Preparation method of perovskite thin film transistor based on self-assembled monomolecular layer

Abstract

The invention discloses a preparation method of a perovskite thin film transistor based on a self-assembled monomolecular layer, and relates to the technical field of perovskite. The preparation method comprises the following steps: (1) spin-coating a silicon wafer plated with silicon dioxide with a micromolecular solution dissolved in an organic solvent, and annealing at 100-120 DEG C for 10-15 min to obtain a multi-layer micromolecular film, the micromolecular solution being Br-2EPO or Br-2EPT; and (2) spin-coating an organic solvent on the multi-layer micromolecular film. According to the invention, two self-assembled monolayers Br-2EPO or Br-2EPT are introduced, and a phosphate group reacts with hydroxyl on the surface of a gate oxide to realize smaller hydroxyl density arrangement. And meanwhile, through the interaction of halogen bonds and Lewis acid-base, better lattice arrangement of perovskite is realized, the gate interface state is improved, and the internal trap density of the perovskite thin film transistor is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of perovskite, and in particular to a method for preparing a perovskite thin film transistor based on a self-assembled monolayer. Background Art

[0002] Based on the self-organization of perovskite, perovskite thin-film transistors are prepared by a spin coating solution process. The main steps include: 1. Clean the silicon wafer (p-type) with a silicon dioxide layer in acetone, deionized water and isopropanol solvent for 15 minutes; 2. Transfer the ultra-clean silicon wafer to a thermal evaporation chamber to evaporate the electrode, followed by UV treatment; 3. Spin-coat the evenly dissolved perovskite precursor solution on the UV-treated silicon wafer; 4. Place it on a 100°C heating table for annealing.

[0003] Currently, for perovskite transistors, silicon dioxide is mainly used as the gate oxide due to its integration compatibility. The gate oxide usually needs to be hydrophilized before perovskite deposition to ensure the formation of a coating, thereby generating excess hydroxyl groups on the gate oxide surface. On the one hand, carriers can be captured or scattered by hydroxyl groups as charged centers at the gate / channel interface. Although it can improve transistor mobility and operational stability, excess hydroxyl groups can also induce defects in the sequentially deposited perovskite layers, further complicating the gate-channel interface and deteriorating transistor performance. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a perovskite thin film transistor based on a self-assembled monolayer. The present invention utilizes the self-assembled monolayer to optimize the gate oxide surface and the atoms carried by the self-assembled monolayer to act on the perovskite layer. The designed interface layer can passivate hydroxyl groups and perovskite defects, increase the carrier mobility and switching ratio of the perovskite transistor, reduce the subthreshold swing and threshold voltage, and weaken the transistor hysteresis phenomenon and other advantages.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] The present invention provides a method for preparing a perovskite thin film transistor based on a self-assembled monolayer, comprising the following steps:

[0007] (1) spin coating a small molecule solution dissolved in an organic solvent on a silicon wafer coated with silicon dioxide, and annealing at 100-120° C. for 10-15 min to obtain a multilayer small molecule film, wherein the small molecule solution is Br-2EPO or Br-2EPT, and the concentration of the small molecule solution is 0.5-5 mg / mL;

[0008] (2) Spin-coat the organic solvent onto the multi-layer small molecule film.

[0009] The present invention introduces two self-assembled monolayers (SAM) Br-2EPO or Br-2EPT, and the phosphate groups react with the hydroxyl groups (-OH groups) on the surface of the gate oxide to achieve a smaller hydroxyl density arrangement. At the same time, the perovskite achieves a better lattice arrangement through halogen bonds and Lewis acid-base interactions, improves the gate interface state and effectively reduces the internal trap density of the perovskite thin film transistor.

