Photodetector and wearable sensor comprising same

Abstract

The present invention relates to a photodetector and a sensor comprising same. Specifically, according to an embodiment of the present invention, a photodetector may be provided, the photodetector comprising: a positive electrode; a negative electrode facing the positive electrode; a light absorption layer which is located between the positive electrode and the negative electrode and which includes quantum dots so that electron-hole pairs are generated by absorbing light and the generated electron-hole pairs are separated; an electron transport layer which is located between the positive electrode and the light absorption layer and which transports the electrons toward the positive electrode; and a hole transport layer which is located between the light absorption layer and the negative electrode and which transports the holes toward the negative electrode, wherein the quantum dots are heavy metal-free quantum dots in which no heavy metals are included, and the hole transport layer comprises: a first transport layer which is located between the light absorption layer and the negative electrode and which includes a hole migration resistance reducing material so that the holes are extracted from the light absorption layer; and a second transport layer which is located between the first transport layer and the negative electrode and which transports the holes extracted by the first transport layer toward the negative electrode.

Description

Photodetector and wearable sensor including same

[0001] The present invention relates to a photodetector and a sensor including the same.

[0002] A photodetector is a device that detects light. It can detect light by converting absorbed light into electricity. Photodetectors are used in wearable sensors such as photoplethysmography (PPG).

[0003] Conventional photodetectors used in wearable sensors are fabricated based on inorganic thin films, organic semiconductors, or quantum dots. These conventional photodetectors are too thick to be applied to wearable sensors. For example, the light-absorbing layer of a quantum dot-based photodetector must be several hundred nanometers thick to generate photocurrent. Consequently, conventional photodetectors suffer from motion artifacts when applied to wearable sensors.

[0004] Furthermore, conventional photodetectors require an external power source to generate photocurrent, limiting their application to wearable sensors. Furthermore, quantum dot-based photodetectors contain heavy metals such as lead, limiting their application to wearable sensors.

[0005] Embodiments of the present invention have been invented against the background described above, and are intended to provide a photodetector and a wearable sensor including the same, which are environmentally friendly, thin, do not require an external power source, and have excellent detection ability, response rate, and response time.

[0006] According to one aspect of the present invention, a photodetector may include: a positive electrode; a negative electrode facing the positive electrode; a light absorbing layer located between the positive electrode and the negative electrode, the light absorbing layer including quantum dots that absorb light to generate electron-hole pairs and separate the generated electron-hole pairs; an electron transport layer located between the positive electrode and the light absorbing layer and transporting the electrons toward the positive electrode; and a hole transport layer located between the light absorbing layer and the negative electrode and transporting the holes toward the negative electrode, wherein the quantum dots are heavy metal-free quantum dots that do not contain heavy metals, and the hole transport layer may include a first transport layer located between the light absorbing layer and the negative electrode and including a hole movement resistance reducing material so that the holes are extracted from the light absorbing layer; and a second transport layer located between the first transport layer and the negative electrode and transporting the holes extracted by the first transport layer toward the negative electrode.

[0007] In one embodiment, the metal-free quantum dot may include one or more of a group I-III-VI quantum dot, a group III-V quantum dot, and an AgAuSe quantum dot.

[0008] In one embodiment, the group I-III-VI quantum dot may comprise a Cu-In-Se quantum dot, and the group III-V quantum dot may comprise an InAs quantum dot.

[0009] In one embodiment, the metal-free quantum dots can be ligand-exchanged with organic ligands as ions.

[0010] In one embodiment, the first transport layer may further include one or more of a conductive polymer, an oxide, and a conductive organic material.

[0011] In one embodiment, the hole transport resistance reducing material may have ions attached to it as ligands.

[0012] In one embodiment, the conductive polymer comprises PEDOT:PSS, and the hole transport resistance reducing material comprises molybdenum disulfide (MoS2). It may contain nanosheets.

