Organic vertical molecular diode and its manufacturing method, and diode array manufacturing method

Abstract

The present invention discloses an organic vertical molecular diode and its preparation method, as well as a method for preparing a diode array. The diode includes a substrate, an insulating layer, a bottom electrode, an organic semiconductor film, and a top electrode. The metal layer is prepared on the surface of the insulating layer, and the prepared metal surface is smooth and has wettability to the solution for growing the organic semiconductor film. The organic semiconductor material is a conjugated organic small molecule with an alkyl side chain. The preparation method is as follows: growing an insulating layer on a substrate, preparing a bottom electrode on the insulating layer, and growing an organic semiconductor film on the bottom electrode; taking another substrate to prepare a top electrode; and transferring the top electrode metal to the organic semiconductor film. The organic vertical molecular diode prepared by the present invention achieves a record-breaking rectification ratio of up to 10 8 , the unit conductance exceeds 10 3 S / cm 2 The present invention also prepares an organic vertical molecular diode array, which achieves 100% yield and exhibits high uniformity.

Description

Technical Field

[0001] The present invention relates to a molecular diode, a preparation method thereof and a preparation method of a molecular diode array; in particular, to an organic vertical molecular diode and a preparation method thereof, and a preparation method of a diode array. Background Art

[0002] Organic molecular diodes have been widely used in circuit applications such as rectifiers, amplifiers, and energy harvesters. These applications require molecular diodes to have characteristics such as high rectification ratio, high conductivity, and high stability. Currently, the performance of molecular diodes has been greatly improved by designing new organic molecules, developing appropriate contact technology, optimizing contact interfaces, and charge injection. However, since metal deposition in traditional processes involves bombarding molecular films with high-energy metal particles, which to some extent destroys the contact between the metal and the semiconductor, the rectification ratio of molecular diodes usually does not exceed 10. 5 , which is lower than the standard of commercial Schottky or pn junction diodes.

[0003] Inserting a buffer layer between the semiconductor molecular film and the metal interface can be used to improve the contact. However, the inevitable thermal damage during metal deposition still leads to a large number of traps, creating a large potential barrier at the interface between the metal and the semiconductor, thereby reducing the current. In organic thin film diodes, it has been proven that using different metal contacts on both sides of the organic film can improve the rectification ratio. However, research on molecular diodes based on organic small molecules in terms of rectification ratio and conductivity improvement is still relatively lacking, especially regarding the optimization of metal-semiconductor contacts in molecular diodes.

[0004] Therefore, realizing a pinning-free metal-semiconductor intrinsic contact interface and rationally designing the metal-semiconductor contacts on both sides of the diode are of great significance for further improving the rectification ratio, conductance and other performance of organic molecular diodes. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide an organic vertical molecular diode with an ultra-high rectification ratio;

[0006] The second object of the present invention is to provide a method for preparing the above-mentioned organic vertical molecular diode;

[0007] The third object of the present invention is to provide a method for preparing an organic vertical molecular diode array using the above diodes.

[0008] Technical solution: The organic vertical molecular diode described in the present invention includes a substrate, an insulating layer, a bottom electrode, an organic semiconductor film and a top electrode; the bottom electrode is prepared on the surface of the insulating layer, and the surface of the prepared bottom electrode is smooth and has wettability to the solution for growing the organic semiconductor film; the organic semiconductor material is a conjugated organic small molecule with an alkyl side chain.

[0009] The bottom electrode is made of one of the following metals: titanium, platinum, gold, silver, or copper; and the top electrode contact layer is made of one of the following metals: silver, aluminum, gold, or platinum. By selecting the appropriate metal-semiconductor contact, the organic vertical molecular diode achieved a record-breaking rectification ratio of up to 10. 8 , the unit conductance exceeds 10 3 S / cm 2 .

[0010] The organic semiconductor material is 2,9-dihexylnaphtho[2,3-b]naphtho[2',3':4,5]thiophen[3,2-d]thiophene or 2,9-tetracosylnaphtho[2,3-b]naphtho[2',3':4,5]thiophen[3,2-d]thiophene. This conjugated organic small molecule with an alkyl side chain has good solubility in many organic solvents, facilitating thin film growth via liquid phase methods.