[0010] The present invention forms a multi-layer Br-2EPO or Br-2EPT small molecule film on silicon dioxide by spin coating a small molecule solution on a silicon wafer, wherein the phosphate groups in the bottom Br-2EPO or Br-2EPT small molecules can have a strong anchoring effect with the silicon dioxide substrate and form an orderly arranged single molecule film, and the remaining Br-2EPO or Br-2EPT that does not participate in the anchoring is accumulated on the anchored single molecule film in a disordered state. Then, ethanol is spin coated on the multi-layer Br-2EPO or Br-2EPT small molecule film to wash away the Br-2EPO or Br-2EPT small molecules that are not connected to silicon dioxide, so that the single molecule deposition on the silicon wafer can be maximized.

[0011] Br-2EPT is (2-(3,7-dibromo-10H-phenothiazin-10-yl)ethyl)phosphonic acid, Br-2EPO is (2-(3,7-dibromo-10H-phenothiazin-10-yl)ethyl)phosphonic acid;

[0012] The English names of Br-2EPT and Br-2EPO are as follows:

[0013] Br-2EPT: (2-(3,7-Dibromo-10H-phenothiazin-10-yl)ethyl)phosphonic acid;

[0014] Br-2EPO: (2-(3,7-Dibromo-10H-phenoxazin-10-yl)ethyl)phosphonic acid.

[0015] Br-2EPT and Br-2EPO are two different organic compounds with molecular weights of 465.10 and 449.03, respectively. The difference between the two compounds mainly comes from the core heteroatom connecting the two benzene rings, sulfur (S) in Br-2EPT and oxygen (O) in Br-2EPO. The polarizability of sulfur (S) atoms is greater than that of oxygen (O) atoms, which will lead to a smaller interface trap density and longer carrier lifetime in Br-2EPT, resulting in higher transistor mobility and stability.

[0016] If the concentration of the small molecule solution is less than 0.5 mg / mL, the small molecules will not be able to completely cover the substrate, and the exposed hydroxyl groups will still affect the uniformity of the film and the performance of the device. If the concentration of the small molecule solution is greater than 5 mg / mL, the small molecules on the substrate will agglomerate and increase the roughness of the substrate, which will not only affect the quality of the perovskite film, but also further affect the performance and stability of the optoelectronic device.

[0017] Preferably, in step (1), the concentration of the small molecule solution is 1-3 mg / mL.

[0018] More preferably, in step (1), the concentration of the small molecule solution is in the range of any one or both of 1 mg / mL, 1.5 mg / mL, 2 mg / mL, 2.5 mg / mL, and 3 mg / mL.

[0019] Preferably, in step (1), the rotation speed during spin coating is 3000-4000 rpm, and the spin coating time is 25-30 s.

[0020] Preferably, in step (1), the silicon wafer coated with the silicon dioxide layer is pretreated as follows:

[0021] The silicon wafer coated with the silicon dioxide layer is cleaned in acetone, deionized water and isopropanol solvent respectively; then the cleaned silicon wafer is transferred to a thermal evaporation chamber to evaporate the electrode, and then UV treatment is performed.

[0022] Preferably, the organic solvent includes at least one of ethanol and isopropanol.

[0023] Preferably, in step (2), the rotation speed during spin coating is 4000-45000 rpm, and the spin coating time is 30-35 s.

[0024] Preferably, in step (2), the amount of the organic solvent used is 100-500 uL.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] For the passivation of interface defects of perovskite thin film transistors, the present invention introduces a self-assembled monolayer of Br-2EPO or Br-2EPT and deposits it in the gate oxide through self-assembly to achieve hydroxyl passivation on the substrate surface and enhance the quality of the perovskite film. Since the substrate maintains a sufficiently small number of hydroxyl groups during the spin coating of the perovskite film and the halogen atoms and Lewis base groups on the self-assembled molecular material can act on the perovskite, the probability of lattice distortion of the film is reduced while the bonding with the substrate is tighter, and the internal defects of the perovskite thin film transistor and the corresponding trap-state induced carrier recombination are effectively suppressed. In addition, the interface modification treatment also reduces the hysteresis of the output and transfer characteristics by reducing the number of residual starting materials and related ions in the perovskite film, thereby improving the overall performance of the transistor. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 (A) is a schematic diagram of the preparation process of the thin film transistor before self-assembled molecular layer modification, (B) is the transistor transfer characteristic curve, and (C) is the transistor output characteristic curve.

