Humidity-regulated two-terminal lead-free perovskite artificial optical synapse device and preparation method

Abstract

The present invention discloses a humidity-regulated two-terminal lead-free perovskite artificial optical synaptic device and a preparation method thereof, wherein the lower electrode is sequentially spin-coated with a lead-free perovskite film, an organic ferroelectric polymer film, and an organic semiconductor film as an active functional layer, and then an upper electrode is thermally evaporated on the functional layer to form a vertical layered structure self-powered humidity-regulated two-terminal artificial synaptic device, and the preparation thereof specifically includes: preparation of a spin-coating liquid, spin-coating of a lead-free perovskite film and an organic ferroelectric polymer film, and evaporation of an organic semiconductor film and an upper electrode. Compared with the prior art, the present invention has the advantages of self-powered, all-optical regulation, and humidity regulation to simultaneously realize excitatory and inhibitory synaptic behaviors in the same device, and can simulate typical biological synaptic functions under the stimulation of light of a specific wavelength, and can be applied to construct an artificial neural network system, and the preparation method is simple and easy, low in cost, safe, and environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of artificial synaptic optoelectronic devices, and in particular to a self-powered, humidity-regulated, two-terminal lead-free perovskite artificial optical synaptic device and a preparation method thereof. Background Art

[0002] Due to the physical separation of storage and central processing units, traditional von Neumann architecture computers face severe challenges in the era of the Internet of Things. The realization of brain-like neuromorphic computing at the physical level mainly relies on artificial synaptic devices, which are the connections between neurons in neural networks. So far, various synaptic behaviors of biological synapses have been realized, including long-term plasticity (LTP), short-term plasticity (STP), and paired pulse facilitation (PPF). Although synaptic behaviors have been widely simulated, most neuromorphic devices rely on electrical stimulation to control conductance. In addition, human perceptual stimulation comes almost entirely from external sources (visual, tactile, olfactory, auditory, or pain receptors), which cannot be simulated by electrical stimulation alone. Compared with artificial synapses with electrical stimulation, optical signal stimulation has the advantages of high bandwidth, low power consumption, and low crosstalk, making it more attractive in neuromorphic vision systems.

[0003] All-inorganic lead-free double perovskites, especially Cs2AgBiBr6, have become one of the most promising alternatives to organic-inorganic hybrid perovskites in optoelectronic devices due to their environmental stability, low toxicity and simple solution film formation methods. They have good mechanical flexibility and are more conducive to applications in fields that require large-area, low-cost or flexible electronic devices. In addition, ferroelectric materials are functional materials with spontaneous polarization characteristics, whose polarization state can be continuously and reversibly adjusted by an external electric field and are non-volatile. Therefore, ferroelectric materials are considered to be one of the candidate materials for the new generation of memory. Three-terminal transistor devices usually use ferroelectric materials as gate insulators to control the conductivity changes of the device.

[0004] Humidity is the most common condition in nature and has an impact on human comfort, which suggests that humidity can be used as an external stimulus to regulate synaptic behavior. Most organic semiconductors such as pentacene are sensitive to humidity, and adsorbed water molecules can affect the generation, separation, and recombination of carriers. Therefore, humidity can be used as an additional stimulus to combine light pulses to regulate the synaptic performance of the device, which provides a new idea for multi-terminal control of synaptic plasticity and simplifies the preparation process. Summary of the invention

[0005] The purpose of the present invention is to provide a self-powered, humidity-regulated, two-terminal lead-free perovskite artificial optical synaptic device and a preparation method. By introducing an organic ferroelectric polymer film and organic pentacene, the device energy consumption is reduced and the multi-band light response capability is improved. The device can simulate the behavior of biological synapses with light signals as stimulation, and has a bidirectional response to light stimulation of different wavelengths (λ=445 nm / 660nm). This feature enables the device to simulate excitatory and inhibitory synaptic behaviors simultaneously through light stimulation, such as long-term potentiation (LTP) and long-term depression (LTD), double pulse facilitation (PPF) and depression (PPD), etc. In addition to light stimulation, humidity is used as an additional stimulus to adjust the synaptic performance of the device under 445 nm light. By adjusting the humidity, excitatory and inhibitory synaptic behaviors are successfully achieved under the stimulation of the same wavelength (445 nm). The device has the advantages of zero power consumption, fast response, long retention time, simple preparation method, low cost, safety, and environmental protection. It can be applied to artificial intelligence hardware and artificial neural network hardware.

