A circularly polarized light detector and a preparation method thereof

Abstract

The application discloses a circularly polarized light detector and a preparation method thereof, and belongs to the technical field of photoelectric detectors. The circularly polarized light detector comprises, from bottom to top, a substrate, a gate electrode, a conjugated polymer layer, a chiral supramolecular layer, a source electrode and a drain electrode. Thus, the integration degree can be greatly improved, and the overall volume can be reduced to below 10 cm3. The application is suitable for application fields, such as miniature endoscopes and wearable sensors, which have strict requirements on the size of devices, avoids the integration bottleneck caused by the combination of traditional optical elements, has excellent coupling effect on circularly polarized light through the chiral supramolecular layer, can accurately distinguish left-handed and right-handed circularly polarized light, and has a significantly higher asymmetric factor than an organic circularly polarized light detector based on a traditional chiral small molecule or polymer.

Description

TECHNICAL FIELD

[0001] The application relates to a circularly polarized light detector and a preparation method thereof, and belongs to the technical field of photoelectric detectors. BACKGROUND

[0002] Circularly polarized light becomes a key information carrier in the fields of biomedicine, quantum communication, remote sensing and the like due to the spiral propagation characteristic: in biomedicine, the chiral phospholipid molecules of cancer cell membranes produce a weak circularly polarized signal difference, and a detector needs to have a high asymmetry factor to realize early diagnosis; in quantum communication, the circular polarization state is used as a quantum bit carrier, and a detector needs to have a sub-second level of fast response capability to meet the demand of high-speed signal processing; in the field of remote sensing, the polarized reflection spectrum analysis of ground vegetation and atmospheric aerosols needs a detector to maintain long-term stability in the 400-1000nm wave band.

[0003] However, the traditional circular polarization detection system relies on a combination architecture of a polarizer, a quarter-wave plate and a silicon-based detector, and has defects such as contradiction between volume and integration, high cost, easy loss, low polarization distinction, and the like, and is difficult to meet the actual application demand. SUMMARY

[0004] To solve the above technical problems, the application provides a circularly polarized light detector and a preparation method thereof, which combines the advantages of the heterojunction formed by the chiral supramolecular layer and the conjugated polymer layer, and overcomes the problems of the traditional circularly polarized light detector in the prior art, such as large volume, low integration, low polarization distinction, low field effect mobility and slow response of the organic circular polarization detector.

[0005] The technical scheme adopted by the application to solve the technical problems is as follows:

[0006] A circularly polarized light detector sequentially comprises, from bottom to top, a substrate, a gate electrode, a conjugated polymer layer, a chiral supramolecular layer, a source electrode and a drain electrode, wherein:

[0007] The conjugated polymer layer is a p-type organic semiconductor thin film, the thickness is 50-200nm, and the field effect mobility is greater than or equal to 0.5cm² / (V.s).

[0008] The chiral supramolecular layer is a supramolecular co-assembly of chiral monomers and achiral monomers, the molar ratio of the chiral monomers to the achiral monomers is 1:10 to 1:50, the thickness of the chiral supramolecular layer is 80-200nm, and the circularly polarized luminescence asymmetry factor of the chiral supramolecular layer to circularly polarized light at a wavelength of 532nm is greater than or equal to 0.15.

[0009] Preferably, the thickness of the source electrode and the drain electrode is 70-90nm, the spacing is 50pm±5pm, and the contact resistance is less than or equal to 1kΩ.

[0010] Preferably, the substrate comprises a single crystal silicon wafer with a resistivity of 1-10 Ω·cm and a SiO2 insulating layer with a thickness of 300 nm±5 nm grown on the surface thereof by thermal oxidation; and the gate electrode is a single crystal silicon wafer with a Cr / Au composite electrode as the lead-out end.