[0011] Wherein, the insulating layer is one of hafnium oxide, aluminum oxide or zirconium oxide thin film; preferably, the insulating layer is hafnium oxide, which is prepared by atomic layer deposition, has a smooth and uniform surface and good wettability, which is conducive to the growth of organic semiconductor thin films.

[0012] The method for preparing the above-mentioned organic vertical molecular diode comprises the following steps:

[0013] (1) growing an oxide as an insulating layer on a substrate;

[0014] (2) preparing a bottom electrode on the surface of the insulating layer, so that the surface of the bottom electrode is smooth and has wettability to the solution for growing the organic semiconductor film;

[0015] (3) preparing a growth solution, wherein the solvent of the solution used makes the bottom electrode wettable to the growth solution; adjusting growth parameters to grow an organic semiconductor thin film on the bottom electrode;

[0016] (4) Taking another substrate to prepare a top electrode, and then transferring the top electrode onto the organic semiconductor film to obtain the organic vertical molecular diode.

[0017] In step (1), the oxide obtained by atomic layer deposition preferably has a thickness of 20 to 30 nm, has extremely low surface roughness and a suitable number of nucleation sites, and is conducive to the large-area growth of organic semiconductor thin films. The method for growing the oxide is as follows: placing the substrate in an atomic layer deposition chamber, evacuating the chamber, raising the chamber temperature, and then introducing a metal source and an oxidizing source to in-situ deposit the oxide film.

[0018] Wherein, in step (2), the bottom electrode pattern can be obtained by ultraviolet or electron beam lithography, and the bottom electrode metal can be prepared by thermal evaporation or electron beam evaporation; preferably, the bottom electrode patterning is performed by electron beam lithography, and titanium, platinum, gold, silver or copper is prepared as the bottom electrode by electron beam evaporation. The bottom electrode metal surface prepared by the lower evaporation speed is smooth, which is conducive to the subsequent growth of the organic semiconductor film. The preferred evaporation speed is

[0019] In step (3), an organic semiconductor thin film is grown by a solution shearing method, and a prepared growth solution is injected into the gap between the substrate and the upper plate, and the upper plate is controlled to move continuously in one direction to obtain a large-area thin film; preferably, the solvent of the growth solution is one of toluene, chlorobenzene, and 1,2,3,4-tetrahydronaphthalene, and the saturated solution concentration is 0.25-0.45 mg / ml, and the saturated concentrations of the solutes 2,9-dihexylnaphthalene [2,3-b] naphtho [2',3':4,5]thiophene [3,2-d]thiophene and 2,9-tetracosylnaphthalene [2,3-b] naphtho [2',3':4,5]thiophene [3,2-d]thiophene are 0.25 mg / ml and 0.45 mg / ml respectively, and the growth solution is continuously heated at 80-85°C to ensure that the organic molecules are fully dissolved and will not Rapid degradation; preferably, the distance between the substrate and the upper plate of the device is set to 80-100 μm, and the inclination angle of the upper plate is 10-15°. The appropriate distance and angle make the meniscus of the solution conducive to the volatilization of the solvent, thereby forming a film of 2,9-dihexylnaphthalene [2,3-b] naphtho [2',3':4,5] thiophene [3,2-d] thiophene or 2,9-tetracosylnaphthalene [2,3-b] naphtho [2',3':4,5] thiophene [3,2-d] thiophene; adjusting the growth temperature and the scraping speed of the upper plate of the device to obtain a high-quality organic semiconductor single crystal thin film with controllable number of layers; the preferred growth temperature is 64-68°C, and the scraping speed of the upper plate is 2-2.5 μm / s. The lower scraping speed allows the organic small molecules to form a film in the volatile area. As the speed increases and the temperature decreases, the film thickness becomes thinner.

[0020] Wherein, in step (3), the contact angle of the solvent in the growth solution on the bottom electrode is in the range of 0 to 10°.

