Three-narrow-band organic photoelectric detector based on back filtering structure and preparation method of three-narrow-band organic photoelectric detector

Abstract

The invention provides a three-narrow-band organic photoelectric detector based on a back filtering structure and a preparation method, and belongs to the technical field of organic photoelectric detectors. According to the organic photoelectric detector, the organic filter layer is prepared on the outer side of the incident substrate, and the three-narrow-band detection of the specific wave band can be realized by selecting the filter layer material matched with the response wave band of the photosensitive layer and adjusting the components, the ratio and the film thickness of the filter layer. The three-narrow-band organic photoelectric detector designed by the invention simultaneously has selective response at three wave bands of 340nm ultraviolet light, 540nm green light and 760nm red light, the EQE corresponding to each wave band can respectively reach 5%, 20% and 15%, the FWHM is respectively about 60nm, 40nm and 40nm, the three-narrow-band organic photoelectric detector can be applied to the fields of encrypted optical communication, feature target identification and the like according to verification, and the three-narrow-band organic photoelectric detector disclosed by the invention is simple in structure and low in cost. The preparation process is simple.

Description

Technical Field

[0001] The invention belongs to the technical field of organic photoelectric detectors, and in particular relates to a triple narrow-wavelength organic photoelectric detector based on a back-side light filtering structure and a preparation method thereof. Background Art

[0002] Narrow-band photodetectors refer to photodetectors that have selective response characteristics to specific narrow bands, that is, bands with a response peak half-width (FWHM) less than 100nm. Compared with traditional wide-band photodetectors, this type of detector has fine spectral recognition capabilities and has a wide range of applications in defense and military industry, encrypted optical communications, specific gas detection, biological monitoring of specific bands, and other fields. With the development of the information age, special applications such as multi-spectral detection and multi-band feature target recognition are constantly developing. Due to its rich feature information capture capabilities, multi-narrow-wavelength optical detection has shown more significant advantages in target recognition under complex backgrounds, complex encrypted optical communications, and other fields. Therefore, industrial transformation and upgrading and information development have put forward requirements for the research of multi-narrow-wavelength photodetectors.

[0003] The traditional implementation of multi-narrow-band photodetectors often relies on adding optical elements (such as gratings, beam splitters, filters or micro-surface structures, etc.) to wide-band inorganic photodetectors. These methods undoubtedly limit the miniaturization, lightness and integration of the detection system. In terms of organic photodetectors, schemes such as charge collection narrowing (Nat. Commun., 2015, 6, 6343.), charge injection narrowing (Adv. Opt. Mater., 2018, 6, 1800249.) and self-filtering narrowing (ACS Appl. Mater. Interfac es, 2020, 12, 13061–13067.) have been used to realize single narrow-band organic photodetectors, but multi-narrow-band photodetectors either rely on the array structure design of external microcavities with complex structure, difficult preparation, and complex subsequent readout circuits and algorithms (Adv. Mater., 2017, 29, 1702184.), or rely on the design of organic materials with multi-band absorption characteristics that are scarce and difficult to design.

[0004] Therefore, it is of great significance to design a simple structural unit detection device to achieve multi-narrow wave photoelectric detection performance. Summary of the invention

[0005] In view of the problems existing in the background technology, the purpose of the present invention is to provide a three-narrow-wave organic photodetector based on a back-side filter structure and a preparation method. The organic photodetector prepares an organic filter layer on the outside of the incident substrate, selects a filter layer material that matches the response band of the photosensitive layer, and adjusts the composition, ratio and film thickness of the filter layer, thereby realizing three narrow-wave detection of a specific band. The device structure of the present invention is simple and the preparation process is simple.