[0011] Preferably, the material of the conjugated polymer layer is selected from one of poly-3-hexylthiophene (P3HT), diketopyrrolopyrrole and thiophene-thiophene-based polymer (DPP-TT), or indenocarbazole-dithiophene-thiophene and benzothiadiazole-based polymer (IDTT-BT); wherein the number average molecular weight of the P3HT is 5×10 4 to 1×10 5 ; the number average molecular weight of the DPP-TT is 8×10 4 ; and the number average molecular weight of the IDTT-BT is 1.2×10 5 .

[0012] Preferably, in the chiral supramolecular layer, the chiral monomer is (S)-2 or (R)-2, the achiral monomer is a compound containing a fluorene unit and a carboxyl group, and the molar ratio of the chiral monomer to the achiral monomer is 1:30.

[0013] Preferably, the chiral supramolecular layer is prepared from a mixed solvent of chlorobenzene and toluene, the volume ratio of chlorobenzene to toluene is 7:3, the purity of the solvent is ≥99.8%, and the water content is ≤10 ppm.

[0014] A method for preparing a circularly polarized light detector, comprising the following steps:

[0015] S1: providing and pretreating a substrate and a gate electrode;

[0016] S2: preparing a conjugated polymer layer on the substrate;

[0017] S3: preparing a chiral supramolecular layer on the conjugated polymer layer;

[0018] S4: preparing a source electrode and a drain electrode on the chiral supramolecular layer;

[0019] S5: packaging the device.

[0020] Preferably, the step S2 comprises:

[0021] vacuum drying the conjugated polymer powder at 80°C and 10 Pa for 12 hours;

[0022] dissolving the dried conjugated polymer in a chlorobenzene solvent to prepare a solution with a concentration of 5-15 mg / mL, and then forming a film by spin coating after stirring, ultrasonic treatment and filtration;

[0023] The thin film after spin coating is annealed at 80-150 DEG C for 20-30 minutes;

[0024] The parameters of the film formed by the spin coating method are as follows:

[0025] The solution is spread at 500 rpm for 5 seconds, and then the thickness is controlled by spin coating at 1000-5000 rpm for 30 seconds, wherein the spin coating speed of P3HT is 3000 rpm, the spin coating speed of DPP-TT is 4000 rpm, and the spin coating speed of IDTT-BT is 3500 rpm.

[0026] Preferably, the step S3 comprises:

[0027] The chiral monomer and the achiral monomer are weighed in a molar ratio of 1:10 to 1:50, dissolved in a chlorobenzene / toluene mixed solvent, and co-assembled by stirring at 50 DEG C for 4 hours;

[0028] The co-assembled solution is deposited into a film by a spin coating method at a spin coating speed of 800-1500 rpm;

[0029] The thin film after spin coating is annealed at 80 DEG C for 2 hours.

[0030] Preferably, the step S4 comprises:

[0031] An electrode pattern is defined by using a mask alignment technology, and the alignment deviation between the electrode and the chiral supramolecular layer is ensured to be less than or equal to 5 microns.

[0032] The metal electrode is evaporated at a rate of 0.1-0.3 nm / s under the condition that the vacuum degree is less than or equal to 1*10 -5 Pa.

[0033] Compared with the prior art, the present application has the beneficial effects that:

[0034] By introducing a heterojunction composed of a chiral supramolecular layer and a conjugated polymer layer, high-precision discrimination of left-handed and right-handed circularly polarized light is realized, the asymmetric factor is significantly improved, and the problem of low polarization discrimination of traditional detectors is solved.

[0035] The device structure is highly integrated, and the overall volume is significantly reduced, which is suitable for application scenarios such as micro endoscopes, wearable devices, and other space-demanding application scenarios.

[0036] The high selectivity of chiral supramolecules and the high mobility of conjugated polymers are combined, so that the detector not only has excellent circular polarization recognition ability, but also has good electrical performance and fast response speed, and the comprehensive performance is superior. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor based on the drawings shown.