[0021] Among them, in step (4), a variety of metals can be selected as contact layers and support layers for preparing the top electrode, preferably silver, aluminum, gold or platinum; preferably, the top electrode patterning method adopts electron beam lithography, and the metal preparation method adopts electron beam evaporation.

[0022] Among them, in step (4), the top electrode transfer method is the van der Waals transfer method, which transfers the electrode to the organic semiconductor film without causing damage to the film, thereby protecting the organic semiconductor film from impact or thermal damage caused by high-energy metal particles during the metal deposition process.

[0023] A method for preparing an organic vertical molecular diode array using the above-mentioned diode comprises the following steps:

[0024] (1) growing an oxide as an insulating layer on a substrate;

[0025] (2) preparing a bottom electrode on the surface of the insulating layer;

[0026] (3) preparing a growth solution, wherein the solvent of the solution used makes the bottom electrode wettable to the growth solution; adjusting growth parameters to grow an organic semiconductor thin film on the bottom electrode;

[0027] (4) Prepare a top electrode on another substrate and cover it with a polymer encapsulation layer;

[0028] (5) The polymer encapsulation layer and the top electrode metal are removed from the substrate and transferred to the grown organic semiconductor film, and then the test area is patterned by electron beam lithography to produce the organic vertical molecular diode array.

[0029] Wherein, in step (4), the polymer encapsulation layer is polymethyl methacrylate or polyvinyl alcohol. The insulating polymer encapsulation layer will not affect the performance of the organic vertical molecular diode array, and at the same time can protect the array from the influence of water and oxygen in the air, thereby enhancing stability.

[0030] In step (5), a polydimethylsiloxane tape with a certain viscosity is used to peel off the polymer encapsulation layer and the top electrode metal from the substrate and remove them. The tape is heated at 90 to 100° C. for more than 10 minutes to make it lose its viscosity and release, separating it from the encapsulation layer and the top electrode. Then, a high-precision microscopic transfer platform is used to transfer the peeled encapsulation layer and the top electrode metal to the grown organic semiconductor film.

[0031] Wherein, in step (5), the test area is the probe test area of ​​the bottom electrode and the top electrode, and the packaging layer above the metal is patterned by electron beam lithography to obtain an exposed metal test area to facilitate subsequent probe testing.

[0032] Principle of the invention: The organic vertical molecular diode in the present invention is based on the direct growth of a metal bottom electrode to obtain a 1-4 layer high-quality ultra-thin organic semiconductor film. The nanometer-scale thickness of the organic semiconductor between the upper and lower electrodes greatly improves the on-state current of the vertical molecular diode and also provides a good platform for studying the intrinsic physical properties of the device. At the same time, the lossless ohmic contact between the top electrode Pt metal and the semiconductor transferred by the van der Waals transfer method also significantly improves the electrical properties such as the on-state current of the vertical molecular diode. The larger Schottky barrier between the bottom electrode Ti metal and the semiconductor on the other side suppresses the size of the off-state current, keeping it at the order of pA. Therefore, the appropriate metal-semiconductor contact on both sides of the vertical molecular diode, combined with the gentle preparation and transfer methods, realizes the electrical properties of the organic vertical molecular diode such as ultra-high rectification ratio and unit conductance.

[0033] Beneficial effects: Compared with the prior art, the present invention has achieved the following significant effects: (1) The organic semiconductor film is directly prepared in liquid phase on the bottom electrode, which simplifies the preparation process of the organic semiconductor film on the metal, and by selecting a suitable metal-semiconductor contact, the prepared organic vertical molecular diode achieves a high efficiency of up to 10 8 The rectification ratio is more than 10 3 S / cm 2 The unit conductance of the organic vertical molecular diode is 0.01, which breaks the record of molecular diodes and provides a reliable idea for improving the performance of molecular diodes; (2) The use of 1 to 4 layers of ultra-thin organic semiconductor films has great potential in exploring its intrinsic physical mechanisms such as microscopic carrier transport mechanism; (3) The prepared top electrode is transferred to the organic semiconductor film by the van der Waals transfer method, which avoids the damage of high-energy metal particles to the film during the evaporation process and improves the electrical properties such as the on-state current of the organic vertical molecular diode; (4) The preparation method of the organic vertical molecular diode array in the present invention uses an electron beam lithography patterning process, which can realize the patterning of any graphic and any area, and the array yield reaches 100%, showing high uniformity, and can be used to construct reliable and stable large-area circuits or array devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the structure of the organic vertical molecular diode prepared in Example 1;