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

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

[0008] Wherein, the photosensitive layer is a bulk heterojunction with a wide-band response;

[0009] The absorption starting wavelength of the absorption spectrum of the filter layer material should be greater than the starting value of the response band of the photosensitive layer material to achieve a narrow-band response at the start of the response; the absorption ending wavelength of the absorption spectrum of the filter layer material should be less than the ending value of the response band of the photosensitive layer material to achieve a narrow-band response at the end band of the photosensitive layer response; and the absorption valley in the absorption spectrum of the filter layer material needs to correspond to the middle band of the three response bands of the three narrow-wave 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 middle response band of the triple narrow-wave organic photodetector narrower, preferably below 100 nm; 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 band of the bulk heterojunction is in the range of 300nm-800nm.

[0012] Furthermore, the three-narrow-wavelength organic photodetector is an inversion device structure, the first transparent conductive electrode is a cathode, and its preparation material is preferably ITO, PEDOT:PSS, graphene or silver nanowires; the first modification layer is preferably prepared by PEIE, ZnO, LiF, PFN-Br, BCP, C 60 , SnO2, Ca or Mg; the material for preparing the second modification layer is preferably 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 film layer obtained by F8T2 donor and ITIC-Th acceptor, the film thickness is 200nm-500nm, and the mass ratio of donor to acceptor is (4-7):10.

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

[0015] F8T2 has a weak absorption at 340nm, the absorption tail of ITIC-Th is slightly blue-shifted relative to the tail of the response band of the photosensitive layer, and the mixed film of F8T2 and ITIC-Th has an absorption valley near 540nm. Based on the above characteristics, three narrow wave responses near 340nm, 540nm and 760nm can be achieved.

[0016] A method for preparing a triple narrow-wavelength organic photodetector based on a back-side filter structure comprises the following steps:

[0017] Step 1. Clean the transparent substrate, blow dry it and then clean it with UV ozone;

[0018] Step 2. preparing a first transparent conductive electrode on the front side of the cleaned transparent substrate by a deposition method;

[0019] Step 3. Prepare a first modified layer on the surface of the first transparent conductive electrode by spin coating, and perform thermal annealing in air atmosphere after spin coating;

[0020] Step 4. preparing a photosensitive layer solution: placing the first donor material and the first acceptor material into a first organic solvent, and then stirring and mixing the solution at a certain temperature, and obtaining a photosensitive layer solution after the stirring is completed;

[0021] Step 5. In a nitrogen atmosphere, a photosensitive layer solution is spin-coated on the surface of the first transparent conductive electrode by a spin coating process, and a thermal annealing treatment is performed after the spin coating is completed to obtain a photosensitive layer;

[0022] Step 6. preparing a second modification layer on the surface of the photosensitive layer by vacuum evaporation;

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

[0024] Step 8. Prepare a filter layer solution: put the second donor material and the second acceptor material into a second organic solvent, and then stir and mix the solution at a certain temperature, and after the stirring is completed, a filter layer solution can be obtained;

[0025] Step 9. In a nitrogen atmosphere, a filter layer is prepared on the back of the transparent substrate by spin coating. After completion, the desired triple narrow-band 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, the preparation methods of the filter layer, the first cathode modification layer, the second cathode modification layer and the photosensitive layer may be substituted by spin coating, scraping, dripping or spraying in addition to spin coating.

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

[0029] Furthermore, the filter layer material of the triple narrow-wavelength photodetector is a mixed film of F8T2 and ITIC-Th, and the process of the device with the best 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 (corresponding to a film thickness of about 230 nm).

