A three-narrow-wavelength organic photodetector based on a back-side filter structure and its fabrication method

Abstract

This invention provides a three-narrow-wavelength organic photodetector based on a back-side filter structure and its fabrication method, belonging to the field of organic photodetector technology. This organic photodetector fabricates an organic filter layer on the outside of the incident substrate. By selecting a filter layer material that matches the response band of the photosensitive layer and adjusting the composition, ratio, and film thickness of the filter layer, three-narrow-wavelength detection of specific wavelength bands can be achieved. The three-narrow-wavelength organic photodetector designed in this invention exhibits selective responses simultaneously in three wavelength bands: ultraviolet 340nm, green light 540nm, and red light 760nm. The EQE corresponding to each wavelength band can reach 5%, 20%, and 15%, respectively, and the FWHM is approximately 60nm, 40nm, and 40nm, respectively. This three-narrow-wavelength photodetector has been verified to be applicable to fields such as encrypted optical communication and feature target recognition. Furthermore, the device structure of this invention is simple, and the fabrication process is convenient.

Description

Technical Field

[0001] This invention belongs to the field of organic photodetector technology, specifically relating to a three-narrow-wavelength organic photodetector based on a back-side filter structure and its fabrication method. Background Technology

[0002] Narrow-band photodetectors are photodetectors that exhibit selective response characteristics to a specific narrow wavelength band—that is, a wavelength band with a peak half-width (FWHM) of less than 100 nm. Compared to traditional wide-band photodetectors, these detectors possess refined spectral recognition capabilities and have broad application prospects in fields such as national defense, encrypted optical communication, specific gas detection, and biological monitoring in specific wavelength bands. With the development of the information age, special applications such as multispectral detection and multi-band feature target recognition are constantly evolving. Due to their rich feature information capture capabilities, multi-narrow-band photodetectors demonstrate more significant advantages in areas such as target recognition in complex backgrounds and complex encrypted optical communication. Therefore, industrial transformation and upgrading, as well as information technology development, have placed demands on the research of multi-narrow-band photodetectors.

[0003] Traditional narrow-band photodetectors often rely on adding external optical elements (such as gratings, beam splitters, filters, or micro-surface structures) to wide-band inorganic photodetectors. These methods undoubtedly limit the miniaturization, portability, and integration of the detection system. In the field of organic photodetectors, charge collection narrowing (Nat. Commun., 2015, 6, 6343.), charge injection narrowing (Adv. Opt. Mater., 2018, 6, 1800249.), and self-filtering narrowing (ACS Appl. Mater. Interfaces, 2020, 12, 13061–13067.) have been used to realize single-narrow-wavelength organic photodetectors. However, multi-narrow-wavelength photodetectors either rely on the complex structure, difficult fabrication, and complex subsequent readout circuits and algorithms of external microcavity array structure design (Adv. Mater., 2017, 29, 1702184.), or on the design of rare organic materials with multi-band absorption characteristics.

[0004] Therefore, it is of great significance to design a detector with multiple narrow-wavelength photoelectric detection capabilities on a simple structural unit detector. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention aims to provide a three-narrow-wavelength organic photodetector based on a back-side filter structure and its fabrication method. This organic photodetector has an organic filter layer fabricated on the outside of the incident substrate. By selecting a filter layer material that matches the response band of the photosensitive layer and adjusting the composition, ratio, and thickness of the filter layer, three-narrow-wavelength detection of a specific band can be achieved. The device structure of this invention is simple, and the fabrication process is convenient.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A three-narrow-wavelength organic photodetector based on a back-side filter structure comprises, from bottom to top, an organic filter layer, a transparent substrate, a first transparent conductive electrode, a first modification layer, a photosensitive layer, a second modification layer, and a second transparent conductive electrode;

[0008] The photosensitive layer is a bulk heterojunction with a wide-band response;

[0009] The absorption start wavelength of the absorption spectrum of the filter layer material should be greater than the start value of the response band of the photosensitive layer material to achieve a narrow-band response at the start of the response; the absorption end wavelength of the absorption spectrum of the filter layer material should be less than the end value of the response band of the photosensitive layer material to achieve a narrow-band response at the end of the response band of the photosensitive layer; and the absorption valley in the absorption spectrum of the filter layer material should correspond to the middle band of the three response bands of the three narrow-band organic photodetector.

