CN114242892A - Organic hot electron transistor, preparation method thereof and LUMO energy level detection method - Google Patents
Organic hot electron transistor, preparation method thereof and LUMO energy level detection method Download PDFInfo
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Abstract
The invention relates to the field of organic electronics, in particular to an organic hot electron transistor, a preparation method thereof and a LUMO energy level detection method. The organic hot electron transistor comprises an emitter, a base and a collector; wherein an insulating layer is arranged between the emitter and the base, and an organic semiconductor layer is arranged between the base and the collector. The invention realizes the application of the hot electron transistor in the LUMO energy level detection technology of the organic semiconductor material for the first time through the structural improvement of the existing hot electron transistor. Meanwhile, the invention also provides a method for acquiring a hot electron energy spectrum by using the hot electron transistor, and provides a method for accurately extracting the LUMO energy level of the organic semiconductor material from the hot electron energy spectrum in situ. The invention not only fills the blank of research in the field, but also provides guidance for the research of charge transport behavior in the organic electronic device.
Description
Technical Field
The invention belongs to the field of organic electronics, and particularly relates to an organic hot electron transistor, a preparation method thereof and a LUMO energy level detection method.
Background
In the last decades, the research of organic optoelectronic devices has been made with remarkable success due to the remarkable advantages of organic semiconductor materials such as abundant optoelectronic functional properties, chemical tailorability, flexibility, and large-area preparation. A large number of electronic products such as organic light emitting diodes and organic photovoltaic cells are gradually commercialized, and the daily life of people is enriched; new electronic devices such as organic field effect transistors, photodetectors, lasers, and organic spintronics devices have attracted a wide global attention and have been impressively developed.
The organic semiconductor material is used as a core component of an organic optoelectronic device, and the Lowest Unoccupied Molecular Orbital (LUMO) and the Highest Occupied Molecular Orbital (HOMO) respectively control the injection and transportation processes of electrons and holes in the device, and directly determine the working principle of the organic electronic device. In order to optimize key performance parameters of organic electronic devices, the values of the LUMO and HOMO levels of the organic semiconductor material must be accurately measured.
Currently, for LUMO detection, a method of reflection electron spectroscopy is mainly used. Due to the low energy resolution and the destructive nature of the sample, the reflective electron spectroscopy cannot accurately test most organic semiconductor materials. In addition, the LUMO level of organic semiconductor materials, such as CN102928480A, is also tested by cyclic voltammetry, but since this method is strongly dependent on the experimental conditions of the test, including the solubility of the electrodes, solvents, electrolytes and even molecules, the reproducibility of the test is very poor (the bar for error of the test is usually ± 0.2 eV). Therefore, accurate measurement of the LUMO energy level of organic semiconductor materials has been a challenge that is difficult to solve in the art.
Disclosure of Invention
In a first aspect, the present invention provides an organic thermionic transistor of a novel structure that allows in-situ, accurate measurement of the LUMO level of an organic semiconductor material.
The organic hot electron transistor comprises an emitter, a base and a collector; wherein: an insulating layer is arranged between the emitter and the base, and an organic semiconductor layer is arranged between the base and the collector.
The thermionic transistors in the prior art have a vertical three-terminal electronic device structure consisting of an emitter, a base, and a collector. According to the invention, through the structural improvement of the existing thermionic transistor, the insulating layer is arranged between the emitter and the base, and the organic semiconductor layer is arranged between the base and the collector, so that the in-situ and accurate detection of the LUMO energy level of the organic semiconductor material is realized.
The invention firstly proposes that the thermionic transistor is used in the detection technology of the LUMO energy level of the organic semiconductor material, which not only makes up the blank of the research in the field, but also provides guidance for the research of charge transport behavior in the organic electronic device.
The working principle of the organic hot electron transistor is described by taking metal aluminum, gold and aluminum as an emitter, a base and a collector respectively as an example, and the working principle is as follows:
Al/Al2O3the tunnel junction of Al acts as an electron energy modulator, whose emitted hot electron energy is determined by an applied external bias voltage (E ═ eV)EB) (ii) a When high energy "hot" electrons cross the interfacial barrier, they are injected directly into the LUMO level of the organic semiconductor material, and finally a corresponding hot electron current signal is obtained at the collector (hot electron profile).
The specific layer structure of the organic hot electron transistor is as follows:
a substrate;
an emitter on the substrate;
an insulating layer on the emitter;
a base electrode on the insulating layer;
an organic semiconductor layer on the base electrode;
a collector on the organic semiconductor layer.