[0030] The mechanism of the present invention is: a filter layer having a specific matching characteristic between the absorption spectrum and the response band of the photosensitive layer is prepared on the back of the incident substrate of the organic photodetector to realize three narrow-wave organic photoelectric detection. Specifically, the weak absorption band of the filter layer should correspond to the three narrow-wave bands to be realized and cover the response range of the photosensitive layer; more specifically, the absorption starting wavelength of the filter layer is slightly larger than the response starting wavelength of the photosensitive layer, the absorption ending wavelength is slightly smaller than the response ending wavelength of the photosensitive layer, the wavelength at the absorption valley corresponds to the third narrow band, and the absorption coefficient at the absorption valley is sufficiently low and the absorption valley is sufficiently narrow. By selecting suitable filter layer materials and adjusting the film thickness of the filter layer, flexible adjustment of the narrow band of device response 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) The present invention innovatively proposes to adjust the response band of the device by adjusting the weak absorption band of the filter layer, that is, regulating the absorption starting wavelength, absorption ending wavelength and absorption valley of the filter layer. The three-narrow-wave organic photodetector designed by the present invention has selective response at the three bands of ultraviolet 340nm, green light 540nm and red light 760nm at the same time. The EQE corresponding to each band can reach 5%, 20% and 15% respectively, and the FWHM is approximately 60nm, 40nm and 40nm respectively. The three-narrow-wave photodetector has been verified to be applicable to encrypted optical communication, feature target recognition and other fields.

[0033] (2) The preparation process of the present invention is simple and has good compatibility, and can be widely used in the field of organic narrow-wavelength photodetectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1It is a schematic structural diagram of an organic photodetector based on a back-side filtering structure in the present invention.

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

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

[0037] Figure 3 This is the EQE response spectrum of the triple narrow-wavelength organic photodetector prepared in Example 1.

[0038] Figure 4 This is a JV curve diagram of the triple narrow-wavelength organic photodetector prepared in Example 1.

[0039] Figure 5 EQE response spectra of the three narrow-wavelength organic photodetectors prepared in Example 1 and Example 2;

[0040] Among them, 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 spin coating speeds with the same ratio.

[0041] Figure 6 This is the EQE response spectrum of the regulation process of the three-narrow-wavelength organic photodetector prepared in Comparative Example 1. DETAILED DESCRIPTION

[0042] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the implementation modes and the accompanying drawings.

[0043] A triple narrow-wavelength organic photodetector based on a back-side filtering structure, the structural schematic diagram of which is shown in FIG. Figure 1 As shown, from bottom to top are an organic filter layer (Filter), a transparent substrate (Glass), a first transparent conductive electrode (ITO), a first modified layer (ZnO), a photosensitive layer (PBDB-T:ITIC-Th), a second modified layer (MoO3) and a second transparent conductive electrode (Ag);

[0044] Wherein, the photosensitive layer is a bulk heterojunction layer with wide-band response prepared by an organic donor and an organic acceptor;

[0045] The starting value of the absorption peak of the filter layer material should be smaller than the starting value of the response of the photosensitive layer material, so as 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 starting band of the photosensitive layer material); the ending value of the absorption peak of the filter layer material should be larger than the starting value of the response of the photosensitive layer material, so as to achieve a narrow-band response at the end of the absorption peak; and the absorption valley of the filter layer material needs to correspond to the middle band of the three narrow bands.

[0046] Example 1

[0047] A method for preparing a triple narrow-wavelength organic photodetector based on a back-side filter structure comprises the following steps:

[0048] Step 1. The transparent substrate with ITO deposited on one side is ultrasonically cleaned with detergent, deionized water, acetone and isopropanol in sequence, dried with nitrogen, and then cleaned with ultraviolet ozone for 20 minutes to obtain a transparent substrate with the first transparent conductive electrode ITO deposited thereon;

[0049] Step 2. Prepare the first modified layer ZnO on the surface of the first transparent conductive electrode ITO by spin coating, prepare the ZnO precursor solution on the ITO cathode by spin coating, the spin coating speed and time are 4000 rpm and 40 s respectively, and perform thermal annealing in air atmosphere, the temperature and time of thermal annealing are 200° C. and 30 min respectively;

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

[0051] Step 4. In a nitrogen atmosphere, a photosensitive layer solution is spin-coated on the surface of the ZnO electrode by a spin coating process. The spin coating speed and time are 2000 rpm and 40 s respectively. After the spin coating is completed, a thermal annealing treatment is performed at 110° C. for 10 min to obtain a photosensitive layer PBDB-T:ITIC-Th.