[0010] Furthermore, the width of the absorption valley in the absorption spectrum of the filter layer material, combined with the thickness of the filter layer, makes the response band in the middle of the three narrow-wavelength organic photodetector narrower, preferably below 100nm; the lower the absorption coefficient of the absorption valley, the better.

[0011] Furthermore, the organic donor of the photosensitive layer is PBDB-T, the organic acceptor is ITIC-Th, and the response wavelength range of the bulk heterojunction is 300nm-800nm.

[0012] Furthermore, the three-narrow-wavelength organic photodetector has an inversion device structure, with the first transparent conductive electrode serving as the cathode, preferably made of ITO, PEDOT:PSS, graphene, or silver nanowires; the first modification layer is preferably made of PEIE, ZnO, LiF, PFN-Br, BCP, or C. 60 The second modification layer is preferably made of PEDOT:PSS, MoO3, NPB, PVK or NiO; the second transparent conductive electrode is the anode, and its preparation material is preferably Ag, Al or Au.

[0013] Furthermore, the filter layer is preferably a mixed membrane layer of F8T2 donor and ITIC-Th acceptor, with a membrane thickness of 200nm-500nm and a donor-to-acceptor mass ratio of (4-7):10.

[0014] Furthermore, the center wavelengths of the response bands of the three narrow-wavelength organic photodetector of the present invention are 340nm, 540nm, and 760nm;

[0015] F8T2 exhibits weak absorption at 340nm, while the absorption tail of ITIC-Th shows a slight blue shift relative to the tail of the response band of the photosensitive layer. The hybrid film of F8T2 and ITIC-Th has an absorption valley near 540nm. Based on these characteristics, three narrow-wavelength responses near 340nm, 540nm, and 760nm can be achieved.

[0016] A method for fabricating a three-narrow-wavelength organic photodetector based on a back-side filter structure includes the following steps:

[0017] Step 1. Clean the transparent substrate, dry it, and then perform ultraviolet ozone cleaning;

[0018] Step 2. A first transparent conductive electrode is fabricated on the front side of the cleaned transparent substrate using a deposition method;

[0019] Step 3. A first modification layer is prepared on the surface of the first transparent conductive electrode by spin coating, and then thermally annealed in an air atmosphere after spin coating;

[0020] Step 4. Preparation of photosensitive layer solution: The first donor material and the first acceptor material are placed in the first organic solvent, and then the solution is stirred and mixed at a certain temperature. After stirring, the photosensitive layer solution is obtained.

[0021] Step 5. In a nitrogen atmosphere, a photosensitive layer solution is spin-coated onto the surface of the first transparent conductive electrode using a spin-coating process. After spin-coating, a thermal annealing treatment is performed to obtain the photosensitive layer.

[0022] Step 6. Prepare a second modification layer on the surface of the photosensitive layer using a vacuum evaporation method;

[0023] Step 7. Prepare a second transparent conductive electrode on the surface of the second modified layer by vapor deposition;

[0024] Step 8. Preparation of filter layer solution: Place the second donor material and the second acceptor material into the second organic solvent, and then stir and mix the solution at a certain temperature. After stirring, the filter layer solution can be obtained.

[0025] Step 9. In a nitrogen atmosphere, a filter layer is prepared on the back side of a transparent substrate using spin coating. After completion, the desired three-narrow-wavelength organic photodetector can be obtained.

[0026] Furthermore, the absorption end wavelength of the second receptor absorption spectrum is slightly smaller than the end wavelength of the response band of the photosensitive layer.

[0027] Furthermore, in addition to spin coating, the preparation methods of the filter layer, the first cathode modification layer, the second cathode modification layer and the photosensitive layer can also be replaced by spin coating, blade coating, drop coating or spray coating.