[0035] Figure 2 This is a flow chart for preparing the organic vertical molecular diode prepared in Example 1;

[0036] Figure 3 This is an optical microscope image of the organic vertical molecular diode prepared in Example 1;

[0037] Figure 4 This is a transmission electron microscope image of the organic vertical molecular diode prepared in Example 1;

[0038] Figure 5 The curves of current density and rectification ratio versus voltage of the organic vertical molecular diode prepared in Example 1 are shown; wherein a is the current density-voltage curve of the organic vertical molecular diode, and b is the rectification ratio-voltage curve of the organic vertical molecular diode;

[0039] Figure 6 The curve of the current density of the organic vertical molecular diode prepared in Example 1 as a function of voltage; wherein a is the turn-on curve of the organic vertical molecular diode at a low voltage, and b is the breakdown curve of the organic vertical molecular diode at a high voltage;

[0040] Figure 7 Curves showing the change of current density versus voltage for organic vertical molecular diodes based on one to four layers of C6-DNTT prepared in Example 1;

[0041] Figure 8 UV-visible spectra and UV photoelectron spectra of C6-DNTT and metal of the organic vertical molecular diode prepared in Example 1;

[0042] Figure 9 This is a scanning electron microscope image of the organic vertical molecular diode array prepared in Example 2;

[0043] Figure 10 This is a curve showing the change in current density versus voltage for 50 devices of the organic vertical molecular diode array prepared in Example 2;

[0044] Figure 11 Distribution diagram of rectification ratio and ideality factor of 50 devices of the organic vertical molecular diode array prepared in Example 2;

[0045] Figure 12 The UV photoelectron spectrum of gold of the organic vertical molecular diode prepared in Comparative Example 1;

[0046] Figure 13 The curves showing the change of current density and rectification ratio with voltage for the organic vertical molecular diode prepared in Comparative Example 1 are as follows;

[0047] Figure 14 This is a curve showing the change of current density and rectification ratio of the organic vertical molecular diode prepared in Comparative Example 2 with voltage. DETAILED DESCRIPTION

[0048] The present invention is described in further detail below.

[0049] Example 1

[0050] The organic vertical molecular diode of the present invention is an organic vertical molecular diode based on a 2,9-dihexylnaphtho[2,3-b]naphtho[2',3':4,5]thiophene[3,2-d]thiophene molecular thin film with a Ti bottom electrode, wherein the 2,9-dihexylnaphtho[2,3-b]naphtho[2',3':4,5]thiophene[3,2-d]thiophene is denoted as C6-DNTT. The preparation method of the diode comprises the following steps:

[0051] (1) The oxide is obtained by atomic layer deposition, i.e. ALD. After cleaning the silicon substrate, it is placed in an atomic layer deposition chamber. The chamber is evacuated and the temperature is set to 150°C. The temperature is stabilized for 1 hour. Tetrakis(dimethylamino)hafnium is used as the metal source and water is used as the oxidation source. The procedure for growing hafnium oxide is as follows: first, a hafnium source pulse is applied, followed by a water source pulse. The pulse times of the hafnium source and water source are 300ms and 20ms respectively. The cleaning time between the two pulses is 30s. 180 cycles are set to start the growth of hafnium oxide with a thickness of about 25nm.

