bias voltage; the electrical characteristic between the collector and the base is the test current. EB , the corresponding hot electron current I is detected at the collector C-hot , V EB -I C-hot The relationship is the hot electron spectrum.

[0035] In a fourth aspect, the present invention provides a method for detecting the LUMO energy level of an organic semiconductor material, which utilizes the organic hot electron transistor to obtain a hot electron energy spectrum, and further obtains the LUMO energy level of the organic semiconductor material.

[0036] Wherein, the detection method includes:

[0037] Steps for performing first-order differential processing of thermal electron spectrum;

[0038] The steps of linear fitting in hot electron spectrum;

[0039] The base / organic semiconductor interface barrier step was obtained based on the linear fitting;

[0040] Steps to obtain the LUMO energy level of organic semiconductors based on interfacial barriers.

[0041] Furthermore, the interface potential barrier is the interface potential barrier of the base electrode / organic semiconductor layer, and the corresponding value is the intersection of the linear fitting line and the line where the current is equal to zero.

[0042] The calculation formula of the LUMO energy level is: LUMO=-(A-φ); wherein A is the work function of the base electrode, and φ is the obtained interface barrier of the base electrode / organic semiconductor layer.

[0043] As one of the specific embodiments of the present invention, the detection method comprises the following steps:

[0044] (1) Preparation of an organic hot electron transistor; comprising: forming an insulating layer between an emitter and a base; forming an organic semiconductor layer of an organic semiconductor material to be tested between the base and a collector;

[0045] (2) Obtaining thermal electron spectra;

[0046] (3) Perform first-order differential processing on the thermal electron energy spectrum to determine the fitting area;

[0047] (4) Linear fitting to obtain the interface potential barrier;

[0048] (5) Calculate and obtain the LUMO energy level.

[0049] The beneficial effects of the present invention are as follows:

[0050] 1. The present invention combines an organic semiconductor material layer with a hot electron transistor, thereby giving the hot electron transistor the functionality of testing the LUMO energy level of the organic semiconductor material layer.

[0051] 2. The present invention optimizes the preparation process of organic hot electron transistors and combines differential processing with linear fitting to analyze the hot electron energy spectrum to improve the accuracy of the method for testing the LUMO energy level.

[0052] The experimental results show that by preparing corresponding hot electron transistors from different organic semiconductor materials and combining differential processing with linear fitting to analyze the hot electron energy spectrum, the LUMO energy level of the organic semiconductor material can be obtained; and the results show that the test accuracy is very high (±0.035eV).

[0053] 3. Compared with traditional photoelectron spectroscopy and cyclic voltammetry for testing the LUMO energy level of organic semiconductor materials, the detection method of the present invention can better reflect the material properties in actual electronic devices, is easy to operate, and can be better integrated with the application of organic electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a schematic diagram of the device structure of the organic hot electron transistor of the present invention.

[0055] Figure 2 The Al / AlO in the organic hot electron transistor of the present invention X / Au tunnel junction IV curve.

[0056] Figure 3 FIG. 4 is an IV curve of the Au / organic semiconductor layer / Al junction in the organic hot electron transistor of the present invention.

[0057] Figure 4 This is an energy spectrum diagram of the organic hot electron transistor of the present invention through the organic semiconductor layer.

[0058] Figure 5 In the present invention, C-hot -V EB The first differential of a curve.

[0059] Figure 6 In the present invention, C-hot -V EB Linear fit of the curve to the data. DETAILED DESCRIPTION

[0060] In order to make the hot electron transistor, test method and data processing designed in the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention.

[0061] It should be noted that the present invention is applicable to the study of LUMO energy levels of all organic semiconductor materials that meet the following conditions: n-type small molecule semiconductors, n-type polymer semiconductors, p-type small molecule semiconductors, and p-type polymer semiconductors.

[0062] Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Therefore, all other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the scope of protection of the present invention.

[0063] Example 1

[0064] An embodiment of the present invention provides an organic hot electron transistor, such as Figure 1 Shown, including:

[0065] An emitter 1 formed of metal on the surface of the substrate;

[0066] an insulating layer 2 formed on the emitter;

[0067] a base electrode 3 located on the insulating layer and formed of metal;

[0068] An organic semiconductor layer 4 is formed on the base electrode and is made of an organic semiconductor;

[0069] A collecting electrode 5 is located in the organic semiconductor layer and is formed of metal.

[0070] In a specific embodiment, the substrate may be a silicon wafer.