[0013] In one embodiment, the positive electrode may include one or more of a metal, graphene, and MXene.

[0014] In one embodiment, the negative electrode may include one or more of an oxide conductor, silver nanowires, graphene, and MXene.

[0015] In one embodiment, the electron transport layer may comprise one or more of a metal oxide and PCBM ([6,6]-phenyl-C61-butyric acid methyl ester).

[0016] In one embodiment, the second transport layer may include a conductive polymer.

[0017] According to another aspect of the present invention, a wearable sensor may include a photodetector; and a flexible substrate supporting the photodetector.

[0018] In one embodiment, the photodetector may include: a positive electrode; a negative electrode facing the positive electrode; a light absorbing layer positioned between the positive electrode and the negative electrode, the light absorbing layer including quantum dots that absorb light to generate electron-hole pairs and separate the generated electron-hole pairs; an electron transport layer positioned between the positive electrode and the light absorbing layer and transporting the electrons toward the positive electrode; and a hole transport layer positioned between the light absorbing layer and the negative electrode and transporting the holes toward the negative electrode, wherein the quantum dots are heavy metal-free quantum dots that do not include heavy metals, and the hole transport layer may include a first transport layer positioned between the light absorbing layer and the negative electrode and including a hole transport resistance reducing material so that the holes are extracted from the light absorbing layer; and a second transport layer positioned between the first transport layer and the negative electrode and transporting the holes extracted by the first transport layer toward the negative electrode.

[0019] In one embodiment, the flexible substrate may include one or more of parylene, polyethylene naphthalate (PEN), polyethylene terephthalate (PET), and transparent polyimide (TPI).

[0020] According to embodiments of the present invention, there is an effect of providing a photodetector and a wearable sensor including the same, which are environmentally friendly, thin, do not require an external power source, and have excellent detection ability, response rate, and response time.

[0021] FIG. 1 is a drawing showing a photodetector and a wearable sensor including the same according to one embodiment of the present invention.

[0022] FIG. 2 is a drawing showing the configuration of a photodetector according to one embodiment of the present invention.

[0023] FIG. 3 is a transmission electron microscope photograph showing a cross-section of a photodetector according to one embodiment of the present invention.

[0024] FIG. 4 is a diagram showing the energy levels of a photodetector according to one embodiment of the present invention.

[0025] FIG. 5 is a diagram showing that an organic ligand is exchanged into an ion by a ligand exchange reaction in a metal-free quantum dot of a photodetector according to one embodiment of the present invention.

[0026] Figure 6 is a diagram showing the absorption, Mott-Schottky diagram, and changes in the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) as a function of the wavelength of light of heavy metal-free quantum dots that are ligand-exchanged with organic ligands and heavy metal-free quantum dots that are not ligand-exchanged.

[0027] FIG. 7 is a drawing showing a method for manufacturing a light detector according to one embodiment of the present invention.

[0028] Figure 8 is a graph showing space-charge-limited current (SCLC) test curves of a hole transport layer without a hole transport resistance reducing material and a hole transport layer with a hole transport resistance reducing material.

[0029] FIG. 9 is a graph showing the electrochemical impedance spectroscopy (EIS) Nyquist diagram of a photodetector in which the hole transport layer does not include a hole transport resistance reducing material and a photodetector according to one embodiment of the present invention in which the hole transport layer includes a hole transport resistance reducing material.

[0030] FIG. 10 is a graph showing a current density versus voltage curve (JV curve), response and detectivity according to the wavelength of light of a photodetector according to an embodiment of the present invention, in which the hole transport layer does not include a hole transport resistance reducing material and the hole transport layer includes a hole transport resistance reducing material.

[0031] FIG. 11 is a graph showing the linear dynamic range (LDR), the ratio of photocurrent to dark current according to light intensity, and the external quantum efficiency according to the wavelength of light of a photodetector according to an embodiment of the present invention in which the hole transport layer does not include a hole transport resistance reducing material and the hole transport layer includes a hole transport resistance reducing material.