[0052] (2) The bottom electrode pattern is written on the hafnium oxide by electron beam lithography, and the bottom electrode width is 1 μm; then 30 nm titanium is evaporated by electron beam evaporation at a rate of about After removing the photoresist, a bottom electrode is obtained;

[0053] (3) Using the solution shearing method to grow organic semiconductor thin films: First, prepare the solution used for growth, use the solvent 1,2,3,4-tetralin to dissolve C6-DNTT, and prepare it to a saturated concentration of 0.45 mg / mL; then, inject the growth solution into the gap between the substrate and the upper plate, the distance between the substrate and the upper plate of the device is set to 100 μm, the tilt angle of the upper plate is 15°, the temperature of the upper plate and the lower plate is 64-68°C, the scraping speed of the upper plate is 2-2.5 μm / s, and the upper plate is controlled to move continuously in one direction through the electric displacement stage to complete the growth of the organic thin film; by controlling the temperature and scraping speed, 1 to 4 layers of controllable number of layers are obtained. C6-DNTT molecular film: When the upper and lower plate temperatures and the scraping speed are 64°C and 2.5μm / s, respectively, a single-layer C6-DNTT film with a thickness of approximately 2.5nm can be obtained; when the upper and lower plate temperatures and the scraping speed are 66°C and 2.5μm / s, respectively, a double-layer C6-DNTT molecular film with a thickness of ~5.5nm can be obtained; when the upper and lower plate temperatures and the scraping speed are 66°C and 2μm / s, respectively, a triple-layer C6-DNTT molecular film with a thickness of ~8.5nm can be obtained; when the upper and lower plate temperatures and the scraping speed are 68°C and 2μm / s, respectively, a quadruple-layer C6-DNTT molecular film with a thickness of ~11.5nm can be obtained;

[0054] (4) The top electrode pattern of the organic vertical molecular diode is written on a silicon wafer substrate using electron beam lithography, and the top electrode width is 2 μm. Then, 10 nm platinum / 190 nm gold is deposited by electron beam evaporation, and the top electrode is obtained after removing the photoresist. The contact layer of the top electrode is platinum and the support layer is gold. Then, the top electrode metal is transferred to the grown organic semiconductor film by van der Waals transfer, so that the organic semiconductor film is protected from impact or thermal damage caused by high-energy metal particles during the metal deposition process.

[0055] Figure 1 and Figure 2 They are respectively a structural schematic diagram and a preparation flow chart of the organic vertical molecular diode prepared in Example 1.

[0056] Figure 3 This is an optical microscope picture of the organic vertical molecular diode prepared in Example 1. The overlapping area of ​​the bottom electrode and the top electrode is only 1 μm*2 μm.

[0057] Figure 4 This is a transmission electron microscope image of the organic vertical molecular diode prepared in Example 1, showing that the diode structure is bottom electrode Ti / single-layer C6-DNTT molecular film / top electrode Pt. The thickness of the single-layer C6-DNTT molecular film is about 2.5 nm, and the contact interface between C6-DNTT and the top electrode Pt is clean and smooth, providing a good foundation for realizing a pinning-free metal-semiconductor intrinsic contact interface.

[0058] Figure 5 The curves of the current density and rectification ratio of the organic vertical molecular diode prepared in Example 1 as a function of voltage show that 4.8*10 3 A / cm 2 The high current density of 10 3 S / cm 2 High unit conductance, while the rectification ratio exceeds 10 8 , the ideality factor is about 1.3, close to 1, and it is a high-performance organic vertical molecular diode.

[0059] Figure 6 The current density-voltage curve of the organic vertical molecular diode prepared in Example 1 shows that the turn-on voltage of the diode is only 0.3V. The diode can operate at low voltage and can be used in low-power devices. The current density-voltage curve at high voltage shows that the bottom electrode Ti / single-layer C6-DNTT molecular film / top electrode Pt has a very high breakdown voltage, and the forward breakdown electric field reaches 7*10 7 V / cm, reverse breakdown electric field is as high as 1*10 8 V / cm, indicating that the prepared organic vertical molecular diode has good voltage resistance.

[0060] Figure 7 The current density versus voltage curves of the organic vertical molecular diodes based on one to four layers of C6-DNTT prepared in Example 1 show that the diode based on a single layer of C6-DNTT has the largest current density and rectification ratio, which can be attributed to the ultra-thin single layer of C6-DNTT having a thinner potential barrier, thus obtaining a larger on-state current.