[0028] Figure 2 (A) is a schematic diagram of the preparation process of thin film transistors after self-assembled molecular layer modification, (B) is the transfer characteristic curve of Br-2EPO modified thin film transistor, (C) is the transfer characteristic curve of Br-2EPT modified thin film transistor, (D) is the output characteristic curve of Br-2EPO modified thin film transistor, and (E) is the output characteristic curve of Br-2EPT modified thin film transistor.

[0029] Figure 3 (A) is the electron energy spectrum of the P element on Br-2EPO, (B) is the electron energy spectrum of the P element on Br-2EPT, (C) is the contact angle test diagram of the silicon wafer before and after self-assembled molecular layer modification, (D) is the XPS diagram of Si 2p on the gate oxide before and after self-assembled molecular layer modification, and (E) is the XPS diagram of O1s on the gate oxide before and after self-assembled molecular layer modification.

[0030] Figure 4(A) is the change in the peak position of Br 3d on Br-2EPO before and after the mixed perovskite, (B) is the change in the peak position of Br 3d on Br-2EPT, (C) is the change in the peak position of S2p on Br-2EPT, (D) is the XPS image of the film before self-assembled molecular layer modification, (E) is the XPS image of the film modified with Br-2EPO, (F) is the XPS image of the film modified with Br-2EPT, (G) is the SEM image of the film before self-assembled molecular layer modification, (H) is the SEM image of the film modified with Br-2EPO, (I) is the SEM image of the film modified with Br-2EPT, (J) is the AFM image of the film before self-assembled molecular layer modification, (K) is the AFM image of the film modified with Br-2EPO, and (L) is the AFM image of the film modified with Br-2EPT.

[0031] Figure 5 (A) is the XRD test of the three films, (B) is the PL test of the three films, (C) is the PLQY test of the three films, (D) is the in-situ PL test of the three films, and (E) is the TrPL test of the three films.

[0032] Figure 6 (A) is the subthreshold swing diagram of perovskite thin film transistor, and (B) is the defect state density.

[0033] Figure 7 There are three types of transistor dynamic electrical switching tests.

[0034] Figure 8 (A) is the time transfer characteristic test of thin film transistor under different bias before self-assembled molecular layer modification, (B) is the time transfer characteristic test of thin film transistor modified with Br-2EPO, and (C) is the time transfer characteristic test of thin film transistor modified with Br-2EPT.

[0035] Fig. 9 (A) is the transfer characteristics test of thin film transistors before self-assembled molecular layer modification at different placement times, (B) is the transfer characteristics test of thin film transistors modified with Br-2EPO at different placement times, and (C) is the transfer characteristics test of thin film transistors modified with Br-2EPT at different placement times.

[0036] Fig.10 (A) is the transfer characteristics test of thin film transistor at different gate voltages before self-assembled molecular layer modification, (B) is the transfer characteristics test of thin film transistor at different gate voltages modified by Br-2EPO, (C) is the transfer characteristics test of thin film transistor at different gate voltages modified by Br-2EPT, (D) is the transfer characteristics test of thin film transistor at ultra-low gate voltage before self-assembled molecular layer modification, (E) is the transfer characteristics test of thin film transistor at ultra-low gate voltage modified by Br-2EPO, and (F) is the transfer characteristics test of thin film transistor at ultra-low gate voltage modified by Br-2EPT. DETAILED DESCRIPTION

[0037] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the protection scope and implementation methods of the present invention are not limited thereto.