[0006] The specific technical solution for achieving the purpose of the present invention is:

[0007] A humidity-regulated, two-terminal lead-free perovskite artificial optical synapse device is characterized in that a lead-free perovskite film, an organic ferroelectric polymer and a thermally evaporated organic semiconductor film are respectively spin-coated on the lower electrode as functional layers, and then a conductor is thermally evaporated on the functional layer as an upper electrode to form a vertical layered structure, a self-powered, humidity-regulated, two-terminal artificial synapse device, which is applied to the hardware of artificial intelligence and artificial neural networks. The lower electrode is made of indium tin oxide conductive glass; the upper electrode is a metal electrode made of gold, aluminum or platinum; the lead-free perovskite is cesium silver bismuth bromide or cesium silver bismuth chloride; the organic ferroelectric polymer is polyvinylidene fluoride or polyvinylidene fluoride-trifluoroethylene copolymer, and the organic semiconductor film is pentacene.

[0008] A method for preparing a humidity-regulated two-terminal lead-free perovskite artificial optical synapse device comprises the following steps:

[0009] 1. Cleaning of substrate

[0010] The substrate was ultrasonically cleaned in deionized water, acetone, ethanol and isopropanol for 10 to 20 minutes in sequence, and the surface of the substrate was dried with nitrogen and placed in a drying oven for later use.

[0011] 2. Preparation of spin coating solution

[0012] Cesium halide (CsX), silver halide (AgX) and bismuth halide (BiX3) were weighed at a molar ratio of 2:1:1 and dissolved in dimethyl sulfoxide (DMSO). The solution was heated to 65-70°C and stirred for 2-3 hours in an atmospheric environment to obtain a lead-free perovskite solution A with a concentration of 0.5 mol / L.

[0013] The organic ferroelectric polymer powder is dissolved in diethyl carbonate or butanone, and the solution is heated to 70-75° C. and stirred for 2-3 hours in an atmospheric environment to obtain a 10 mg-25 mg / mL colorless, clear and transparent organic ferroelectric polymer solution B; the concentration of the diethyl carbonate or butanone is 99%.

[0014] 3. Preparation of lead-free perovskite thin films, organic ferroelectric polymer thin films and organic semiconductor thin films

[0015] Take an appropriate amount of lead-free perovskite solution A with a pipette and drop it on the substrate cleaned in the rotating step (i) at a rotation speed of 500-3000 r / s for 50-60s. Move the spin-coated film into a vacuum drying oven for 5-10 minutes, and then anneal at 280-285°C for 5-10 minutes to obtain a lead-free perovskite film. After the thin plate on which the lead-free perovskite film has been deposited cools to room temperature, drop an organic ferroelectric polymer solution B at a rotation speed of 500-4000 r / s, and anneal at 135-140°C for 2-4 hours to prepare an organic ferroelectric polymer film on the lead-free perovskite film. Finally, deposit a layer of organic film on the annealed organic ferroelectric polymer film / inorganic perovskite film heterojunction by an organic thermal evaporation device, with a thickness of about 50-120nm and a deposition rate of 1.0-2.5 angstroms per second.

[0016] 4. Preparation of artificial synaptic devices

[0017] The mask is covered on the surface of the organic film, and a metal upper electrode with a thickness of 50 to 60 nanometers is obtained by thermal evaporation technology. The obtained device is a two-terminal artificial synapse controlled by ferroelectricity. The vacuum degree of the thermal evaporation is 2 to 6×10 -4 Pa, the deposition rate is 0.5~0.9 angstroms per second, and the evaporation time is 25~30 minutes.

[0018] The organic ferroelectric polymer is polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)); the lead-free perovskite is cesium silver bismuth bromide (Cs2AgBiBr6) or cesium silver bismuth chloride (Cs2AgBiCl6); the organic film is pentacene; the substrate is an indium tin oxide conductive glass as the lower electrode; the upper electrode is a metal such as gold, aluminum, platinum, etc.; the thickness of the lead-free perovskite film is 150~250 nanometers; the thickness of the organic ferroelectric polymer is 60~300 nanometers; the thickness of the pentacene organic film is 50-120 nm.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects and significant improvements:

[0020] 1) The built-in electric field of the ferroelectric polarization of organic ferroelectric polymer films is used to adjust the potential barrier between interfaces and control the generation and recombination of photogenerated electrons and photogenerated holes, thereby simplifying the device structure, reducing device energy consumption and increasing the retention time of the photocurrent.

[0021] 2) Combining the absorption characteristics of lead-free double perovskite and organic thin film, the device has a bidirectional response to 445 and 660 nm light pulses. Synaptic functions such as LTP, LTD, PPF and PPD were successfully simulated under all-light regulation.