[0061] Figure 8 The UV-visible light spectrum and UV photoelectron spectrum of C6-DNTT and metal of the organic vertical molecular diode prepared in Example 1, wherein a is the UV-visible light spectrum of C6-DNTT, b is the UV photoelectron spectrum of C6-DNTT, c is the UV photoelectron spectrum of platinum, and d is the UV photoelectron spectrum of titanium; the band gap of C6-DNTT is about 2.7 eV obtained from the maximum absorption peak position of the UV-visible light spectrum; the highest occupied molecular orbital and The lowest unoccupied molecular orbitals are -5.0eV and -2.3eV, respectively, and the work functions of metal Ti and Pt are -4.3eV and -5.6eV, respectively, indicating that there is a good ohmic contact between C6-DNTT and Pt, which is beneficial to improving the on-state current. There is a Schottky contact between C6-DNTT and Ti, and the Schottky barrier is large, which can greatly suppress the off-state current of the diode. Therefore, the bottom electrode Ti / single-layer C6-DNTT molecular film / top electrode Pt diode has an ultra-high rectification ratio and unit conductance.

[0062] Example 2

[0063] The organic vertical molecular diode array of the present invention is an organic vertical molecular diode array based on a single-layer 2,9-dihexylnaphtho[2,3-b]naphtho[2',3':4,5]thiophene[3,2-d]thiophene molecular film with a Ti bottom electrode, and its preparation method includes the following steps:

[0064] (1) After cleaning the silicon substrate, place it in an atomic layer deposition chamber, evacuate the chamber, set the temperature to 150°C, and stabilize the temperature for 1 hour. Use tetra(dimethylamino)hafnium as the metal source and water as the oxidation source. The procedure for growing hafnium oxide is as follows: first pass a hafnium source pulse, then pass a water source pulse. The hafnium source and water source pulse times are 300ms and 20ms, respectively. The cleaning time between the two pulses is 30s. Set 180 cycles and start growing hafnium oxide with a thickness of about 25nm.

[0065] (2) The bottom electrode array pattern was written on the hafnium oxide using electron beam lithography. The bottom electrode width was 1.5 μm. Then 30 nm titanium was deposited by electron beam evaporation at a rate of approximately After removing the photoresist, a bottom electrode array is obtained;

[0066] (3) Organic semiconductor thin films were grown using the solution shearing method: First, the growth solution was prepared, and the solvent 1,2,3,4-tetralin was used to dissolve C6-DNTT to a saturation concentration of 0.45 mg / mL; then, the growth solution was injected into the gap between the substrate and the upper plate. The distance between the substrate and the upper plate of the device was set to 100 μm, the tilt angle of the upper plate was 15°, the temperature of the upper and lower plates was 64°C, and the scraping speed of the upper plate was 2.5 μm / s. The upper plate was controlled to move continuously in one direction by an electric translation stage to complete the growth of a single-layer C6-DNTT molecular film with a thickness of about 2.5 nm.

[0067] (4) The top electrode array pattern of the organic vertical molecular diode is written on a silicon wafer using electron beam lithography, with a top electrode width of 1.5 μm. 10 nm platinum / 190 nm gold is then deposited by electron beam evaporation. After removing the photoresist, the top electrode array is obtained. Polymethyl methacrylate (PMMA) with a thickness of about 1 μm is spin-coated on the top electrode as an encapsulation layer, which serves as a support layer for electrode transfer while enhancing device stability.

[0068] (5) Using polydimethylsiloxane tape with a certain viscosity, the PMMA encapsulation layer and the top electrode metal array are peeled off from the silicon wafer. Polydimethylsiloxane is denoted as PDMS. The peeled encapsulation layer and the top electrode metal are transferred to the grown single-layer organic semiconductor film through a high-precision micro-transfer platform. After the stacking is completed, the PDMS is released by heating at 100°C for 10 minutes and separated from the encapsulation layer and the top electrode to obtain an organic vertical molecular diode array with a substrate / hafnium oxide / bottom electrode Ti / single-layer C6-DNTT molecular film / top electrode Pt / PMMA structure; finally, electron beam lithography is used to pattern the test area. The test area is the probe test area of ​​the bottom electrode and the top electrode. Electron beam lithography is used to pattern the PMMA above the metal to obtain exposed metal for subsequent probe testing.