[0028] Furthermore, if the filter layer is prepared by spin coating, with a spin coating speed of 300-700 rpm, the corresponding film thickness is approximately 230 nm-460 nm.

[0029] Furthermore, the filter layer material of the three narrow-wavelength photodetector is a hybrid film of F8T2 and ITIC-Th, and the process of its optimal performance device is as follows: the filter layer solution concentration is 34 mg / ml, the donor-acceptor ratio is 5:10, and the spin coating speed is 700 rpm (corresponding to a film thickness of approximately 230 nm).

[0030] The mechanism of this invention is as follows: A filter layer with a specific matching characteristic between its absorption spectrum and the response band of the photosensitive layer is prepared on the back side of the incident substrate of the organic photodetector to achieve three narrow-band organic photodetection. Specifically, the weak absorption band of the filter layer should correspond to the three narrow-band to be achieved and cover the response range of the photosensitive layer; more specifically, the absorption start wavelength of the filter layer should be slightly larger than the response start wavelength of the photosensitive layer, the absorption end wavelength should be slightly smaller than the response end wavelength of the photosensitive layer, and the wavelength at the absorption valley should correspond to the third narrow band, while satisfying the characteristics of sufficiently low absorption coefficient and sufficiently narrow absorption valley. By selecting a suitable filter layer material and adjusting the film thickness of the filter layer, flexible adjustment of the narrow-band response of the device can be achieved.

[0031] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0032] (1) This invention innovatively proposes to adjust the response band of the device by adjusting the weak absorption band of the filter layer, that is, by controlling the absorption start wavelength, absorption end wavelength and absorption valley of the filter layer. The three narrow-wavelength organic photodetector designed in this invention has selective response in three bands: ultraviolet 340nm, green light 540nm and red light 760nm. The EQE corresponding to each band can reach 5%, 20% and 15% respectively, and the FWHM is about 60nm, 40nm and 40nm respectively. This three narrow-wavelength photodetector has been verified to be applicable to fields such as encrypted optical communication and feature target recognition.

[0033] (2) The preparation process of this invention is simple and has good compatibility, and it can be widely used in the field of organic narrow-wavelength photodetectors. Attached Figure Description

[0034] Figure 1This is a schematic diagram of the organic photodetector based on a back-side filter structure in this invention.

[0035] Figure 2 This is the normalized absorption spectrum of the photosensitive layer and filter layer materials used in Embodiment 1 of the present invention;

[0036] Figure (a) shows the absorption spectra of the three organic materials used in the device, and Figure (b) shows the absorption spectrum of the filter layer F8T2:ITIC-Th.

[0037] Figure 3 The image shows the EQE response spectrum of the three narrow-wavelength organic photodetector prepared in Example 1.

[0038] Figure 4 The image shows the JV curve of the three narrow-wavelength organic photodetector prepared in Example 1.

[0039] Figure 5 The EQE response spectra of the three narrow-wavelength organic photodetectors prepared in Examples 1 and 2 are shown.

[0040] Figure (a) shows the EQE response of the filter layer at different spin coating speeds with the same ratio, and Figure (b) shows the EQE response of the filter layer at different ratios with the same spin coating speed.

[0041] Figure 6 The EQE response spectrum of the three narrow-wavelength organic photodetector prepared for Comparative Example 1 is shown. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0043] A three-narrow-wavelength organic photodetector based on a back-side filter structure is shown in the schematic diagram below. Figure 1 As shown, from bottom to top, the layers are: organic filter layer, transparent substrate, first transparent conductive electrode (ITO), first modification layer (ZnO), photosensitive layer (PBDB-T:ITIC-Th), second modification layer (MoO3), and second transparent conductive electrode (Ag).

[0044] The photosensitive layer is a bulk heterojunction layer with a wide-band response, prepared by organic donor and organic acceptor.

[0045] The starting value of the absorption peak of the filter layer material should be less than the starting value of the response of the photosensitive layer material to achieve a narrow band response at the beginning of absorption (the absorption start of the filter layer material is slightly red-shifted relative to the response start band of the photosensitive layer material); the ending value of the absorption peak of the filter layer material should be greater than the response start value of the photosensitive layer material to achieve a narrow band response at the end of the absorption peak; and the absorption valley of the filter layer material should correspond to the middle band of the three narrow bands.