[0032] FIG. 12 is a graph showing the response time of a photodetector according to an embodiment of the present invention in which the hole transport layer does not include a hole transport resistance reducing material and in which the hole transport layer includes a hole transport resistance reducing material.

[0033] FIG. 13 is a drawing showing a wearable sensor according to one embodiment of the present invention applied to a photoplethysmography sensor.

[0034] FIG. 14 is a diagram showing the response, external quantum efficiency, and detectability according to the wavelength of light of a photoplethysmography sensor using a wearable sensor according to one embodiment of the present invention.

[0035] FIG. 15 is a graph showing normalized photocurrent according to the bending radius and normalized photocurrent according to the number of bends of a photoplethysmography sensor using a wearable sensor according to one embodiment of the present invention.

[0036] Figure 16 is a graph showing pulse measurement using a conventional photoplethysmography sensor and a photoplethysmography sensor using a wearable sensor according to one embodiment of the present invention.

[0037] Figure 17 is a graph showing pulse measured at rest, during exercise, and at rest after exercise using a photoplethysmography sensor that uses a wearable sensor according to one embodiment of the present invention.

[0038] Hereinafter, specific embodiments for implementing the technical idea of ​​the present invention will be described in detail with reference to the drawings.

[0039] In addition, when explaining the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description is omitted.

[0040] Additionally, when it is said that a component is 'connected to', 'supported by', or 'transmitted to' another component, it should be understood that it may be directly connected to, supported by, or transmitted to that other component, but there may also be other components present in between.

[0041] The terminology used herein is intended solely to describe specific embodiments and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0042] Additionally, some components in the attached drawings are exaggerated, omitted, or schematically illustrated, and the size of each component does not entirely reflect the actual size.

[0043] Additionally, terms that include ordinal numbers, such as "first," "second," etc., may be used to describe various components, but these components are not limited by such terms. These terms are used solely to distinguish one component from another.

[0044] The term "comprising" as used in the specification means specifying a particular characteristic, region, integer, step, operation, element and / or component, but does not exclude the presence or addition of other particular characteristics, regions, integers, steps, operations, elements, components and / or groups.

[0045] In the specifications and drawings, cases where a hole transport resistance reducing material is included are indicated as 'hybrid', and cases where it is not included are indicated as 'pristine', and in some cases, English abbreviations are used for convenience of explanation.

[0046] Hereinafter, with reference to FIGS. 1 to 17, a specific configuration of a photodetector and a wearable sensor including the same according to an embodiment of the present invention will be described. A wearable sensor (1) can be worn by a person to measure a biosignal. For example, the wearable sensor (1) may be a photoplethysmography (PPG) sensor that measures pulse. The wearable sensor (1) may include a photodetector (10), a flexible substrate (20), a light source (30), a detector connection terminal (40), and a light source connection terminal (50).

[0047] Referring to FIGS. 2 to 4, a photodetector (10) can detect light. The photodetector (10) can detect light by converting absorbed light into electricity. The photodetector (10) absorbs light to generate electron-hole pairs, separates the generated electrons and holes, and transports the separated electrons and holes to generate electricity. The photodetector (10) can include a positive electrode (100), a negative electrode (200), a light absorbing layer (300), an electron transport layer (ETL, electron transport layer) (400), and a hole transport layer (HTL, hole transport layer) (500).

[0048] In the positive electrode (100), electrons generated and separated in the light absorbing layer (300) can be transported through the electron transport layer (400). The positive electrode (100) can include one or more of a metal, graphene, and MXene. The metal included in the positive electrode (100) can include silver (Ag). For example, the positive electrode (100) can include silver nanowires. The positive electrode (100) can reflect light. The light reflected from the positive electrode (100) can be absorbed in the light absorbing layer (300). The positive electrode (100) can be connected to an electrical measuring device (not shown), such as an oscilloscope, via a detector connection terminal (40).