Furthermore, the invention researches and discovers that the thickness proportion of each layer structure has substantial influence on the detection precision. Since the number of electrons is significantly reduced after tunneling transport in the tunnel junction and ballistic transport in the base, when the thicknesses of the tunnel junction and the base are inappropriate, the hot electron current of the collector is small, and the detection result is inaccurate. In addition, due to the soft nature of the organic semiconductor material, when the organic semiconductor is thin, metal penetration during the evaporation of the top electrode is easily caused, and thus the detected signal is not a hot electron signal. Therefore, the invention provides that the thickness ratio of the emitter, the insulating layer, the base, the organic semiconductor layer and the collector is controlled to be (11-13): (1.5-2): (10-20): 100-200: (12-20) to avoid the above problem situation and help to improve the detection precision.
In a specific implementation, the thickness of the emitter ranges between 11-13nm, preferably 12 nm. The thickness of the insulating layer ranges between 1.5-2nm, preferably 1.6 nm. The thickness of the base is in the range of 10-20nm, preferably 15 nm. The thickness of the organic semiconductor layer ranges between 100-200nm, and is preferably 150 nm. The thickness of the collector is in the range of 12-20nm, preferably 15 nm.
In the organic hot electron transistor, the emitter, the base and the collector are all made of metal. The metal may be selected from one or more of aluminium, gold, cobalt, permalloy, silver or copper.
The insulating layer is made of aluminum oxide or aluminum semioxide AlOXOr magnesium oxide.
Further, the invention finds that the combination effect difference of different materials is relatively large and the influence on the test precision is obvious when the materials of all layers are specifically selected. Therefore, the emitting electrode is controlled to be made of Al; the insulating layer is made of AlOXAn in-situ oxidation formed and robust insulating layer; the base is Au, and Au is inert metal, is not easy to interact with an organic semiconductor and is an ideal base material; the collector is made of Al. Through the combination, the effects of all layers can be exerted to the maximum extent, higher test stability is kept, and the detection accuracy is improved.
The organic hot electron transistor of the present invention can be applied to the detection of the LUMO level of any film-formable organic semiconductor material. For example, in LUMO detection of organic semiconductor materials such as N2200, C60, PM6, PCE10, P3HT, PBDB-T, PBDB-T-2Cl, the method exhibits very high detection accuracy.
In a second aspect, the present invention also provides a method for manufacturing the organic hot electron transistor, including: forming an insulating layer between the emitter and the base; an organic semiconductor layer is formed between the base electrode and the collector electrode.
The invention adds the preparation of the insulating layer and the organic semiconductor layer on the basis of the existing preparation process of the organic hot electron transistor, and the obtained organic hot electron transistor with the new structure can accurately detect the LUMO energy level of the organic semiconductor material in situ.
Further, the insulating layer is formed by a plasma oxidation process; preferably, the plasma oxidation process is: the oxidation power is 12W, and the oxidation time is 1-5 minutes; .
The organic semiconductor layer can be formed by a thermal evaporation coating or spin coating method; preferably, the thermal evaporation coating 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.
In the organic hot electron transistor, the emitter, the base and the collector can be obtained by electron beam evaporation, thermal evaporation and magnetron sputtering processes.
Preferably, the collector is formed by a two-step deposition process; namely: first depositing aluminum with a thickness of 6nm on the organic semiconductor layer at a deposition rate of 0.1 angstrom/sec; subsequently, deposition of aluminum was continued at a deposition rate of 1 angstrom/sec for 6nm on the basis of the previous step, thereby forming a collector.
In a third aspect, the present invention also provides a method for obtaining a hot electron energy spectrum, which is obtained by the above hot electron transistor. The specific obtaining method comprises the following steps:
testing the electrical characteristics between the emitter and the base;
testing the electrical characteristics between the collector and the base;
the hot electron spectrum is obtained based on the electrical characteristics between the emitter-base and the electrical characteristics between the collector-base.
Further, the emitter-baseThe electrical property between the poles is the scan bias; the electrical characteristic between the collector-base is the test current. By applying a negative scan bias voltage V between the emitter and baseEBDetecting the corresponding thermionic current I at the collectorC-hot，VEB-IC-hotThe relationship is the hot electron spectrum.
