A quantum dot photodetection device, array and method of fabrication thereof

Abstract

The application discloses a quantum dot light detection device, which comprises a functional layer, wherein the functional layer is a multilayer structure, and at least a P-type semiconductor layer, a colloidal quantum dot layer and an N-type semiconductor layer are arranged in sequence in the multilayer structure; the P-type semiconductor layer is selected from one of inorganic semiconductor materials and metal complexes of a large conjugate system; at least one of the P-type semiconductor layer and the N-type semiconductor layer is an organic semiconductor material; and the metal complexes of the large conjugate system are selected from one or more of phthalocyanine lead and derivatives thereof. In the technical scheme, the organic semiconductor can make up for the absorption and response of a pure inorganic quantum dot light detection device in a specific wave band. The organic semiconductor in the application can passivate surface defects of inorganic quantum dots, so that the light response is further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optoelectronic technology, in particular to a quantum dot light detection device, array and preparation method thereof. BACKGROUND

[0002] Colloidal quantum dot light detector is one of the important branches of photodetector, due to its low cost, potential advantages in preparation of large area and flexible optoelectronic devices, and excellent photoelectric efficiency, it has been widely concerned in the fields of solar cells, light emitting diodes, lasers, detectors and displays, especially, it has great application potential in spectral detection and imaging field.

[0003] Generally, quantum dot material will appear a quantum size related absorption peak at the long wavelength absorption edge due to quantum confinement effect, and there is an absorption trough between the absorption peak and bulk absorption wavelength, which is not conducive to the application of wide wavelength.

[0004] And with the red shift of wavelength, the corresponding quantum dot nanocrystal size increases, because the minimum surface energy needs to be maintained, large size quantum dots will expose different crystal faces, and it is difficult to passivate.

[0005] Therefore, it is urgent to find a technical solution to solve the defects existing in the prior art. SUMMARY

[0006] The present application discloses a kind of multilayer heterojunction of organic semiconductor-inorganic quantum dot, by introducing organic semiconductor material to make up the weak absorption band of quantum dot material.Simultaneously, by the heteroatom and π electron cloud contained in organic semiconductor material, the passivation effect on quantum dot surface is enhanced.

[0007] In addition, the array of organic-inorganic quantum dot heterojunction light detector prepared based on the technical scheme of the present application has ideal external quantum efficiency.

[0008] One object of the present application is to provide a quantum dot light detection device, which comprises a functional layer,

[0009] wherein,

[0010] the functional layer is a multilayer structure,

[0011] in the multilayer structure, at least a P-type semiconductor layer, a colloidal quantum dot layer and an N-type semiconductor layer are sequentially arranged;

[0012] the P-type semiconductor layer is selected from one of inorganic semiconductor material or metal complex of large conjugated system;

[0013] The P-type semiconductor layer and the N-type semiconductor layer are at least one layer of organic compound material.

[0014] Further, the metal complex of the large conjugated system is selected from one or more of lead phthalocyanine and its derivatives.

[0015] We found that for the (111) crystal surface of PbS colloidal quantum dots, it is mainly composed of semi-coordinated Pb atoms, has a high affinity, and is easy to combine with electron-donating X-type ligands, thereby achieving surface passivation; and its (100) crystal surface is a non-polar surface, which is composed of metal atoms, heavy metal atoms, and / or S atoms, and it is difficult to passivate the above atoms, so it needs to be combined with neutral L-type ligands to reduce the surface energy. With the increase of the size of the quantum dots, the (100) crystal surface of the colloidal quantum dots is gradually increased, and the passivation difficulty is gradually increased.

[0016] We unexpectedly found that using lead phthalocyanine and its derivatives as the P-type semiconductor layer can effectively passivate the (100) crystal surface of the larger colloidal quantum dots with a wavelength greater than 900 nm.

[0017] Further, the colloidal quantum dot layer is selected from one or more of GaP, ZnSe, ZnS, CuO, CuO2, CuS, CuSe, CuInS2, CuInSe2, CuInGaSe, CuInGaS, Ge, PbS, PbSe, HgTe or AgBiS2.

[0018] Further, the thickness of the colloidal quantum dot layer is 10-1000 nm.