[0038] Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0039] Example 1

[0040] A method for preparing a perovskite thin film transistor based on a self-assembled monolayer comprises the following steps:

[0041] (1) Pre-treating the silicon wafer: cleaning the silicon wafer with the silicon dioxide layer in acetone, deionized water and isopropanol solvent for 15 minutes respectively; then transferring the cleaned silicon wafer to a thermal evaporation chamber to evaporate the electrode, and then performing UV treatment;

[0042] (2) Spin coating a small molecule solution dissolved in ethanol on a pre-treated silicon dioxide wafer, annealing at 100° C. for 10 min to obtain a multilayer small molecule film, wherein the small molecule solution is Br-2EPO (manufacturer: Taiwan Jiguang Technology), and the concentration of the small molecule solution is 1 mg / mL; the rotation speed during spin coating is 4000 rpm, and the spin coating time is 30 s;

[0043] (3) Then, 200 uL of ethanol was spin-coated on the multi-layer small molecule film to obtain a perovskite thin film transistor. The spin-coating speed was 4000 rps and the spin-coating time was 30 s.

[0044] Example 2

[0045] The only difference from Example 1 is that the small molecule solution is Br-2EPT (manufacturer: Taiwan Jiguang Technology).

[0046] Two-dimensional tin-based perovskite (PEA 2 Sn 4 ) transistor as an example, the preparation process of one-step deposition on silicon wafer is as follows Figure 1 As shown in Figure A, the chemical properties of the gate interface state largely determine the transfer characteristics and output characteristics of the transistor.

[0047] Since hydrophilic treatment induces explosive growth of hydroxyl groups on the gate oxide surface, it causes large hysteresis in the transistor transfer curve and a reduction in the on-off ratio, followed by the loss of other transistor parameter performances, such as threshold voltage and subthreshold swing, etc. Figure 1 B, the output characteristic curve is as follows Figure 1 As shown in C.

[0048] Figure 2 A is the preparation flow chart of the interface state modified transistor. The self-assembled molecules (Br-2EPO and Br-2EPT) can achieve the function of tightly connecting the substrate and the perovskite layer, which plays a vital role in improving the stability of the transistor. The transfer characteristic curve of the perovskite transistor after interface modification is shown in Figure 2 B, 2C, the output characteristic curve is as follows Figure 2 D, 2E. This invention makes perovskite transistors have great potential in future display, sensor and storage technologies.

[0049] Energy dispersive spectrometer (EDS) analysis of P element confirmed the deposition of Br-2EPO and Br-2EPT on silica ( Figure 3 A, B). The hydrophobic effect of Br-2EPO and Br-2EPT is also retained on silica, which is beneficial to enlarge the perovskite nucleation site and make the film growth more dense ( Figure 3 C). XPS spectroscopy showed that Br-2EPO and Br-2EPT small molecules achieved the passivation of hydroxyl groups ( Figure 3 D, E).

[0050] The halogen atoms (Br) and Lewis base (S) in the Br-2EPT small molecule can effectively interact with the uncoordinated electrons in the Sn atom. The XPS electron energy spectrum shows that Br-2EPT has a passivation effect on the perovskite film ( Figure 4 A, B, C). And through the action of functional groups, the tetravalent tin inside the perovskite layer after interface modification is significantly suppressed ( Figure 4 D, E, F), the divalent tin content increased from 58.29% to 68.66%. From the scanning electron microscopy (SEM) results, it can be seen that after Br-2EPT small molecule passivation, the grain size of the perovskite film increased significantly ( Figure 4 G, H, I), the atomic force microscopy (AFM) results show that the original perovskite film exhibits a high roughness of 21.4nm ( Figure 4 J). In comparison, the perovskite films modified by self-assembled small molecules showed lower roughness, which were 12.9nm and 11.9nm respectively ( Figure 4 K, L).

[0051] The X-ray diffractometer (XRD) results show that the half-peak width is reduced, which proves that the film has better crystallinity ( Figure 5 A). Steady-state PL results show that the PL intensity of the film after interface modification is higher ( Figure 5 B). The photoluminescence quantum yield (PLQY) results show that the PLQY value after interface modification is increased to twice that of the original film ( Figure 5C). In situ PL spectroscopy shows that self-assembled small molecules can slow down the crystallization rate of perovskite ( Figure 5 D). Time-resolved photoluminescence (TRPL) spectroscopy shows that the interface-modified films have longer carrier lifetimes ( Figure 5 E), indicating the reduction of non-radiative recombination at the interface.