In a fourth aspect, the present invention provides a method for detecting the LUMO level of an organic semiconductor material, which uses the organic hot electron transistor to obtain a hot electron energy spectrum, thereby obtaining the LUMO level of the organic semiconductor material.
The detection method comprises the following steps:
performing first order differential processing on the thermal electron energy spectrum;
a step of linear fitting in the hot electron spectrum;
obtaining an interface barrier of a base electrode/an organic semiconductor on the basis of linear fitting;
and a step of obtaining the LUMO level of the organic semiconductor on the basis of the interface barrier.
Further, the interface barrier is an interface barrier of the base electrode/the organic semiconductor layer, and the corresponding numerical value is an intersection point of a linear fitting straight line and two straight lines with current equal to zero.
The calculation formula of the LUMO energy level is as follows: LUMO ═ a- Φ; wherein A is the work function of the base electrode, and phi is the interface barrier of the obtained base electrode/organic semiconductor layer.
As one embodiment of the present invention, the detection method comprises the following steps:
(1) preparing an organic hot electron transistor; the method comprises the following steps: forming an insulating layer between the emitter and the base; forming an organic semiconductor layer of an organic semiconductor material to be tested between the base electrode and the collector;
(2) acquiring a hot electron energy spectrum;
(3) performing first order differential processing on the hot electron energy spectrum to determine a fitting area;
(4) obtaining an interface potential barrier through linear fitting;
(5) the LUMO energy level is calculated.
The invention has the following beneficial effects:
1. the invention enables the functionality of the LUMO level of the organic semiconductor material layer to be tested by combining the organic semiconductor material layer with a thermionic electron transistor.
2. The method is used for improving the LUMO energy level testing precision by optimizing the preparation process of the organic hot electron transistor and analyzing the hot electron energy spectrum by combining differential processing and linear fitting.
Test results show that the LUMO energy level of the organic semiconductor material can be obtained by preparing different organic semiconductor materials to obtain corresponding thermionic transistors and analyzing a thermionic energy spectrum by combining differential processing and linear fitting; and the results show very high accuracy of the test (+ -0.035 eV).
3. Compared with the traditional reflection electron energy spectrum and the cyclic voltammetry for testing the LUMO energy level of the organic semiconductor material, the detection method provided by the invention can better reflect the material characteristics in an actual electronic device, is simple and convenient to operate, and can be better combined with the application of an organic electronic device.
Drawings
Fig. 1 is a schematic view of the device structure of an organic hot electron transistor of the present invention.
FIG. 2 is a schematic diagram of Al/AlO in the organic thermionic transistor of the present inventionXGraph of Au tunnel junction I-V.
Fig. 3 is an I-V plot of an Au/organic semiconductor layer/Al junction in an organic thermionic transistor of the present invention.
Fig. 4 is a spectrum of the organic hot electron transistor of the present invention passing through an organic semiconductor layer.
FIG. 5 shows a schematic view of the present invention IC-hot-VEBFirst order differential curve of the curve.
FIG. 6 shows the formula I in the present inventionC-hot-VEBLinear fit data of the curve.
Detailed Description
In order to make the hot electron transistor, the testing method and the data processing designed in the present invention clearer, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the present invention.
It should be noted that the present invention is applicable to the study of LUMO energy levels of all organic semiconductor materials satisfying the following conditions: n-type small molecule semiconductors, n-type polymer semiconductors, p-type small molecule semiconductors, and p-type polymer semiconductors.
It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. Therefore, all other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without any creative effort belong to the protection scope of the present invention.
Example 1
An embodiment of the present invention provides an organic hot electron transistor, as shown in fig. 1, including:
an emitter 1 formed by metal on the surface of the substrate;
an insulating layer 2 formed on the emitter;
a base electrode 3 which is located on the insulating layer and is formed by metal;
an organic semiconductor layer 4 formed of an organic semiconductor and located on the base;
and a collector 5 formed of a metal and located on the organic semiconductor layer.
In one embodiment, the substrate may be a silicon wafer.
In a preferred embodiment, the emitter 1 and the collector 5 are both made of aluminum.
In a preferred embodiment, the insulating layer 2 is aluminum oxide formed by plasma oxidation.
As a preferred embodiment, the organic semiconductor 4 is an N-type polymer N2200.
The molecular structure of N2200 is:
in a preferred embodiment, the base 3 is gold.