[0049] In the negative electrode (200), holes generated and separated in the light absorbing layer (300) can be transported through the electron transport layer (400). The negative electrode (200) can include one or more of an oxide conductor, silver nanowires, graphene, and MXene. The oxide conductor included in the negative electrode (200) can include indium tin oxide (ITO). The negative electrode (200) can transmit light. Light transmitted through the negative electrode (200) can be absorbed in the light absorbing layer (300). The negative electrode (200) can face the positive electrode (100).

[0050] In the light absorbing layer (300), light is absorbed to generate electron-hole pairs, and the generated electron-hole pairs can be separated. The light absorbing layer (300) may include quantum dots (QDs). Quantum dots are semiconductor crystals with a size of several nanometers, and are an optoelectronic material having a quantum confinement effect in which the bandgap of the material changes depending on the size of the crystal. When light is absorbed by the quantum dots, electron-hole pairs can be generated. The generated electron-hole pairs can be separated by an electric field generated by the quantum dots. The light absorbing layer (300) may be located between the positive electrode (100) and the negative electrode (200).

[0051] The quantum dots included in the light absorbing layer (300) may be heavy metal-free quantum dots that do not contain heavy metals. Since the heavy metal-free quantum dots do not contain heavy metals harmful to the human body, the photodetector (10) can be used as a wearable sensor (1). The heavy metal-free quantum dots may include one or more of group I-III-VI quantum dots, group III-V quantum dots, and AgAuSe quantum dots. The group I-III-VI quantum dots may include Cu-In-Se quantum dots (CISe QDs). Additionally, the group III-V quantum dots may include InAs quantum dots.

[0052] Cu-In-Se quantum dots can be synthesized using the reaction of a metal halide-oleylamine (OAm) complex and oleylammonium selenocarbamate as follows. First, the oleylammonium selenocarbamate precursor can be obtained by bubbling carbon monoxide (CO) gas into 10.0 mL of oleylamine containing selenium (Se) powder until the precursor becomes clear and colorless. Copper iodide (CuI (0.5 mmol)), indium triiodide (InI3 (0.5 mmol)), and oleylamine (15.0 mL) are mixed in a 50.0 mL three-necked flask in a glove box, heated to 120°C for 30 minutes under vacuum, and then cooled to 70°C in an argon (Ar) atmosphere. Oleylammonium selenocarbamate precursor (2.0 mL) is rapidly injected into the metal halide-oleylamine complex precursor solution under a constant argon (Ar) flow. The mixed solution is then heated to 190°C and maintained at 190°C for 20 min. After the reaction, the synthesized Cu-In-Se quantum dots are precipitated by adding ethanol containing 0.5 mL of tri-n-octylphosphine (TOP) and 0.1 mL of oleic acid (OA), and centrifuged. The supernatant is discarded, and Cu-In-Se quantum dots (CISe QDs) are precipitated again through ethanol and subsequent centrifugation. Finally, the Cu-In-Se quantum dots (CISe QDs) are dispersed in toluene and filtered through a 0.2 μm polytetrafluoroethylene (PTFE) filter for further analysis.

[0053] Referring to Figure 5, the heavy metal-free quantum dots can be ligand-exchanged with organic ligands. In the case of Cu-In-Se quantum dots, tetrabutylammonium iodide (TBAI) is used to exchange the organic ligand, oleylamine, with iodide ions (I - ) can be ligand exchanged. The ligand exchange of Cu-In-Se quantum dots can be performed as follows. First, ethanol (10 mg mL) is added to the organic ligand capping film of Cu-In-Se quantum dots. -1 ) can be added for 60 seconds to complete the ligand exchange. In addition, the ligand-exchanged quantum dot thin film can be cleaned by spin-coating pure ethanol at 2,000 rpm for 15 seconds to remove excess TBAI. Iodine ions (I - ) ligand-exchanged Cu-In-Se quantum dots were denoted as TBAI-QDs, and iodine ions (I - ) before ligand exchange can be denoted as OAm-QDs.