[0071] As a preferred embodiment, the emitter 1 and the collector 5 are both made of aluminum.

[0072] As a preferred embodiment, the insulating layer 2 is aluminum oxide formed by plasma oxidation.

[0073] As a preferred embodiment, the organic semiconductor 4 is an n-type polymer N2200.

[0074] The molecular structure of N2200 is:

[0075]

[0076] As a preferred embodiment, the base electrode 3 is gold.

[0077] The embodiment of the present invention further provides a preparation step of an organic hot electron transistor based on N2200:

[0078] (1) Clean the silicon wafer with detergent, secondary water, ethanol, acetone, isopropyl alcohol, piranha solution, secondary water and isopropyl alcohol in sequence to provide a clean substrate for device preparation.

[0079] (2) Using electron beam evaporation, a 12nm emitter Al layer is obtained;

[0080] (3) The emitter Al is subjected to a plasma oxidation process to obtain an oxide insulating layer AlO with a thickness of 1.6 nm. X ; The deposition rate of the plasma oxidation process is 0.01 to 10 nm / min;

[0081] (3) Using thermal evaporation method, AlO X A 15nm layer of base Au is deposited on top of the film;

[0082] (4) Spin-coat a 150 nm thick N2200 film (prepared with chlorobenzene to a concentration of 12.5 mg / ml solution, and formed at 2000 rpm) on the Au base.

[0083] (5) A 15 nm thick collector Al layer was deposited on the N2200 film by thermal evaporation; the deposition rate of the collector was 0.1 Å / s;

[0084] Al / AlO was prepared X / Au / N2200 / Al hot electron transistor, the specific structure is as follows Figure 1 shown.

[0085] The basic working principle of the hot electron transistor obtained in this embodiment is: in a properly prepared hot electron transistor, the energy of the initial electron can be biased by the emission base V EB Provided electrostatic potential energy (eV EB ) to adjust.

[0086] The working principle of the hot electron transistor obtained in this embodiment can be described as follows:

[0087] When V EB When a negative bias is applied to the Al / Al2O3 / Au junction, electrons vertically pass through the Al2O3 barrier and are recorded as emitter current;

[0088] Since the energy is much higher than the Fermi level of gold, these injected electrons are often called hot electrons, which are different from Fermi electrons. Although most hot electrons relax due to inelastic collision energy dissipation, some hot electrons can still survive and be ballistically transported in the ultrathin Au film without energy decay. In this case, if the applied energy -eV EB If the energy barrier of the Au / organic semiconductor layer is lower than that of the Au / organic semiconductor layer, there will be no hot electron injection into the polymer semiconductor. C-hot is zero;

[0089] On the contrary, if -eV EB Matching the LUMO energy, the hot electrons will be injected into and pass through the LUMO of the organic semiconductor layer and measured at the collector as I C-hot ;

[0090] Based on the above mechanism, the information of the potential barrier Δ and the LUMO of the organic semiconductor layer is contained in the I C-hot -V EB Features.

[0091] This embodiment also provides a method for obtaining a hot electron energy spectrum using an organic hot electron transistor, comprising:

[0092] Electrical testing of organic hot electron transistors; the base is always grounded; in Al / AlO X / Au tunnel junction current-voltage test, with weak temperature dependence, such as Figure 2 As shown, it shows that high-quality tunnel junctions are obtained.

[0093] The current-voltage test of Au / N2200 / Al junction shows that its IV curve shows temperature dependence, such as Figure 3 As shown in (a), the integrity of the N2200 film is demonstrated.

[0094] A negative scanning bias is applied to the emitter of the hot electron transistor, and the hot electron current is detected at the collector to obtain I C-hot -V EB Relationships, such as Figure 4 As shown in (a).

[0095] Calculation method of LUMO energy level:

[0096] to I C-hot -V EB The first-order differential operation is performed on the curve to obtain the corresponding first-order differential curve (such as Figure 5 (as shown in (a));

[0097] Take the voltage of the “platform area” in the first-order differential curve to I C-hot -V EB The curve is linearly fitted to obtain the corresponding linear function;

[0098] This linear function is extended to the fitting straight line, and its extension line is C-hot =0 is the interface barrier of Au / N2200 (φ: the difference between the Fermi level of Au base and the LUMO level of N2200), as shown in Figure 2. Figure 6 (a)

[0099] According to the formula LUMO=-(5.3 eV-φ), the LUMO energy level of N2200 is directly obtained (as shown in Table 1); wherein 5.3 eV is the work function of the base electrode Au.