The embodiment of the invention also provides a preparation step of the N2200-based organic hot electron transistor, which comprises the following steps:
(1) and cleaning the silicon wafer by using liquid detergent, secondary water, ethanol, acetone, isopropanol, piranha solution, secondary water and isopropanol in sequence to provide a clean substrate for preparing devices.
(2) Adopting electron beam evaporation degree to obtain a layer of 12nm emitter Al;
(3) the emitter Al is subjected to a Plasma oxidation process to obtain an oxide insulating layer AlO with the thickness of 1.6nmX(ii) a The deposition rate of the plasma oxidation process is 0.01-10 nm/min;
(3) by thermal evaporation in AlOXA layer of base electrode Au with the thickness of 15nm is deposited above the film;
(4) spin-coating a 150nm thick N2200 film (prepared with chlorobenzene into a solution with the concentration of 12.5mg/ml, and formed at 2000 rpm) on the base Au;
(5) evaporating a collector Al with the thickness of 15nm on the N2200 film by a thermal evaporation method; the deposition rate of the collector is 0.1 angstrom/second;
thus preparing Al/AlOXThe specific structure of the/Au/N2200/Al thermionic transistor is shown in FIG. 1.
The basic working principle of the hot electron transistor obtained in the embodiment is as follows: in making a suitable thermionic transistor, the energy of the initial electrons can be biased by the emitter base VEBSupplied electrostatic potential (eV)EB) To adjust.
The working principle of the hot electron transistor obtained in this embodiment can be described as follows:
when V isEBNegative bias on Al/Al2O3In the case of Au junction, electrons pass vertically through Al2O3Potential barrier, recorded as emitter current;
since the energy is much higher than the fermi level of gold, these injected electrons are often referred to as hot electrons, unlike fermi electrons; although most of the hot electrons will relax due to inelastic collision energy dissipation, some of the hot electrons can survive and bounce off the ultra-thin Au film without energy decayCarrying out channel transportation; in this case, if the applied energy-eVEBBelow the energy barrier of the Au/organic semiconductor layer, no hot electrons are injected into the polymer semiconductor, IC-hotIs zero;
on the contrary, if-eVEBWith energy matching to the LUMO, hot electrons will be injected into and pass through the LUMO of the organic semiconductor layer and be measured as I at the collectorC-hot；
Based on the above mechanism, information of the potential barrier Δ and the LUMO of the organic semiconductor layer is contained in I of the thermionic transistorC-hot-VEBAmong the characteristics.
The present embodiment also provides a method for obtaining a hot electron spectrum using an organic hot electron transistor, including:
carrying out electrical test on the organic hot electron transistor; the base electrode is always grounded; in Al/AlOXthe/Au tunnel junction was subjected to a current-voltage test and had a weak temperature dependence, as shown in fig. 2, indicating that a high quality tunnel junction was obtained.
The I-V curve of the Au/N2200/Al junction, which is subjected to a current-voltage test, exhibits a temperature dependence, as shown in FIG. 3(a), demonstrating the integrity of the N2200 thin film.
Applying a negative scan bias to the emitter of the thermionic transistor to detect the thermionic current at the collector, and obtaining IC-hot-VEBThe relationship is shown in FIG. 4 (a).
Calculation method of LUMO energy level:
to IC-hot-VEBThe curve is subjected to a first order differential operation to obtain a corresponding first order differential curve (as shown in fig. 5 (a));
taking the 'platform zone' voltage pair I in the first order differential curveC-hot-VEBCarrying out linear fitting on the curve to obtain a corresponding linear function;
extending the linear function to a fitted line, the extension line and IC-hotThe intersection point of the straight lines where 0 is located is the interface barrier of Au/N2200 (phi: the difference between the fermi level of the base Au and the LUMO level of N2200), as shown in fig. 6 (a);
the LUMO level of N2200 is directly obtained according to the formula LUMO- (5.3 eV-phi) (as shown in table 1); wherein 5.3eV is the work function of the base electrode Au.
Example 2
The p-type organic semiconductor PCE10 was selected as the subject of study to fabricate an organic thermionic transistor device and the LUMO level of the PCE10 material was tested.
The molecular structure of PCE10 is:
the experimental procedure was as in example 1.
Corresponding Al/AlOXAu tunnel junction, Au/PCE10/Al diode and Al/AlOXThe electrical characteristics of the/Au/N2200/Al thermionic transistor are shown in FIG. 3b, FIG. 4b, FIG. 5b and FIG. 6 b.