[0046] Example 1

[0047] A method for fabricating a three-narrow-wavelength organic photodetector based on a back-side filter structure includes the following steps:

[0048] Step 1. The transparent substrate with ITO deposited on one side is ultrasonically cleaned sequentially with detergent, deionized water, acetone and isopropanol. After being dried with nitrogen, it is treated with ultraviolet ozone for 20 minutes to obtain a transparent substrate with the first transparent conductive electrode ITO deposited on it.

[0049] Step 2. The first modified layer ZnO is prepared on the surface of the first transparent conductive electrode ITO by spin coating. The ZnO precursor solution is prepared on the ITO cathode by spin coating. The spin coating speed and time are 4000 rpm and 40s, respectively. The heat annealing treatment is carried out in an air atmosphere. The heat annealing temperature and time are 200℃ and 30min, respectively.

[0050] Step 3. Preparation of photosensitive layer solution: PBDB-T is used as the donor material of the photosensitive layer, and ITIC-Th is used as the acceptor material of the photosensitive layer, with a mass ratio of 1:1. Chlorobenzene is used as the organic solvent to prepare the photosensitive layer solution, and the total mass concentration of donor and acceptor is 30 mg / ml. The solution is placed on a heated stirring table at 55°C and stirred for more than 12 hours to obtain the photosensitive layer solution.

[0051] Step 4. In a nitrogen atmosphere, a photosensitive layer solution is spin-coated onto the surface of the ZnO electrode using a spin-coating process. The spin-coating speed and time are 2000 rpm and 40 s, respectively. After spin-coating, the solution is heat-annealed at 110℃ for 10 min to obtain the photosensitive layer PBDB-T:ITIC-Th.

[0052] Step 5. Prepare a second modification layer of MoO3 on the surface of the photosensitive layer PBDB-T:ITIC-Th using vacuum evaporation, with a evaporation pressure of 1×10⁻⁶. -4 Pa, the thickness of the second modification layer is 10 nm;

[0053] Step 6. A second transparent conductive electrode Ag is prepared on the surface of the second modified layer MoO3 by vapor deposition at a vapor deposition pressure of 10. -4 Pa, with a thickness of 100 nm;

[0054] Step 7. Preparation of filter layer solution: Using F8T2 as the donor material and ITIC-Th as the acceptor material at a mass ratio of 5:10, and chlorobenzene as the organic solvent, a filter layer solution is prepared with a total concentration of 34 mg / ml; then the solution is placed on a heated stirring table at 55°C and stirred for more than 12 hours. After stirring, the filter layer solution is obtained.

[0055] Step 8. In a nitrogen atmosphere, a filter layer is prepared on the other side of the transparent substrate by spin coating. The spin coating speed and time are 700 rpm and 60 s, respectively. After completion, the desired three-narrow-wavelength organic photodetector can be obtained.

[0056] Figure 2 The normalized absorption spectra of the photosensitive layer and filter layer materials used in Embodiment 1 of the present invention are shown. Specifically, Figure (a) shows the absorption spectra of the three organic materials used in the device, and Figure (b) shows the absorption spectrum of the filter layer F8T2:ITIC-Th. As a photosensitive layer material, PBDB-T:ITIC-Th has an absorption spectrum ranging from 300 nm to 800 nm. As filter layer materials, F8T2 has an absorption spectrum ranging from 300 nm to 520 nm, and ITIC-Th has an absorption spectrum ranging from 540 nm to 800 nm. The mixed filter film F8T2:ITIC-Th exhibits the weakest absorption before 340 nm, near 540 nm, and after 760 nm.

[0057] Figure 3 The image shows the EQE response spectrum of the three narrow-wavelength organic photodetector prepared in Example 1. Its response spectrum has narrow-wavelength responses in three bands: 340nm, 540nm and 760nm, with FWHM values ​​of 60nm, 40nm and 40nm, respectively.