[0022] 3) In addition, the photoelectric response of the device is affected by humidity. Humidity is used as an external stimulus and combined with 445 nm light pulses to regulate the synaptic performance of the device. Under the synergistic modulation of humidity and light pulses, excitatory and inhibitory synaptic plasticity are achieved in a single device. The preparation method has simple operation steps, easy-to-obtain raw materials, low cost, low energy consumption, high efficiency, and easy implementation; the entire preparation process is safe and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of the structure of the self-powered artificial optical synapse device prepared in Example 1;

[0024] Figure 2 A schematic diagram of the postsynaptic current of the device prepared in Example 1 after stimulation by a single light pulse at 445 nm and 660 nm wavelengths;

[0025] Figure 3 Schematic diagram of the device prepared in Example 1 of the present invention simulating excitatory and inhibitory synaptic behaviors after being stimulated at wavelengths of 445 nm and 660 nm respectively;

[0026] Figure 4 Schematic diagram of the device prepared in Example 1 combined with humidity regulation and 445 nm light pulse stimulation to simulate excitatory and inhibitory synaptic behaviors. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below in conjunction with specific examples and accompanying drawings. The process, conditions, reagents, experimental methods, etc. for implementing the present invention, except for the contents specifically mentioned below, are all common knowledge and common common sense in the art, and the present invention has no particular restrictions. The present invention is further elaborated below by examples, and its purpose is to more thoroughly understand the contents of the present invention, and all examples cited are not regarded as limitations on the scope of protection of the present invention.

[0028] Example 1

[0029] In this embodiment, pentacene is used as an organic semiconductor layer, polyvinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)) is used as an organic ferroelectric polymer, and cesium silver bismuth bromide (Cs2AgBiBr6) is used as a lead-free perovskite to prepare a self-powered artificial synaptic device based on pentacene, lead-free perovskite and organic ferroelectric polymer. The specific steps are as follows:

[0030] 1) The ITO substrate was ultrasonically cleaned in deionized water, acetone, ethanol and isopropanol for 20 minutes in sequence, and the surface of the substrate was blown dry with nitrogen and placed in a drying oven for standby use.

[0031] 2) Cesium bromide (CsBr), silver bromide (AgBr) and bismuth bromide (BiBr3) were weighed in a molar ratio of 2:1:1 and dissolved in 1 ml of dimethyl sulfoxide (DMSO). The solution was heated to 65°C in an atmospheric environment and stirred for 2 hours to obtain a clear, transparent yellow Cs2AgBiBr6 solution with a concentration of 0.5 mol / L.

[0032] 3) The polyvinylidene fluoride-trifluoroethylene copolymer powder was dissolved in diethyl carbonate to prepare a spin coating solution to obtain a P(VDF-TrFE) solution with a mass fraction of 1.5 wt%.

[0033] 4) Use a pipette to take 50 μL Cs2AgBiBr6 solution and drop it on the rotating ITO substrate at a rotation speed of 3000 r / s for 60 s; move the spin-coated film into a vacuum drying oven for 10 minutes, and then anneal it at 285°C for 10 minutes to obtain a Cs2AgBiBr6 film.

[0034] 5) After the thin plate with deposited Cs2AgBiBr6 film was cooled to room temperature, 70 μL of P(VDF-TrFE) solution was added to the prepared Cs2AgBiBr6 film at a rotation speed of 4000 r / s and annealed at 135°C for 4 hours to obtain a P(VDF-TrFE) / Cs2AgBiBr6 heterojunction film.

[0035] 6) Using organic thermal evaporation technology, a layer of organic semiconductor pentacene is deposited on the annealed P(VDF-TrFE) / Cs2AgBiBr6 heterojunction using an organic thermal evaporation device. The thickness is about 50-120 nm and the deposition rate is 1.0~2.5 angstroms per second to obtain a pentacene / P(VDF-TrFE) / Cs2AgBiBr6 heterojunction.

[0036] 7) A 50 nm thick metallic gold was deposited on the surface of the pentacene / P(VDF-TrFE) / Cs2AgBiBr6 heterojunction using thermal evaporation technology as the upper electrode to produce a self-powered humidity-controlled two-terminal lead-free perovskite artificial synaptic device.

[0037] See attached Figure 1 The self-powered humidity-controlled two-terminal lead-free perovskite artificial optical synapse device prepared in the above embodiment is a sandwich vertical structure.

[0038] See attached Figure 2 The artificial synaptic device prepared in the above embodiment was subjected to light illumination of 0.024 and 480 mW / cm 2 The behavior of biological synapses was simulated by applying blue light (445 nm) and red light (660 nm) with a fixed pulse width of 0.5 seconds. Under the 445 nm light pulse, the photocurrent instantly rose to ~ 60 picoamperes and then gradually decreased to the initial level. When the 660 nm light pulse was applied, the photocurrent instantly increased to the highest point and then gradually decreased. The measured postsynaptic current response shows that the device exhibits a bidirectional response under the irradiation of different wavelengths and has the ability to simulate the excitatory and inhibitory behaviors in biological synapses.