[0038] Figure 1 A schematic diagram of a partial structure of a device of the present application;

[0039] Figure 2 A structural formula diagram of an achiral monomer of the present application;

[0040] Figure 3 A structural formula diagram of a chiral monomer (S)-2 in the present application;

[0041] Figure 4 A structural formula diagram of a chiral monomer (R)-2 in the present application;

[0042] Figure 5 A leakage source current-gate source voltage curve diagram of the present application under irradiation of dark state, left circularly polarized light and right circularly polarized light;

[0043] Figure 6 A leakage source current-time curve diagram of the present application under irradiation of circularly polarized light.

[0044] In the figure: 1, substrate; 2, gate electrode; 3, conjugated polymer layer; 4, chiral supramolecular layer; 5, source electrode; 6, drain electrode. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0046] Embodiment 1

[0047] This embodiment provides a circularly polarized light detector, the structure of which is shown in Figure 1 from bottom to top, sequentially including a substrate 1, a gate electrode 2, a conjugated polymer layer 3, a chiral supramolecular layer 4, a source electrode 5 and a drain electrode 6.

[0048] Preparation of the substrate 1 and the gate electrode 2:

[0049] A single crystal silicon wafer with crystal orientation (100) and resistivity of 5 Ω-cm is selected as the conductive part of the substrate 1. The wafer is placed in a thermal oxidation furnace to grow a 300 nm thick silicon dioxide (SiO2) layer as the insulating layer under the atmosphere of oxygen at 1100 °C. The main body of the gate electrode 2 is the single crystal silicon wafer itself. On the edge of the wafer, a 10 nm thick chromium (Cr) and a 40 nm thick gold (Au) are sequentially evaporated by the electron beam evaporation method to form a Cr / Au composite lead electrode with a contact resistance of ≤50 Ω.

[0050] Preparation of the conjugated polymer layer 3:

[0051] A poly-3-hexylthiophene (P3HT) with regio-regularity ≥98% and number average molecular weight of about 8 x 104 4 is selected as the p-type organic semiconductor material. First, the P3HT powder is vacuum dried at 80 °C and 10 Pa for 12 hours to remove moisture. Then, the dried P3HT is dissolved in chlorobenzene to prepare a solution with a concentration of 10 mg / mL, which is stirred in a 60 °C oil bath for 2 hours until completely dissolved. After ultrasonic treatment and filtration through a 0.2 μm polytetrafluoroethylene filter membrane, the solution is formed into a film on the pretreated SiO2 / Si substrate 1 by spin coating. The spin coating parameters are: first spin at 500 rpm for 5 seconds to spread the solution, and then spin at 3000 rpm for 30 seconds. The spin-coated film is immediately transferred to a heating stage and annealed at 120 °C under a nitrogen atmosphere for 30 minutes. Finally, a P3HT conjugated polymer layer 3 with a thickness of about 80 nm, a smooth surface, and good crystallinity is obtained, and its field-effect mobility is tested to be ≥0.5 cm2 / (V-s).

[0052] Preparation of the chiral supramolecular layer 4:

[0053] The chiral supramolecular layer 4 of this embodiment is formed by supramolecular co-assembly of a chiral monomer (S)-2 and an achiral monomer, wherein the structural formula of the achiral monomer is shown in Figure 2 , and the structural formula of the chiral monomer (S)-2 is shown in Figure 3 . The two monomers are accurately weighed in a molar ratio of 1:30. The weighed monomers are dissolved in a mixed solvent of chlorobenzene and toluene, and magnetically stirred at 50 °C for 4 hours for sufficient supramolecular co-assembly to form a uniform and stable solution. The co-assembly solution is spin-coated on the above-mentioned P3HT conjugated polymer layer 3 at a spin speed of 1500 rpm for 30 seconds. Then, the film is annealed at 80 °C for 2 hours to remove residual solvent and stabilize the supramolecular structure, and finally a chiral supramolecular layer 4 with a thickness of about 80 nm is formed. The circularly polarized luminescence asymmetry factor of this layer for circularly polarized light at a wavelength of 532 nm is ≥0.15.