[0058] Figure 4 The JV curves for the three narrow-wavelength organic photodetector prepared in Example 1 are shown, including the dark current density, photocurrent density at 340 nm, photocurrent density at 540 nm, and photocurrent density at 760 nm. Performance characterization results are as follows: Under standard test conditions, with an applied bias voltage of -0.5V, the measured dark current density is 1.36 × 10⁻⁶. - 8 A / cm 2 At 340nm in the ultraviolet light (0.145mW / cm²), 2 ), green light 540nm (0.574mW / cm) 2 ), Red light 760nm (0.417mW / cm) 2 The photocurrent density in the three bands is 3.44 × 10⁻⁶. -5 A / cm 2 5.02×10-5 cm 2 3.34×10 -6 / cm 2 The EQE values ​​were 5%, 20%, and 15%, respectively, and the FWHM values ​​were 60nm, 40nm, and 40nm, respectively.

[0059] Example 2

[0060] Prepare a three-narrow-wavelength organic photodetector according to the steps of Example 1, only adjusting the spin coating speed in step 8 to 400, 500 and 600 rpm to adjust the thickness of the filter layer; or only adjusting the mass ratio of donor material to acceptor material in step 7 to 6:10 and 7:10, while keeping other steps unchanged.

[0061] Comparative Example 1

[0062] The three narrow-wavelength organic photodetector was prepared according to the steps of Example 1, except that the mass ratio of F8T2 and ITIC-Th in step 7 was adjusted to 7:10, and the spin coating speed and time in step 8 were 1000 rpm and 60 s, respectively, while the other steps remained unchanged.

[0063] The modulation process EQE response spectra of the three narrow-wavelength organic photodetectors prepared in Examples 1, 2, and 1 are shown below. Figure 5 and Figure 6 As shown, it can be concluded that by adjusting the spin coating speed of the filter layer, the thickness of the filter layer can be adjusted, thereby achieving the adjustment of the device's response wavelength.

[0064] Adjusting the filter layer thickness not only affects the peak EQE of organic photodetectors but also the full width at half maximum (FWHM) of the device's response peak. Specifically, at the same ratio, as the filter layer thickness increases, the EQE at 340 nm gradually decreases to near zero, and the FWHM shrinks. The responses at 540 nm and 760 nm also gradually decrease. Different donor-acceptor mass ratios primarily affect the peak FWHM; as the proportion of F8T2 increases, the peak FWHM at 340 nm and 540 nm decreases. In other words, adjusting the ratio mainly affects the EQE ratio and the peak FWHM at different peak values. At the same concentration and spin-coating speed, as the proportion of F8T2 donor increases, the filter layer thickness increases, thus decreasing the overall EQE of the device. Simultaneously, due to the increased donor proportion, the ratio of transmittance before 540 nm to transmittance after 540 nm decreases. This is reflected in the EQE spectrum of the three narrow-wavelength optical detectors, namely: overall, the response at each peak is reduced, and the ratio of the peak EQE at 340nm and 540nm to the peak EQE at 760nm decreases. At the same time, it shows that the FWHM before 540nm is narrower and the FWHM after 540nm is wider.

[0065] Therefore, when designing a three-narrow-wavelength photodetector with a back-side filter structure, it is necessary to weigh the material, thickness, EQE, and HWHM of the filter layer according to the specific application requirements.

[0066] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A three-narrow-wavelength organic photodetector based on a back-side filter structure, characterized in that, From bottom to top, the layers are: an organic filter layer, a transparent substrate, a first transparent conductive electrode, a first modification layer, a photosensitive layer, a second modification layer, and a second transparent conductive electrode. The photosensitive layer is a bulk heterojunction with a wide-band response; The absorption start wavelength of the absorption spectrum of the filter layer material should be greater than the start value of the response band of the photosensitive layer material to achieve a narrow-band response at the start of the response; the absorption end wavelength of the absorption spectrum of the filter layer material should be less than the end value of the response band of the photosensitive layer material to achieve a narrow-band response at the end of the response band of the photosensitive layer; and the absorption valley in the absorption spectrum of the filter layer material should correspond to the middle band of the three response bands of the three narrow-band organic photodetector. The width of the absorption valley in the absorption spectrum of the filter layer material, combined with the thickness of the filter layer, ensures that the response band in the middle of the three narrow-wavelength organic photodetector is below 100nm; the lower the absorption coefficient of the absorption valley, the better. The center wavelengths of the response bands of the three narrow-wavelength organic photodetectors are 340nm, 540nm, and 760nm.