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

[0053] Step 6. Prepare the second transparent conductive electrode Ag on the surface of the second modified layer MoO3 by evaporation method, and the evaporation pressure is 10 -4 Pa, thickness is 100nm;

[0054] Step 7. Prepare the filter layer solution: use F8T2 as the donor material and ITIC-Th as the acceptor material in a mass ratio of 5:10, use chlorobenzene as the organic solvent, prepare the filter layer solution, and the total concentration of the solution is 34 mg / ml; then place the solution on a heated stirring table at 55°C and stir for more than 12 hours, and the filter layer solution can be obtained after the stirring is completed;

[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 the spin coating, the desired triple narrow-wavelength organic photodetector can be obtained.

[0056] Figure 2 The normalized absorption spectra of the photosensitive layer and filter layer material films used in Example 1 of the present invention are shown in Figure (a). Specifically, they include: Figure (a) the absorption spectra of the three organic materials used in the device, and Figure (b) the absorption spectrum of the filter layer F8T2:ITIC-Th. PBDB-T:ITIC-Th is used as the photosensitive layer material, and its absorption spectrum ranges from 300nm to 800nm. F8T2 and ITIC-Th are used as the filter layer materials, and the absorption spectrum range of F8T2 is from 300nm to 520nm, and the absorption spectrum range of ITIC-Th is from 540nm to 800nm. The mixed filter film F8T2:ITIC-Th shows the weakest absorption before 340nm, near 540nm, and after 760nm.

[0057] Figure 3 This is the EQE response spectrum of the three-narrow-wavelength organic photodetector prepared in Example 1. Its response spectrum has narrow-wavelength responses in the three bands of 340nm, 540nm and 760nm, and the FWHM are 60nm, 40nm and 40nm respectively.

[0058] Figure 4 The JV curve of the three narrow-wavelength organic photodetector prepared in Example 1 includes the dark current density of the device, the photocurrent density at 340nm, the photocurrent density at 540nm, and the photocurrent density at 760nm. The performance characterization results are as follows: Under standard test conditions, when the device is biased at -0.5V, the dark current density of the device is measured to be 1.36×10 - 8 A / cm 2 , at UV 340nm (0.145mW / cm 2 )、Green light 540nm (0.574mW / cm 2 ), red light 760nm (0.417mW / cm 2 ) The photocurrent density of the three bands is 3.44×10 -5 A / cm 2 , 5.02×10-5 cm 2 , 3.34×10 -6 / cm 2 , EQE are 5%, 20%, and 15% respectively, and FWHM are 60nm, 40nm, and 40nm respectively.

[0059] Example 2

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

[0061] Comparative Example 1

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

[0063] The EQE response spectra of the control process of the three narrow-wavelength organic photodetectors prepared in Example 1, Example 2 and Comparative Example 1 are shown in FIG. 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 to adjust the response band of the device.

[0064] Adjusting the thickness of the filter layer not only affects the EQE peak size of the organic photodetector, but also affects the half-width of the device response peak. Specifically, under the same ratio, as the thickness of the filter layer increases, the EQE in the 340nm band gradually decreases to close to 0 and the half-width becomes smaller, and the response at 540nm and 760nm also gradually decreases. The mass ratio of different donors mainly affects the peak half-width of the device. As the proportion of F8T2 increases, the peak half-width of the device at 340nm and 540nm will decrease. That is, the regulation of the ratio mainly affects the EQE ratio and the peak half-width of the device at different peaks. At the same concentration and the same spin coating speed, as the proportion of F8T2 donors increases, the thickness of the filter layer will increase, so the overall EQE of the device will decrease. At the same time, due to the increase in the proportion of donors, the ratio of the transmittance of the filter layer before 540nm to the transmittance after 540nm will decrease. This is reflected in the EQE spectrum of the three narrow-wavelength photodetectors, namely: overall, the responses at each peak are reduced, and the ratio of the peak EQE at 340nm and 540nm to the peak EQE at 760nm decreases. At the same time, the FWHM before 540nm becomes narrower and the FWHM after 540nm becomes wider.