[0052] Further analysis of the internal defect state of the transistor is carried out through subthreshold swing data ( Figure 6 A) The defect state density is calculated. It can be seen that the internal defect state density of the transistor modified by Br-2EPO is reduced to the original internal defect state density of the transistor modified by Br-2EPO from 7.42×10 12 Reduced to 6.72×10 12 The internal defect state density of the transistor modified by Br-2EPO was significantly reduced to 4.19×10 12 ( Figure 6 B).

[0053] Dynamic electrical switching tests were performed to characterize the working stability of the two thin-film transistors before and after self-assembled molecular layer modification ( Figure 7 ), all three devices provided highly repeatable on / off current states over more than 1000 electrical cycles. The Br-2EPT-modified FETs exhibited highly reproducible on / off current states under the same conditions, with excellent electrical performance reproducibility. The Br-2EPO-modified FETs showed a slight attenuation. The FETs without SAMs modification showed a very significant current attenuation during the electrical cycle. The operational stability of the transistors was evaluated by long-term bias voltage measurements under constant negative gate and drain voltages (VGS = -40 V, VDS = -40 V). Figure 8 A, B, C), the VTH change of the transistor modified by Br-2EPT is less than 1.5V after continuous bias for more than 1800s. In contrast, the IDS value of the original device degraded rapidly after 1800s bias voltage test, and the VTH shifted negatively by a large margin (14V). The IDS decay was only 5%. The environmental stability of the transistor was further evaluated by measuring the transfer characteristic curves of the transistor placed for 24h and 5 days ( Fig. 9 A, B, C). The original device basically lost its transistor characteristics after 5 days of storage in the N2 glove box, while the interface-modified device still maintained high transistor mobility and high on / off ratio, especially the Br-2EPT device with only a few volts of VTH shift. The transfer characteristic curves of the three transistors were modulated by changing the gate voltage ( Fig.10 A, B, C), the interface modified transistors show lower on-current and higher top-current, respectively, and can maintain excellent gate induced current modulation (GCM) even at ultra-low gate voltage (-0.001V). Fig.10D, E, F).

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a perovskite thin film transistor based on a self-assembled monolayer, characterized in that: The following steps are involved: (1) spin coating a small molecule solution dissolved in an organic solvent on a silicon wafer coated with silicon dioxide, and annealing at 100-120° C. for 10-15 min to obtain a multilayer small molecule film, wherein the small molecule solution is Br-2EPO or Br-2EPT; and the concentration of the small molecule solution is 0.5-5 mg / mL; (2) Spin-coat the organic solvent onto the multi-layer small molecule film.

2. The method for preparing a perovskite thin film transistor based on a self-assembled monolayer according to claim 1, characterized in that: In step (1), the concentration of the small molecule solution is 1-3 mg / mL.

3. The method for preparing a perovskite thin film transistor based on a self-assembled monolayer according to claim 1, characterized in that: In step (1), the rotation speed during spin coating is 3000-4000 rpm, and the spin coating time is 25-30 s.

4. The method for preparing a perovskite thin film transistor based on a self-assembled monolayer according to claim 1, characterized in that: In step (1), the silicon wafer coated with the silicon dioxide layer is pretreated as follows: The silicon wafer coated with the silicon dioxide layer is cleaned in acetone, deionized water and isopropanol solvent respectively; then the cleaned silicon wafer is transferred to a thermal evaporation chamber to evaporate the electrode, and then UV treatment is performed.

5. The method for preparing a perovskite thin film transistor based on a self-assembled monolayer according to claim 1, characterized in that: In step (2), the rotation speed during spin coating is 4000-4500 rpm, and the spin coating time is 30-35 s.

6. The method for preparing a perovskite thin film transistor based on a self-assembled monolayer according to claim 1, characterized in that: The organic solvent includes at least one of ethanol and isopropanol.

7. The method for preparing a perovskite thin film transistor based on a self-assembled monolayer according to claim 1, characterized in that: In step (2), the amount of the organic solvent used is 100-500uL.

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