[0019] Further, the thickness of the P-type semiconductor layer is 1-300 nm.

[0020] Further, the material of the N-type semiconductor layer is selected from one or more of the following structures:

[0021]

[0022]

[0023] Wherein, the M is selected from the main group elements of I, II, III, IV, or transition elements and their compounds.

[0024] Further, the thickness of the N-type semiconductor layer is 1-300 nm.

[0025] Further, the quantum dot light detection device is selected from a forward structure or a flip-chip structure.

[0026] Further, the quantum dot photodetector device comprises, in sequence, a bottom electrode, a bottom electrode interface layer, a functional layer, a top electrode interface layer, a top electrode and a packaging layer.

[0027] Further, the functional layer comprises P-type semiconductor layers, colloidal quantum dot layers and N-type semiconductor layers which are alternately stacked in any order.

[0028] Further, the materials of the bottom electrode interface layer and the top electrode interface layer are selected from one or more of metal oxides, metal nitrides, metal sulfides or metal halides.

[0029] Further, the thickness of the bottom electrode interface layer and the top electrode interface layer is 1-300 nm.

[0030] Another object of the present application is to provide a preparation method of the quantum dot photodetector device as described above, comprising the following steps:

[0031] (1) substrate cleaning;

[0032] (2) bottom electrode film formation and ultraviolet irradiation or oxygen plasma cleaning;

[0033] (3) bottom electrode interface layer film formation;

[0034] (4) P-type semiconductor layer preparation;

[0035] (5) colloidal quantum dot layer preparation;

[0036] (6) N-type semiconductor layer preparation;

[0037] (7) top electrode interface layer film formation;

[0038] (8) top electrode preparation;

[0039] (9) packaging layer preparation.

[0040] Further, the colloidal quantum dot film preparation comprises the following steps:

[0041] The colloidal quantum dot layer preparation adopts a one-step film formation method after solution phase ligand exchange or a step-by-step film formation method after solid state ligand exchange.

[0042] Further, the P-type semiconductor layer preparation and the N-type semiconductor layer preparation comprise the following steps:

[0043] The P-type semiconductor layer preparation and the N-type semiconductor layer preparation, and the functional layer film preparation adopt one or more of solution film formation, vacuum thermal evaporation deposition, magnetron sputtering, atomic layer deposition and chemical vapor deposition.

[0044] Further, the preparation of the bottom electrode interface layer, top electrode interface layer, bottom electrode, top electrode is independently selected from one or more of solution film forming, sol-gel film forming, vacuum thermal evaporation, atomic layer deposition, chemical vapor deposition, electrodeposition, anodic oxidation method.

[0045] Further, the preparation of the encapsulation layer is selected from one of vacuum thermal evaporation, chemical vapor deposition, atomic layer deposition, plasma sputtering, liquid film forming method.

[0046] Another object of the present application is to provide a colloidal quantum dot photodetector array formed by arranging the above quantum dot photodetector device, which sequentially comprises a substrate, a periodically arranged lower electrode array, a lower electrode interface layer, a photosensitive layer, an upper electrode interface layer and a common electrode layer.

[0047] Further, the lower electrode interface layer, photosensitive layer, upper electrode interface layer and common electrode layer are all continuous structures in the colloidal quantum dot photodetector region.

[0048] Further, the lower electrode interface layer, photosensitive layer, upper electrode interface layer and common electrode layer are all not subjected to inter-pixel patterning treatment.

[0049] Further, the lower electrode interface layer completely covers the lower electrode array.

[0050] Further, the substrate comprises a pixel readout circuit composed of a silicon-based complementary metal oxide semiconductor transistor or a thin film transistor.

[0051] Compared with the prior art, the present application has the following beneficial effects:

[0052] 1. In the technical scheme of the present application, the organic semiconductor can make up for the absorption and response of pure inorganic quantum dot photodetector devices in a specific waveband.

[0053] 2. In the present application, the surface defects of inorganic quantum dots are passivated by using organic semiconductors, thereby further improving the light response. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 The device structure of the colloidal quantum dot photodetector of Examples 1-2 and the comparative example is shown.