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

[0066] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A triple narrow-band organic photodetector based on a back-side filter structure, characterized in that: From bottom to top, there are an organic filter layer, a transparent substrate, a first transparent conductive electrode, a first modified layer, a photosensitive layer, a second modified layer, and a second transparent conductive electrode; Wherein, the photosensitive layer is a bulk heterojunction with a wide-band response; The absorption starting wavelength of the absorption spectrum of the filter layer material should be greater than the starting value of the response band of the photosensitive layer material to achieve a narrow-band response at the start of the response; the absorption ending wavelength of the absorption spectrum of the filter layer material should be less than the ending value of the response band of the photosensitive layer material to achieve a narrow-band response at the end band of the photosensitive layer response; and the absorption valley in the absorption spectrum of the filter layer material needs to correspond to the middle band of the three response bands of the three narrow-wave organic photodetector.

2. The triple narrow-wavelength organic photodetector according to claim 1, characterized in that: 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 middle response band of the three narrow-wave organic photodetector below 100nm; the lower the absorption coefficient of the absorption valley, the better.

3. The triple narrow-wavelength organic photodetector according to claim 1, characterized in that: The organic donor of the photosensitive layer is PBDB-T, the organic acceptor is ITIC-Th, and the response band of the bulk heterojunction is 300nm-800nm.

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

5. The triple narrow-wavelength organic photodetector according to claim 1, characterized in that: The filter layer is a mixed film layer obtained by F8T2 donor and ITIC-Th acceptor, the film thickness is 200nm-500nm, and the mass ratio of the donor and the acceptor is (4-7):

10.

6. The triple narrow-band organic photodetector according to any one of claims 1 to 5, characterized in that: The central wavelengths of the response bands of the three narrow-wavelength organic photodetectors are 340 nm, 540 nm and 760 nm.

7. A method for preparing a triple narrow-band organic photodetector based on a back-side filter structure, characterized in that: The following steps are involved: Step 1. Clean the transparent substrate, blow dry it and then clean it with UV ozone; Step 2. preparing a first transparent conductive electrode on the front side of the cleaned transparent substrate by a deposition method; Step 3. Prepare a first modified layer on the surface of the first transparent conductive electrode by spin coating, and perform thermal annealing in air atmosphere after spin coating; Step 4. preparing a photosensitive layer solution: placing the first donor material and the first acceptor material into a first organic solvent, and then stirring and mixing the solution at a certain temperature, and obtaining a photosensitive layer solution after the stirring is completed; Step 5. In a nitrogen atmosphere, a photosensitive layer solution is spin-coated on the surface of the first transparent conductive electrode by a spin coating process, and a thermal annealing treatment is performed after the spin coating is completed to obtain a photosensitive layer; Step 6. preparing a second modification layer on the surface of the photosensitive layer by vacuum evaporation; Step 7. Prepare a second transparent conductive electrode on the surface of the second modified layer by evaporation; Step 8. Prepare a filter layer solution: put the second donor material and the second acceptor material into a second organic solvent, and then stir and mix the solution at a certain temperature, and after the stirring is completed, a filter layer solution can be obtained; Step 9. In a nitrogen atmosphere, a filter layer is prepared on the back of the transparent substrate by spin coating. After completion, the desired triple narrow-band organic photodetector can be obtained.

8. The preparation method according to claim 7, characterized in that: The absorption end wavelength of the second receptor absorption spectrum is smaller than the end wavelength of the response band of the photosensitive layer.

9. The preparation method according to claim 7, 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 replaced by spin coating, scraping, drip coating or spraying; if the filter layer is prepared by spin coating, the spin coating speed is 300-700rpm, and the corresponding film thickness is about 230nm-460nm.

10. The preparation method according to claim 7, characterized in that: The filter layer material of the triple narrow-wavelength photodetector is a mixed film of F8T2 and ITIC-Th. The process of the device with the best 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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