[0069] Figure 9 This is a scanning electron microscope image of the organic vertical molecular diode array prepared in Example 2. The width of the bottom electrode and the top electrode in the array are both 1.5 μm. There are 50 devices in the array with a vertical and horizontal structure, including 10 rows of bottom electrodes and 5 columns of top electrodes.

[0070] Figure 10 The current density versus voltage curves of 50 devices of the organic vertical molecular diode array prepared in Example 2 show that the array has good uniformity and the on-state currents of the devices are basically the same, with a current density of about 140 A / cm 2 , the current deviation of 50 devices is about 3.9%.

[0071] Figure 11The distribution diagram of the rectification ratio (at a voltage of 3 V) and ideality factor of 50 devices of the organic vertical molecular diode array prepared in Example 2. The average values ​​of the rectification ratio and ideality factor are 1.2*10 7 and 1.24, the optimal values ​​of the ideal factor and the ideal factor are 2*10 7 and 1.11, so the prepared organic vertical molecular diode array also achieved a high rectification ratio and an ideality factor close to 1.

[0072] Comparative Example 1

[0073] The organic vertical molecular diode of the present invention is an organic vertical molecular diode based on a 2,9-dihexylnaphtho[2,3-b]naphtho[2',3':4,5]thiophene[3,2-d]thiophene molecular film with an Au bottom electrode.

[0074] On the basis of Example 1, the 30 nm titanium bottom electrode in step (2) of Example 1 was changed to 30 nm gold; the temperatures of the upper and lower plates and the scraping speed of the upper plate were set to 64°C and 2.5 μm / s in step (3) of Example 1, respectively, to grow a single-layer C6-DNTT molecular film; the remaining conditions were the same as in Example 1.

[0075] Figure 12 The ultraviolet photoelectron spectrum of gold in the organic vertical molecular diode prepared in Comparative Example 1 shows that the work function of metal Au is about -5.0 eV, indicating that there is also an ohmic contact between Au and C6-DNTT.

[0076] Figure 13 Figure 1 shows the current density and rectification ratio curves of the organic vertical molecular diode prepared in Comparative Example 1 as a function of voltage. (a) shows the current density-voltage curve for the organic vertical molecular diode with an Au bottom electrode, and (b) shows the rectification ratio-voltage curve for the organic vertical molecular diode with an Au bottom electrode. The current density-voltage curve shows that the off-state current of the Au bottom electrode / single-layer C6-DNTT molecular film / top electrode Pt is slightly lower than the on-state current. The rectification ratio-voltage curve shows that the diode's rectification ratio is less than 5, further demonstrating that the potential barrier between Au and C6-DNTT is negligible. The slight asymmetry in current under positive and negative voltages stems from the slight difference in the work functions of Au and Pt.

[0077] The ultra-low rectification ratio in Comparative Example 1 verifies the advantages of the bottom electrode Ti / single-layer C6-DNTT molecular film / top electrode Pt structure diode in Example 1 of the present invention in achieving ultra-high rectification ratio and high conductivity.

[0078] Comparative Example 2

[0079] The organic vertical molecular diode of the present invention is an organic vertical molecular diode based on a 2,9-dihexylnaphtho[2,3-b]naphtho[2',3':4,5]thiophene[3,2-d]thiophene molecular film with a Pt bottom electrode.

[0080] On the basis of Example 1, the 30 nm titanium bottom electrode in step (2) of Example 1 was changed to 30 nm platinum; the temperatures of the upper and lower plates and the scraping speed of the upper plate were set to 64°C and 2.5 μm / s in step (3) of Example 1, respectively, to grow a single-layer C6-DNTT molecular film; the remaining conditions were the same as in Example 1.