[0055] Figure 2 The top view structure of the substrate of the colloidal quantum dot photodetector array based on Examples 1-2 and the comparative example is shown,

[0056] wherein,

[0057] Figure 2 a pixel definition layer is covered, and the encapsulation layer is omitted; Figure 2b omit the encapsulation layer and the pixel definition layer.

[0058] Figure 3 A comparison chart of external quantum efficiency of the colloidal quantum dot photodetector array of Example 1-2 and the comparative example is shown.

[0059] Figure 4 Another technical solution of the present application is shown, i.e. the array structure in the case of high-density pixels.

[0060] Reference signs:

[0061] Glass substrate - 200, metal pin - 201, lower electrode array - 202, bottom electrode interface layer - 203, P-type semiconductor layer - 204, colloidal quantum dot layer - 205, N-type semiconductor layer - 206, top electrode modification layer - 207, top electrode - 208, encapsulation layer - 209, pixel definition layer - 210;

[0062] Pixel readout circuit - 301, bottom electrode array - 302, bottom electrode interface layer - 303, heterojunction layer (P-type semiconductor layer + quantum dot layer + N-type semiconductor layer) - 304, top electrode interface layer - 305, common electrode layer - 306, encapsulation layer - 307. DETAILED DESCRIPTION

[0063] In order to more clearly illustrate the technical solutions of the present application, the following examples are listed, but the present application is not limited thereto.

[0064] The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0065] Figure 1 The device structure of the quantum dot photodetector of the present application is shown.

[0066] Figure 2 The top view structure of the substrate of the colloidal quantum dot photodetector array of the present application is shown, wherein, Figure 2 a covered with a pixel definition layer, omitting the encapsulation layer; Figure 2 b omit the encapsulation layer and the pixel definition layer. The cross-sectional view cut along the dotted line corresponds Figure 1 .

[0067] Figure 2 a The top view structure of the substrate of the colloidal quantum dot photodetector array is shown, which is covered with a pixel definition layer, and the working area of the pixel is defined by the patterned bottom electrode, wherein there is a metal lead between the electrode 202 and the pin, which is covered by the insulated pixel definition layer; Figure 2b shows the top view structure of the substrate of the colloidal quantum dot photodetector array, which removes the pixel definition layer, clearly showing the electrode pins of the pixel array substrate connected with the bottom electrode.

[0068] The preparation method of the colloidal quantum dot material in the embodiment and the comparative example is as follows: the lead sulfide colloidal quantum dots prepared by the laboratory of the present application by using conventional means are prepared into the colloidal quantum dot material through sequential spin coating and ligand exchange.

[0069] The N-type organic molecule D2 in the embodiment has the following molecular structure formula, which is prepared by the present application.

[0070]

[0071] Embodiment 1

[0072] A quantum dot photodetector device, the structure of which is as follows from bottom to top: glass substrate 200 (0.7 mm) / lower electrode array 202 (silver, 100 nm) / bottom electrode interface layer 203 (molybdenum oxide, 4 nm) / P-type semiconductor layer 204 (EDT ligand exchanged PbS quantum dots, 30 nm) / colloidal quantum dot layer 205 (200 nm) / N-type semiconductor layer 206 (D2, 30 nm) / top electrode interface layer 207 (zinc oxide, 30 nm) / top electrode ITO 208 (100 nm) / encapsulation layer 209 (epoxy resin); wherein the exposed area of the lower electrode array 202 is limited by the pixel definition layer 210 (photoresist SU8) and is led out to the outer surface of 209; the top electrode 208 is led out to the outer surface of 209 through the pre-embedded contact 201.

[0073] A colloidal quantum dot photodetector array is prepared based on the quantum dot photodetector. The pixel size of the colloidal quantum dot photodetector array is limited to 1.6*1.6 mm by the insulating pixel definition layer 2 , the pixel pitch is 2.4 mm, and the number of pixels is 4*8.