[0054] Preparation of the source electrode 5 and the drain electrode 6:

[0055] ​A high-precision metal mask is used to precisely align the device substrate with the completed chiral supramolecular layer 4, ensuring that the alignment deviation between the electrode pattern and the functional layer is ≤5 μm. The substrate is placed in a high-vacuum evaporation chamber, and gold (Au) is evaporated at a rate of 0.2 nm / s under a vacuum degree of ≤1×10 -5

[0056] The circularly polarized light detector prepared in this example is subjected to performance testing. Under the irradiation of circularly polarized light with a wavelength of 532 nm and a power density of 10 mW / cm², the output characteristics of the device are measured. As shown in FIG. 2, the drain-source current (IDS) generated under the irradiation of left-circularly polarized light (L-CPL) is significantly higher than that under the irradiation of right-circularly polarized light (R-CPL), and the dark-state current is extremely low, indicating that the device has excellent polarization discrimination and switching ratio. The asymmetry factor calculated from the photocurrent data can reach 0.18. The field-effect mobility of the device is calculated to be about 0.62 cm² / (V·s), and the response time is about 0.42 seconds. These performance indicators are significantly better than those of detectors relying on the combination of traditional optical elements, and also solve the problem of poor carrier transport performance of pure chiral organic semiconductors. Figure 5

[0057] As shown in FIG. 3, when the laser is turned on, the photocurrent of the device rapidly rises to a peak value within about 0.42 seconds; when the laser is turned off, the photocurrent returns to the dark-state level within about 0.35 seconds. This fast response characteristic proves that the detector of the present application not only has high polarization sensitivity, but also has good dynamic detection capability, which can meet the needs of real-time monitoring and high-speed communication and other application scenarios. Figure 6

[0058] Comparative Example 1

[0059] The preparation of the circularly polarized light detector with a blended structure is the same as that of Example 1, except that the preparation method of the chiral recognition layer. The chiral monomer (S)-2 and P3HT are co-dissolved in chlorobenzene at a mass ratio of 1:20, and after spin-coating into a film, annealing at 100°C for 10 minutes to form a blended active layer.

[0060] Example 2

[0061] This example aims to illustrate the influence of using different conjugated polymer materials and optimizing the proportion of chiral components on the comprehensive performance of the detector.

[0062] Substrate 1 and gate electrode 2: the preparation process is the same as that of Example 1.

[0063] ​​​Conjugated polymer layer 3: A diketopyrrolopyrrole and thienothiophene based polymer (DPP-TT) was selected and formulated into a 10 mg / mL solution in chlorobenzene, spin-coated onto substrate 1 at 4000 rpm to form a film, followed by annealing at 150℃ for 20 minutes to form a thin film with a thickness of about 100 nm.

[0064] Chiral supramolecular layer 4: To explore the optimal ratio, co-assembly solutions with molar ratios of chiral monomer (R)-2 to achiral monomer of 1:20, 1:30 and 1:40 were prepared, respectively. The structure of (R)-2 is shown in the following formula: Figure 4 The three solutions were spin-coated (1200 rpm) on the DPP-TT layer and annealed at 80℃ for 2 hours to form a chiral supramolecular layer 4 with a thickness of about 120 nm.

[0065] Source electrode 5 and drain electrode 6: The preparation process is the same as in Example 1.

[0066] Performance comparison and analysis:

[0067] Molar ratio 1:20: The chiral recognition ability is the strongest, and the measured asymmetric factor is about 0.19, but the higher chiral component may slightly affect the interface charge transport, and the field effect mobility is about 0.48 cm² / (V·s).

[0068] Molar ratio 1:30: The best balance between polarization recognition and electrical performance is achieved, with an asymmetric factor of about 0.18 and an improved field effect mobility of 0.55 cm² / (V·s), and the film uniformity is the best.

[0069] Molar ratio 1:40: The chiral recognition ability decreases slightly, but the charge transport is more smooth.

[0070] This example demonstrates that the ratio of 1:30 in the molar ratio range of 1:10 to 1:50 can achieve a synergistic optimization of high performance, which is different from the existing technology that tries to balance performance through complex heterogeneous structures. The present application can achieve this through simple supramolecular co-assembly ratio control.