2. The three-narrow-wavelength organic photodetector as described in claim 1, characterized in that, The organic donor of the photosensitive layer is PBDB-T, the organic acceptor is ITIC-Th, and the response wavelength range of the bulk heterojunction is 300nm-800nm.

3. The three narrow-wavelength organic photodetector as described in claim 1, characterized in that, The three narrow-wavelength organic photodetector has an inversion device structure. The first transparent conductive electrode is the cathode, and its material is ITO, PEDOT:PSS, graphene, or silver nanowires. The first modification layer is prepared from materials such as PEIE, ZnO, LiF, PFN-Br, BCP, and C. 60 The second modification layer is prepared from materials such as SnO2, Ca, or Mg; the second modification layer is prepared from materials such as PEDOT:PSS, MoO3, NPB, PVK, or NiO; the second transparent conductive electrode is the anode, and its preparation material is Ag, Al, or Au.

4. The three narrow-wavelength organic photodetector as described in claim 1, characterized in that, The filter layer is a mixed membrane layer of F8T2 donor and ITIC-Th acceptor with a thickness of 200nm-500nm and a donor to acceptor mass ratio of (4-7):

10.

5. A method for fabricating a three-narrow-wavelength organic photodetector as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1. Clean the transparent substrate, dry it, and then perform ultraviolet ozone cleaning; Step 2. A first transparent conductive electrode is fabricated on the front side of the cleaned transparent substrate using a deposition method; Step 3. A first modification layer is prepared on the surface of the first transparent conductive electrode by spin coating, and then thermally annealed in an air atmosphere after spin coating; Step 4. Preparation of photosensitive layer solution: The first donor material and the first acceptor material are placed in the first organic solvent, and then the solution is stirred and mixed at a certain temperature. After stirring, the photosensitive layer solution is obtained. Step 5. In a nitrogen atmosphere, a photosensitive layer solution is spin-coated onto the surface of the first transparent conductive electrode using a spin-coating process. After spin-coating, a thermal annealing treatment is performed to obtain the photosensitive layer. Step 6. Prepare a second modification layer on the surface of the photosensitive layer using a vacuum evaporation method; Step 7. Prepare a second transparent conductive electrode on the surface of the second modified layer by vapor deposition; Step 8. Preparation of filter layer solution: Place the second donor material and the second acceptor material into the second organic solvent, and then stir and mix the solution at a certain temperature. After stirring, the filter layer solution can be obtained. Step 9. In a nitrogen atmosphere, a filter layer is prepared on the back side of a transparent substrate using spin coating. After completion, the desired three-narrow-wavelength organic photodetector can be obtained.

6. The preparation method according to claim 5, characterized in that, The absorption end wavelength of the second receptor absorption spectrum is shorter than the end wavelength of the response band of the photosensitive layer.

7. The preparation method according to claim 5, characterized in that, In addition to spin coating, the preparation methods of the filter layer, the first cathode modification layer, the second cathode modification layer and the photosensitive layer can also be spin coating, blade coating, drop coating or spray coating; if the filter layer is prepared by spin coating, the spin coating speed is 300-700 rpm, and the corresponding film thickness is 230nm-460nm.

8. The preparation method according to claim 5, characterized in that, The filter layer material of the three narrow-wavelength photodetector is a hybrid film of F8T2 and ITIC-Th. The process of the device with optimal performance is as follows: the concentration of the filter layer solution is 34 mg / ml, the donor-acceptor ratio is 5:10, and the spin coating speed is 700 rpm.

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