[0074] The preparation method of the colloidal quantum dot photodetector array comprises the following steps:

[0075] S1. Place the substrate on a film washing rack and use an ultrasonic cleaner to ultrasonically clean for 1 min, and the detergent is isopropyl alcohol;

[0076] S2. A layer of 4 nm molybdenum oxide is evaporated on the cleaned lower electrode array through a mask plate;

[0077] S3. A layer of lead sulfide quantum dot material is spin-coated, and EDT methanol solution is used for ligand exchange;

[0078] S4. Continue spin-coating the lead sulfide quantum dot material, and use TBAI methanol solution to perform ligand exchange, repeat the two-step operation until a colloidal quantum dot film of a specified thickness (200 nm) is formed;

[0079] S5. Dissolve D2 in chloroform solution, spin-coat into a 30 nm thin film;

[0080] S6. Use laser to remove the residual film above the pin, expose the metal pin and top electrode contact;

[0081] S7. Sputter a specified thickness of ITO top electrode through another patterned mask plate;

[0082] S8. After device preparation, cure and package with epoxy resin under ultraviolet light.

[0083] Example 2

[0084] A quantum dot light detection device, the structure of which is as follows from bottom to top: glass substrate 200 (0.7 mm) / lower electrode array 202 (silver, 100 nm) / bottom electrode interface layer 203 (molybdenum oxide, 4 nm) / P-type semiconductor layer 204 (lead phthalocyanine, 30 nm) / colloidal quantum dot layer 205 (200 nm) / N-type semiconductor layer 206 (D2, 30 nm) / top electrode interface layer 207 (zinc oxide, 30 nm) / top electrode ITO 208 (100 nm) / packaging layer 209 (epoxy resin); wherein the exposed area of the lower electrode array 202 is limited by the pixel definition layer 210 (photoresist SU8) and is led out to the outer surface of 209; the top electrode 208 is led out to the outer surface of 209 through the pre-embedded contact 201.

[0085] A colloidal quantum dot light detector array is prepared based on the quantum dot light detector. The pixel size of the colloidal quantum dot light detector array is limited to 1.6 x 1.6 mm by the insulating pixel definition layer 2 , the pixel pitch is 2.4 mm, and the number of pixels is 4 x 8.

[0086] The preparation method of the colloidal quantum dot light detector array comprises the following steps:

[0087] S1. Place the substrate on a film washing rack and use an ultrasonic cleaner to ultrasonically clean for 1 min, with isopropyl alcohol as the detergent;

[0088] S2. Evaporate a layer of 4 nm molybdenum oxide on the cleaned lower electrode array through a mask plate;

[0089] S3. Continue to evaporate a layer of 30 nm lead phthalocyanine;

[0090] S4. Spin-coating PbS quantum dot material, ligand exchange using TBAI in methanol solution, repeat two-step operation until a PbS quantum dot film of specified thickness (200 nm) is formed;

[0091] S5. Dissolve D2 in chloroform solution, spin-coat into a 30 nm thin film;

[0092] S6. Use laser to remove residual film above the pin, expose the metal pin and top electrode contact;

[0093] S7. Sputter a specified thickness of ITO top electrode through another patterned mask plate;

[0094] S8. After device preparation, cure and package with epoxy resin under UV light.

[0095] Example 3

[0096] A quantum dot photodetector device, the structure of which is as follows from bottom to top: glass substrate 200 (0.7 mm) / lower electrode array 202 (silver, 100 nm) / bottom electrode interface layer 203 (molybdenum oxide, 4 nm) / P-type semiconductor layer 204 (lead phthalocyanine, 30 nm) / colloidal quantum dot layer 205 (200 nm) / N-type semiconductor layer 206 (fullerene C60, 30 nm) / top electrode interface layer 207 (zinc oxide, 30 nm) / top electrode ITO 208 (100 nm) / packaging layer 209 (epoxy resin); wherein the exposed area of the lower electrode array 202 is limited by the pixel definition layer 210 (photoresist SU8) and is led out to the outer surface of 209; the top electrode 208 is led out to the outer surface of 209 through the pre-embedded contact 201.

[0097] A colloidal quantum dot photodetector array is prepared based on the quantum dot photodetector. The pixel size of the colloidal quantum dot photodetector array is limited to 1.6 x 1.6 mm by the insulating pixel definition layer 2 , the pixel pitch is 2.4 mm, and the number of pixels is 4 x 8.