[0081] Figure 14 The current density and rectification ratio curves of the organic vertical molecular diode prepared in Comparative Example 2 vary with voltage; Figure a shows the current density-voltage curve for the organic vertical molecular diode with a Pt bottom electrode, and figure b shows the rectification ratio-voltage curve for the organic vertical molecular diode with a Pt bottom electrode. The current density-voltage curve shows that the off-state current and on-state current of the bottom electrode Pt / single-layer C6-DNTT molecular film / top electrode Pt are essentially equal. The rectification ratio-voltage curve shows that the diode's rectification ratio is approximately 1 because the metal-semiconductor contacts on the top and bottom of the diode are identical ohmic contacts. The symmetry of the current under positive and negative voltages stems from the essentially identical work function of the Pt on both sides; minor differences may be due to work function errors caused by different preparation methods for the top and bottom electrodes.

[0082] The rectification ratio close to 1 in Comparative Example 2 once again proves that the bottom electrode Ti / single-layer C6-DNTT molecular film / top electrode Pt structure diode in Example 1 of the present invention has great advantages in achieving ultra-high rectification ratio and high conductivity.

Claims

1. An organic vertical molecular diode, characterized in that The invention comprises a substrate, an insulating layer, a bottom electrode, an organic semiconductor film and a top electrode; the bottom electrode is prepared on the surface of the insulating layer, and the surface of the prepared bottom electrode is smooth and has wettability to the solution for growing the organic semiconductor film; the material of the organic semiconductor film is a conjugated organic small molecule with an alkyl side chain; the material of the organic semiconductor film is 2,9-dihexylnaphthalene[2,3-b]naphtho[2',3':4,5]thiophene[3,2-d]thiophene or 2,9-tetracosylnaphthalene[2,3-b]naphtho[2',3':4,5]thiophene[3,2-d]thiophene.

2. The organic vertical molecular diode according to claim 1, characterized in that: The bottom electrode is made of one of metals selected from titanium, platinum, gold, silver or copper; and the top electrode contact layer is made of one of metals selected from silver, aluminum, gold or platinum.

3. A method for preparing an organic vertical molecular diode according to claim 1, characterized in that: The following steps are involved: (1) Growing an oxide as an insulating layer on the substrate; (2) preparing a bottom electrode on the surface of the insulating layer, so that the bottom electrode surface is smooth and wettable to the solution for growing the organic semiconductor film; (3) preparing a growth solution, wherein the solvent of the solution used makes the bottom electrode wettable to the growth solution; adjusting the growth parameters to grow an organic semiconductor thin film on the bottom electrode; (4) Taking another substrate to prepare a top electrode, and then transferring the top electrode to the organic semiconductor film to obtain the organic vertical molecular diode.

4. The method for preparing an organic vertical molecular diode according to claim 3, wherein: In step (3), the contact angle of the solvent in the growth solution on the bottom electrode is in the range of 0 to 10°.

5. The method for preparing an organic vertical molecular diode according to claim 3, wherein: In step (3), the solvent in the growth solution is one of toluene, chlorobenzene, and 1,2,3,4-tetrahydronaphthalene.

6. The method for preparing an organic vertical molecular diode according to claim 3, wherein: In step (3), the concentration of the growth solution is 0.25~0.45 mg / mL.

7. The method for preparing an organic vertical molecular diode according to claim 3, wherein: In step (3), the adjusted growth parameters are: the distance between the substrate and the upper plate is set to 80~100 μm, the tilt angle of the upper plate is 10~15°, the growth temperature is 64~68℃, and the scraping speed of the upper plate is 2~2.5 μm / s.

8. A method for preparing an organic vertical molecular diode array using the diode according to claim 1, characterized in that: The following steps are involved: (1) Growing an oxide as an insulating layer on the substrate; (2) preparing a bottom electrode on the surface of the insulating layer; (3) preparing a growth solution, wherein the solvent of the solution used makes the bottom electrode wettable to the growth solution; adjusting the growth parameters to grow an organic semiconductor thin film on the bottom electrode; (4) Prepare a top electrode on another substrate and cover it with a polymer encapsulation layer; (5) The polymer encapsulation layer and the top electrode metal are removed from the substrate and transferred to the grown organic semiconductor film, and then the test area is patterned using electron beam lithography to produce the organic vertical molecular diode array.

9. The method for preparing an organic vertical molecular diode array according to claim 8, characterized in that: In step (4), the polymer encapsulation layer is polymethyl methacrylate or polyvinyl alcohol.

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