[0039] See attached Figure 3 , 10 pulses of different wavelengths were applied to the artificial synaptic device prepared in the above embodiment, and the test results were as follows: under the stimulation of 445 nm wavelength, the device current increased with the increase of the number of applied pulses, showing long-term potentiation behavior (LTP); under the stimulation of 660 nm wavelength, the device current decreased with the increase of the number of applied pulses, showing long-term depression behavior (LTD).

[0040] See attached Figure 4 , applying light pulses of the same intensity at different humidity to the artificial synaptic device prepared in the above embodiment, and obtaining current response curves at different humidity. The device can combine external humidity adjustment with 445 nm light pulse irradiation to simulate LTP and LTD behaviors at the same time.

[0041] The artificial synaptic device prepared in the above embodiment is subjected to the above performance test, and the results show that the device can simulate the function of biological neural synapses under dual-wavelength control and humidity control, respectively, and can be applied to construct an artificial neural network system.

[0042] The protection content of the present invention is not limited to the above embodiments. Without departing from the spirit and scope of the inventive concept, changes and advantages that can be thought of by those skilled in the art are included in the present invention and are protected by the attached claims.

Claims

1. A humidity-regulated two-terminal lead-free perovskite artificial optical synapse device, characterized in that: A lead-free perovskite film and an organic ferroelectric polymer film are sequentially spin-coated on the lower electrode as a semiconductor active functional layer, and then a conductor is thermally evaporated on the functional layer as an upper electrode to form a humidity-regulated two-terminal lead-free perovskite artificial synaptic device with a vertical layered structure, which can be used to construct an artificial neural network system; wherein the lower electrode is indium tin oxide conductive glass; the conductor is gold, aluminum or platinum; the lead-free perovskite is cesium silver bismuth bromide or cesium silver bismuth chloride; the organic ferroelectric polymer is polyvinylidene fluoride or polyvinylidene fluoride-trifluoroethylene copolymer; and the organic semiconductor is pentacene.

2. A method for preparing a humidity-regulated two-terminal lead-free perovskite artificial optical synapse device, characterized in that: The specific steps include:

1. Cleaning of substrate The substrate is ultrasonically cleaned in deionized water, acetone, ethanol and isopropanol solutions for 10 to 20 minutes in sequence, and then the surface of the substrate is blown dry with nitrogen and placed in a drying oven for standby use. The substrate is an indium tin oxide conductive glass as the lower electrode; 2. Preparation of spin coating solution The cesium halide, the silver halide, the bismuth halide and the dimethyl sulfoxide are mixed in a molar ratio of 2:1:1:28-50, and stirred at a temperature of 70-75° C. for 2-3 hours to prepare a lead-free perovskite solution A; Dissolving organic ferroelectric polymer powder in diethyl carbonate or butanone, stirring at 70-75° C. for 2-3 hours to obtain organic ferroelectric polymer solution B, wherein the mass volume ratio of the organic ferroelectric polymer to diethyl carbonate or butanone is 10 mg-25 mg: 1 ml; and the concentration of the diethyl carbonate or butanone is 99%; 3. Preparation of lead-free perovskite films Spin-coat the lead-free perovskite solution A on the cleaned substrate, vacuum dry for 5-10 minutes after spin coating, anneal at 280-285° C. for 5-10 minutes, cool naturally to room temperature, and prepare a lead-free perovskite film with a thickness of 120-200 nm on the upper electrode layer, wherein the spin speed is 500-3000 r / s and the spin time is 50-60 s; 4. Preparation of organic ferroelectric polymer films The organic ferroelectric polymer solution B is spin-coated on the lead-free perovskite film, annealed at 135-140°C for 2-4 hours after spin-coating, and then naturally cooled to room temperature; an organic ferroelectric polymer film with a thickness of 60-300 nm is prepared on the lead-free perovskite film, the spin speed is 500-4000 r / s, and the spin time is 20-30s; 5. Preparation of organic semiconductor thin films Depositing a layer of organic semiconductor film with a thickness of 50-120 nm on the annealed organic ferroelectric polymer film / inorganic perovskite film heterojunction by organic thermal evaporation deposition apparatus at a deposition rate of 1.0-2.5 Å / s; 6. Preparation of artificial synaptic devices The mask is covered on the surface of the organic ferroelectric polymer film, and an upper electrode with a thickness of 50-60 nm is evaporated to obtain the device which is the humidity-controlled two-terminal lead-free perovskite artificial synaptic device; the evaporation time is 25-30 minutes, and the vacuum degree of thermal evaporation is 2-6×10 -4 Pa, deposition rate is 0.5~0.9Å / s; where: The organic ferroelectric polymer is polyvinylidene fluoride or polyvinylidene fluoride-trifluoroethylene copolymer; The lead-free perovskite is Cs2AgBiBr6 or Cs2AgBiCl6; The organic semiconductor film is pentacene; The upper electrode is a metal electrode made of gold, aluminum or platinum.

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