[0098] The preparation method of the colloidal quantum dot photodetector array comprises the following steps:

[0099] S1. Place the substrate on a film washing rack and clean it using an ultrasonic cleaner for 1 min with isopropyl alcohol as the detergent;

[0100] S2. Evaporate a layer of 4 nm molybdenum oxide on the cleaned lower electrode array through a mask plate;

[0101] S3. Continue to evaporate a layer of 30 nm lead phthalocyanine;

[0102] S4. Spin-coating PbS quantum dot material, ligand exchange using TBAI in methanol solution, repeating two-step operation until forming PbS quantum dot film with specified thickness (200 nm);

[0103] S5. Evaporating a 30 nm film of fullerene C60;

[0104] S6. Using laser to remove residual film above the pin, exposing the metal pin and top electrode contact;

[0105] S7. Sputtering ITO top electrode with specified thickness through another patterned mask plate;

[0106] S8. After device preparation, curing and packaging with epoxy resin under UV light.

[0107] Comparative Example

[0108] A quantum dot light detection device, the difference between the comparative example and Example 1 is that nickel oxide is used as the P-type semiconductor layer, and fullerene C60 is used as the N-type semiconductor layer, and other structures and preparation methods are the same as Example 1.

[0109] Test Example

[0110] The photoelectric performance of the colloidal quantum dot light detection device array prepared in Examples 1-2 and the comparative example is tested. The test method used for each index is a conventional means familiar to those skilled in the art.

[0111] The test result image is shown in Figure 3 , and the related EQE data is shown in Table 1.

[0112] Table 1 EQE values of colloidal quantum dot light detection device arrays based on Examples 1-2 and the comparative example

[0113] Sample EQE @ 840 nm EQE @ 940 nm EQE @ 1140 nm EQE @ 1540 nm Example 1 28％ 24.4％ 10.8％ 30.7％ Example 2 27.5％ 22.4％ 16.3％ 33.8％ Comparative Example 13.5％ 9.28％ 6.21％ 21.6％

[0114] Figure 3 A comparison diagram of the external quantum efficiency of the colloidal quantum dot light detection device array of Examples 1-2 and the comparative example is shown.

[0115] According to Figure 3 and Table 1, it can be concluded that the device performance of the comparative example is poorer than that of Examples 1-2, and the external quantum efficiency at 1000-1400 nm is low, because the pure PbS quantum dots used in the comparative example have weak absorption at this place. The organic semiconductor-PbS quantum dot heterojunction of Example 1 still has better absorption and response at 800-1100 nm; the organic semiconductor-PbS quantum dot-organic semiconductor three-layer heterojunction of Example 2 still has better absorption and response at 800-1200 nm. It can be seen that the technical solution of the present application has significant progress.

[0116] Figure 4 Another technical solution of the present application is shown, i.e. the array structure in the case of high-density pixels.

[0117] As shown in Figure 4 the pixel readout circuit composed of thin film transistors (TFT) fabricated on a glass substrate or the pixel readout circuit composed of silicon-based complementary metal oxide semiconductor transistors (MOSFET) on a single-crystal silicon substrate is used as the substrate to meet the imaging requirements of high-density pixels.

[0118] It is apparent for those skilled in the art that the present application is not limited to the details of the above-described exemplary embodiments, but can be implemented in other concrete forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all aspects as illustrative and not restrictive, and the scope of the present application is defined by the appended claims rather than the above description, and it is intended to embrace all changes falling within the meaning and range of equivalents of the claims.

[0119] Furthermore, it should be understood that although the present specification is described in terms of embodiments, not every embodiment exhibits every characteristic or option described in the specification. In addition, it should be understood that although the specification has been described in terms of embodiments, not every embodiment only contains one independent technical solution, and the specification is described in this way only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A quantum dot photodetection device, comprising: The quantum dot light detection device comprises a functional layer, wherein, the functional layer is a multilayer structure, in the multilayer structure, at least a P-type semiconductor layer, a colloidal quantum dot layer and an N-type semiconductor layer are sequentially arranged; the P-type semiconductor layer is selected from one or more of phthalocyanine lead and its derivatives; the colloidal quantum dot layer is selected from one or more of GaP, ZnSe, ZnS, CuO, CuO2, CuS, CuSe, CuInS2, CuInSe2, CuInGaSe, CuInGaS, Ge, PbS, PbSe, HgTe or AgBiS2; the material of the N-type semiconductor layer is selected from one or more of the following structures: ； wherein, the M is selected from the main group elements of I, II, III, IV, or transition elements and their compounds.