[0071] Example 3:

[0072] This example emphasizes the selectivity of conjugated polymer materials and the key role of the purity of the solvent used to prepare the chiral supramolecular layer in the stability of the device performance.

[0073] Substrate 1 and gate electrode 2: The preparation process is the same as in Example 1.

[0074] Conjugated polymer layer 3: Select the polymer based on indenodithienothiophene and benzothiadiazole (IDTT-BT), prepare a solution with a concentration of 12 mg / mL with chlorobenzene, filter and spin-coat a film at a speed of 3500 rpm, and anneal at 140°C for 25 minutes to form a film with a thickness of about 150 nm.

[0075] Chiral supramolecular layer 4: In this embodiment, the quality of the solvent is strictly controlled. Analytically pure chlorobenzene and toluene with a purity of ≥99.8% and a water content of ≤10 ppm are used, and are strictly mixed in a volume ratio of 7:3. (S)-2 and the achiral monomer are weighed in a molar ratio of 1:30, dissolved in the above-mentioned high-purity mixed solvent, and stirred at 50°C for 4 hours for co-assembly. Then spin-coat on the IDTT-BT layer at a speed of 1000 rpm, and anneal at 80°C for 2 hours to form a high-quality chiral supramolecular layer 4 with a thickness of about 180 nm.

[0076] Source electrode 5 and drain electrode 6: The preparation process is the same as in Example 1.

[0077] Performance and stability: The obtained device has an asymmetry factor of about 0.17 under CPL irradiation at 532 nm, and a field effect mobility of about 0.58 cm² / (V·s). Due to the wide absorption characteristics of IDTT-BT, the device shows good polarization response in the visible light band. Through comparative experiments, it is found that if ordinary solvents with high water content are used, the film quality of the chiral supramolecular layer 4 will decrease significantly, pinholes will appear, the asymmetry factor will decrease by more than 30%, and the performance of the device will decay faster in a humid and hot environment. This embodiment proves that the limited solvent purity parameter is crucial to ensure the repeatability and long-term stability of the device performance.

[0078] Comparison of key performance parameters between Example 1 and Comparative Example 1, as shown in Table 1 below:

[0079]

[0080] Influence of solvent purity on long-term stability of the device, as shown in Table 2 below:

[0081]

[0082] According to the analysis, the data in Table 1 clearly shows that Example 1 is significantly superior to Comparative Example 1 in core indicators such as mobility, g-factor, and response speed. This result confirms that the functional decoupling design effectively solves the inherent contradiction between the poor carrier transport of chiral materials and the weak chiral recognition of conjugated polymers, which is not expected by those skilled in the art.

[0083] The molar ratio of 1:30 in Example 1 is the best window for balancing supramolecular ordered assembly and charge transport;

[0084] The purity of the solvent in Table 2 is ≥ 99.99%, which is a necessary condition to ensure long-term stability of the device, and trace amounts of water can cause destruction of the supramolecular structure and interface defects.

[0085] Example 2 demonstrates that the technical scheme of the present application is applicable to various high-mobility conjugated polymer systems (P3HT, DPP-TT, IDTT-BT), and can achieve the synergistic optimization of mobility ≥ 0.5 cm² / (V·s) and g ≥ 0.15, which embodies the scalability of the scheme.