The measured LUMO values of PCE10 are shown in Table 1.
Example 3
The p-type organic semiconductor PM6 was selected as the subject of investigation to fabricate an organic thermionic transistor device and the LUMO level of the PM6 material was tested.
The molecular structure of PM6 is:
the experimental procedure was as in example 1.
Corresponding Al/AlOXAu tunnel junction, Au/PM6/Al diode, and Al/AlOXThe electrical characteristics of the/Au/PM 6/Al thermionic transistor are shown in FIG. 3c, FIG. 4c, FIG. 5c and FIG. 6 c.
The LUMO values of PM6 were measured and are shown in Table 1.
Examples 4 to 6
Organic semiconductor materials P3HT and PBDB-T, PBDB-T-2Cl are selected as research objects, organic hot electron transistor devices are prepared, and the LUMO energy level of the PM6 material is tested.
The experimental procedure was as in example 1.
The LUMO values obtained are shown in Table 1
Table 1 LUMO results of a portion of organic semiconductors tested using organic hot electron transistors.
| Type of material | LUMO(eV) | Error (eV) |
| Example 1N 2200 | -4.06 | ±0.03 |
| |
-3.43 | ±0.02 |
| Example 3 PM6 | -3.49 | ±0.02 |
| Example 4P 3HT | -2.77 | ±0.035 |
| Example 5 PBDB-T | -3.16 | ±0.03 |
| Example 6 PBDB-T-2Cl | -3.60 | ±0.02 |
Although the invention has been described in detail hereinabove with respect to a general description and specific embodiments thereof, it will be apparent to those skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.
Claims (10)
1. An organic hot electron transistor comprises an emitter, a base and a collector; an insulating layer is provided between the emitter and the base, and an organic semiconductor layer is provided between the base and the collector.
2. The organic thermionic transistor of claim 1 wherein the thickness ratio of the emitter, insulator, base, organic semiconductor layer, and collector is (11-13): (1.5-2): (10-20): 100-200: (12-20).
3. The organic thermionic transistor of claim 2, wherein the thickness of the emitter ranges between 11-13 nm;
the thickness range of the insulating layer is 1.5-2 nm;
the thickness of the base electrode ranges from 10nm to 20 nm;
the thickness of the organic semiconductor layer ranges from 90 nm to 200 nm;
the thickness of the collector is in the range of 12-20 nm.
4. The organic thermionic transistor of claim 3 wherein the insulating layer is one or more of aluminum oxide, semi-aluminum oxide, or magnesium oxide.
5. A method of fabricating an organic thermionic transistor as claimed in any one of claims 1 to 4, comprising: forming an insulating layer between the emitter and the base; an organic semiconductor layer is formed between the base electrode and the collector electrode.
6. The method of manufacturing an organic thermionic transistor according to claim 5, wherein the insulating layer is formed by a plasma oxidation process;
the organic semiconductor layer is formed by a thermal evaporation coating method or a spin coating method.
7. A method for obtaining a hot electron spectrum, characterized in that it is obtained by using a hot electron transistor according to any of claims 1-4.
8. A method of detecting the LUMO level of an organic semiconductor material, comprising obtaining a hot electron spectrum using the thermionic transistor of any one of claims 1 to 4, thereby obtaining the LUMO level of the organic semiconductor material.
9. The method according to claim 8, wherein the method comprises:
performing first order differential processing on the thermal electron energy spectrum;
a step of linear fitting in the hot electron spectrum;
obtaining an interface barrier of a base electrode/an organic semiconductor on the basis of linear fitting;
and a step of obtaining the LUMO level of the organic semiconductor on the basis of the interface barrier.
10. The method according to claim 9, wherein the corresponding value of the interfacial barrier between the base and the organic semiconductor is an intersection of a line fitted with a linear shape and two lines having a current equal to zero;
the calculation formula of the LUMO energy level of the organic semiconductor is as follows:
LUMO＝-(A-φ)；
wherein A is the work function of the metal base electrode, and phi is the interface barrier of the obtained Au/organic semiconductor.
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| CN115425144A (en) * | 2022-07-26 | 2022-12-02 | 安庆师范大学 | Preparation method of hot electron transistor, hot electron transistor prepared by using preparation method, application and application method |
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| CN115425144A (en) * | 2022-07-26 | 2022-12-02 | 安庆师范大学 | Preparation method of hot electron transistor, hot electron transistor prepared by using preparation method, application and application method |
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