2. The quantum dot photodetection device of claim 1, wherein, The thickness of the colloidal quantum dot layer is 10-1000 nm.

3. The quantum dot photodetection device of claim 1, wherein, The thickness of the P-type semiconductor layer is 1-300 nm.

4. The quantum dot photodetection device of claim 1, wherein, The thickness of the N-type semiconductor layer is 1-300 nm.

5. The quantum dot photodetection device of claim 4, wherein, The quantum dot light detection device comprises, from top to bottom or from bottom to top, a bottom electrode, a bottom electrode interface layer, a functional layer, a top electrode interface layer, a top electrode and a packaging layer.

6. The quantum dot photodetection device of claim 5, wherein, The functional layer comprises a P-type semiconductor layer, a colloidal quantum dot layer and an N-type semiconductor layer which are alternately stacked in any order.

7. The quantum dot photodetection device of claim 5, wherein the quantum dot is a core-shell quantum dot. The material of the bottom electrode interface layer and the top electrode interface layer is selected from one or more of metal oxides, metal nitrides, metal sulfides or metal halides.

8. The quantum dot photodetection device of claim 7, wherein, The thickness of the bottom electrode interface layer and the top electrode interface layer is 1-300 nm.

9. A method of fabricating a quantum dot photodetector device as claimed in any one of claims 1-8, characterized in that, It comprises the following steps: (1) substrate cleaning; (2) bottom electrode film formation and ultraviolet irradiation or oxygen plasma cleaning; (3) bottom electrode interface layer film formation preparation; (4) P-type semiconductor layer preparation; (5) colloidal quantum dot layer preparation; (6) N-type semiconductor layer preparation; (7) top electrode interface layer film formation preparation; (8) top electrode preparation; (9) packaging layer preparation.

10. The method for fabricating the quantum dot photodetector according to claim 9, characterized in that, The preparation of the colloidal quantum dot layer comprises the following steps: The preparation of the colloidal quantum dot layer adopts a one-step film formation method after solution phase ligand exchange, or a step-by-step film formation method after solid state ligand exchange.

11. The method of claim 9, wherein the method further comprises: The preparation of the P-type semiconductor layer and the N-type semiconductor layer comprises the following steps: The preparation of the P-type semiconductor layer and the N-type semiconductor layer adopts one or more of solution film formation, vacuum thermal evaporation deposition, magnetron sputtering, atomic layer deposition and chemical vapor deposition.

12. The method of claim 9, wherein the method further comprises: The preparation of the bottom electrode interface layer, the top electrode interface layer, the bottom electrode and the top electrode is independently selected from one or more of solution film formation, sol-gel film formation, vacuum thermal evaporation, atomic layer deposition, chemical vapor deposition, electrodeposition and anodic oxidation.

13. The method of claim 9, wherein the method further comprises: The preparation of the packaging layer is selected from one of vacuum thermal evaporation, chemical vapor deposition, atomic layer deposition, plasma sputtering and liquid film formation.

14. A colloidal quantum dot photodetector array, comprising: The colloidal quantum dot light detection device array is arranged by the quantum dot light detection device of any one of claims 1-8, and sequentially comprises a substrate, a periodically arranged lower electrode array, a lower electrode interface layer, a photosensitive layer, an upper electrode interface layer and a common electrode layer.

15. The colloidal quantum dot photodetector array of claim 14, wherein, The lower electrode interface layer, the photosensitive layer, the upper electrode interface layer and the common electrode layer are all continuous structures in the region of the colloidal quantum dot photodetector.

16. The colloidal quantum dot photodetector array of claim 14, wherein, The lower electrode interface layer, the photosensitive layer, the upper electrode interface layer and the common electrode layer are all not subjected to inter-pixel patterning treatment.

17. The colloidal quantum dot photodetector array of claim 14, wherein, The lower electrode interface layer completely covers the lower electrode array.

18. The colloidal quantum dot photodetector array of claim 14, wherein, The substrate comprises a pixel readout circuit composed of a silicon-based complementary metal-oxide-semiconductor transistor or a thin-film transistor.

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