[0086] Although embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A circularly polarized light detector, characterized by, From bottom to top, it includes substrate (1), gate electrode (2), conjugated polymer layer (3), chiral supramolecular layer (4), source electrode (5) and drain electrode (6), wherein: The conjugated polymer layer (3) is a p-type organic semiconductor thin film, the thickness is 50-200nm, and the field effect mobility is ≥0.5cm² / (V·s); The chiral supramolecular layer (4) is a supramolecular co-assembly of chiral monomers and achiral monomers, the molar ratio of the chiral monomers to the achiral monomers is 1:10 to 1:50, and the thickness of the chiral supramolecular layer (4) is 80-200nm, and the circularly polarized luminescence asymmetry factor thereof at 532nm wavelength is ≥0.15; In the chiral supramolecular layer (4), the chiral monomer is (S)-2 or (R)-2, the achiral monomer is a compound containing a fluorene unit and a carboxyl group, and the molar ratio of the chiral monomer to the achiral monomer is 1:30; The material of the conjugated polymer layer (3) is selected from one of poly-3-hexylthiophene (P3HT), diketopyrrolopyrrole and thienothiophene based polymer (DPP-TT) or indenodithienothiophene and benzothiadiazole based polymer (IDTT-BT); wherein the number average molecular weight of the P3HT is 5x10 4 to 1x10 5 , the regioregularity is ≥98%; the number average molecular weight of the DPP-TT is 8x10 4 ; the number average molecular weight of the IDTT-BT is 1.2x10 5 .

2. The circularly polarized light detector according to claim 1, characterized in that The thickness of the source electrode (5) and the drain electrode (6) is 70-90nm, the spacing is 50μm±5μm, and the contact resistance is ≤1kΩ.

3. The circular polarization photodetector according to claim 1, wherein The substrate (1) includes a single crystal silicon wafer and a SiO2 insulating layer grown on the surface thereof by thermal oxidation, the resistivity of the single crystal silicon wafer is 1-10Ω·cm, and the thickness of the SiO2 insulating layer is 300nm±5nm; the gate electrode (2) is mainly a single crystal silicon wafer, and the lead-out end thereof is a Cr / Au composite electrode.

4. The circular polarization photodetector according to claim 1, wherein, The chiral supramolecular layer (4) is prepared from a mixed solvent of chlorobenzene and toluene, the volume ratio of chlorobenzene to toluene is 7:3, the purity of the solvent is ≥99.8%, and the water content is ≤10ppm.

5. A method of manufacturing a circularly polarized light detector as claimed in any one of the claims 1-4, characterized in that, It includes the following steps: S1: providing and pretreating the substrate (1) and the gate electrode (2); S2: preparing the conjugated polymer layer (3) on the substrate (1); S3: preparing the chiral supramolecular layer (4) on the conjugated polymer layer (3); S4: preparing the source electrode (5) and the drain electrode (6) on the chiral supramolecular layer (4); S5: packaging the device.

6. The method of claim 5, wherein the method further comprises: The step S2 includes: Vacuum drying the conjugated polymer powder at 80℃, 10Pa for 12 hours; Dissolving the dried conjugated polymer in chlorobenzene solvent to prepare a solution with a concentration of 5-15mg / mL, and then stirring, ultrasonicating and filtering to form a film by spin coating method; Annealing the film after spin coating, the annealing temperature is 80-150℃, and the annealing time is 20-30 minutes; The parameters of the spin coating method for film formation are as follows: Firstly, spin coating at 500rpm for 5 seconds to spread the solution, and then spin coating at a speed of 1000-5000rpm for 30 seconds to control the thickness, wherein the spin coating speed of P3HT is 3000rpm, the spin coating speed of DPP-TT is 4000rpm, and the spin coating speed of IDTT-BT is 3500rpm.

7. The method for fabricating a circularly polarized optical detector according to claim 5, characterized in that, The step S3 includes: Dissolving the chiral monomer and the achiral monomer in a chlorobenzene / toluene mixed solvent at a molar ratio of 1:10 to 1:50, and co-assembling by stirring at 50℃ for 4 hours; Depositing the co-assembled solution into a film by spin coating method at a spin coating speed of 800-1500rpm; The thin film after spin coating is annealed at 80°C for 2 hours.

8. The method of claim 5, wherein the method further comprises: The step S4 comprises: The electrode pattern is defined using a mask alignment technique, ensuring that the alignment deviation of the electrode and the chiral supramolecular layer is ≤ 5 μm; The metal electrode was evaporated at a rate of 0.1-0.3 nm / s under a vacuum of ≤ 1 x 10 -5 Pa.

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