[0100] Example 2

[0101] The p-type organic semiconductor PCE10 was selected as the research object, organic hot electron transistor devices were prepared, and the LUMO energy level of the PCE10 material was tested.

[0102] The molecular structure of PCE10 is:

[0103]

[0104] The experimental operation is the same as in Example 1.

[0105] Corresponding Al / AlO X / Au tunnel junction, Au / PCE10 / Al diode, and Al / AlO X The electrical characterization of the / Au / N2200 / Al hot electron transistor is shown in Figures (3b), (4b), (5b) and (6b).

[0106] The measured LUMO values ​​of PCE10 are shown in Table 1.

[0107] Example 3

[0108] The p-type organic semiconductor PM6 was selected as the research object, organic hot electron transistor devices were prepared, and the LUMO energy level of the PM6 material was tested.

[0109] The molecular structure of PM6 is:

[0110]

[0111] The experimental operation is the same as in Example 1.

[0112] Corresponding Al / AlO X / Au tunnel junction, Au / PM6 / Al diode, and Al / AlO X The electrical characterization of the / Au / PM6 / Al hot electron transistor is shown in Figures (3c), (4c), (5c) and (6c).

[0113] The measured LUMO values ​​of PM6 are shown in Table 1.

[0114] Examples 4-6

[0115] Organic semiconductor materials P3HT, PBDB-T, and PBDB-T-2Cl were selected as research objects, organic hot electron transistor devices were prepared, and the LUMO energy level of PM6 materials was tested.

[0116] The experimental operation is the same as in Example 1.

[0117] The measured LUMO values ​​are shown in Table 1

[0118] Table 1 LUMO results of some organic semiconductors tested using organic hot electron transistors.

[0119] Material Type LUMO(eV) Error (eV) Example 1 N2200 -4.06 ±0.03 Example 2 PCE10 -3.43 ±0.02 Example 3 PM6 -3.49 ±0.02 Example 4 P3HT -2.77 ±0.035 Example 5 PBDB-T -3.16 ±0.03 Example 6 PBDB-T-2Cl -3.60 ±0.02

[0120] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. An organic hot electron transistor comprising an emitter, a base and a collector; characterized in that: An insulating layer is provided between the emitter and the base, and an organic semiconductor layer is provided between the base and the collector; the thickness ratio of the emitter, insulating layer, base, organic semiconductor layer and collector is (11-13): (1.5-2): (10-20): 100-200: (12-20); the thickness of the emitter is in the range of 11-13 nm.

2. The organic hot electron transistor according to claim 1, wherein The thickness of the insulating layer is in the range of 1.5-2 nm; The thickness of the base electrode ranges from 10 to 20 nm; The thickness of the organic semiconductor layer is in the range of 90-200 nm; The thickness of the collector is in the range of 12-20 nm.

3. The organic hot electron transistor according to claim 2, characterized in that The insulating layer is one or more of aluminum oxide, semi-aluminum oxide or magnesium oxide.

4. The method for preparing an organic hot electron transistor according to any one of claims 1 to 3, characterized in that: The method comprises: forming an insulating layer between the emitter and the base; and forming an organic semiconductor layer between the base and the collector.

5. The method for preparing an organic hot electron transistor according to claim 4, wherein: The insulating layer is formed by a plasma oxidation process; The organic semiconductor layer is formed by thermal evaporation or spin coating.

6. A method for obtaining a thermal electron spectrum, characterized in that: Obtained by using the hot electron transistor according to any one of claims 1-3.

7. A method for detecting the LUMO energy level of an organic semiconductor material, characterized in that: The hot electron energy spectrum is obtained by using the hot electron transistor according to any one of claims 1 to 3, and then the LUMO energy level of the organic semiconductor material is obtained.

8. The method for detecting the LUMO energy level of an organic semiconductor material according to claim 7, wherein: include: Steps for performing first-order differential processing of thermal electron spectrum; The steps of linear fitting in hot electron spectrum; The base / organic semiconductor interface barrier step was obtained based on the linear fitting; Steps to obtain the LUMO energy level of organic semiconductors based on interfacial barriers.

9. The method for detecting the LUMO energy level of an organic semiconductor material according to claim 8, wherein: The corresponding value of the interface potential barrier of the base electrode / organic semiconductor is the intersection of the linear fitting line and the line with zero current; The calculation formula of the LUMO energy level of the organic semiconductor is: LUMO = -(A-φ); Here, A is the work function of the metal base, and φ is the obtained Au / organic semiconductor interface barrier.

Images