[0054] Referring to Fig. 6, after ligand exchange, the absorption spectrum shows that the band edge transition position shifts to a longer wavelength (800 to 830 nm), which corresponds to an optical band gap (Eg) of 1.41 to 1.36 eV. In addition, since a surface dipole is formed in the TBAI ligand, the valence band maximum (VBM) of the ligand-exchanged metal-free quantum dots is slightly higher than that of the non-ligand-exchanged metal-free quantum dots, which is advantageous for hole transport between the metal-free quantum dots and the hole transport layer (500). In addition, Mott-Schottky (MS) analysis showed that the carrier concentration of the film increased after ligand exchange.

[0055] The electron transport layer (400) can transport electrons separated from the light absorbing layer (300) toward the positive electrode (100). The electron transport layer (400) can include at least one of a metal oxide and PCBM ([6,6]-phenyl-C61-butyric acid methyl ester). The metal oxide can include at least one of titanium oxide (TiO2) and zinc oxide (ZnO). The metal oxide can include zinc oxide (ZnO) nanoparticles. The electron transport layer (400) can be located between the positive electrode (100) and the light absorbing layer (300).

[0056] Zinc oxide nanoparticles can be synthesized as follows. First, 0.1 mol of zinc acetate dihydrate (ZnAc22H2O) dissolved in 30.0 mL of dimethyl sulfoxide (DMSO) is stirred at 30°C for 1 h. 0.5 mol of tetramethylammonium hydroxide pentahydrate (TMAH) dissolved in 10.0 mL of anhydrous ethanol (EtOH) is added dropwise to the zinc acetate precursor at a rate of 0.5 mL min-1 while stirring vigorously at 30°C for 1 h. The synthesized zinc oxide nanoparticles are washed with ethyl acetate (EA) and centrifuged at 8,000 g for 5 min. Zinc oxide nanoparticles are dispersed in 1-butanol (BuOH, 1-butanol) in a glove box and used for the electron transport layer (400) of the photodetector (10).

[0057] The hole transport layer (500) can transport holes separated from the light absorbing layer (300) toward the negative electrode (200). The hole transport layer (500) can be positioned between the light absorbing layer (300) and the negative electrode (200). The hole transport layer (500) can include a first transport layer (510) and a second transport layer (520).

[0058] The first transport layer (510) can extract holes from the light absorbing layer (300). The first transport layer (510) can include at least one of a conductive polymer, an oxide, and a conductive organic material, and a hole transport resistance reducing material. Since the hole transport resistance reducing material is included in the first transport layer (510), hole extraction from the light absorbing layer (300) can be facilitated. The first transport layer (510) can be positioned between the light absorbing layer (300) and the negative electrode (200).

[0059] The conductive polymer may include PEDOT:PSS. PEDOT is poly(3,4-ethylenedioxythiophene). PSS is poly(styrenesulfonate).

[0060] The oxide may include one or more of nickel oxide (NiOx) and molybdenum oxide (MoOx).

[0061] The conductive organic material may include at least one of TAPC (1,1-Bis[(di-4-tolylamino)phenyl]cyclohexane) and HAT-CN (hexa-azatriphenylene hexacarbonitrile).

[0062] The hole transport resistance reducing material is molybdenum disulfide (MoS2). Nanosheets can be included. Molybdenum disulfide nanosheets can be synthesized as follows. 5.0 mL of oleylamine is placed in a 50.0-mL three-necked flask and heated to 320°C. Then, 0.675 mmol of molybdenum chloride (MoCl5) in 0.75 mL of oleic acid and 5.0 mL of oleylamine are degassed at 120°C for 30 minutes. After cooling the mixture to 40°C, 0.2 mL of carbon disulfide (CS2) is injected. The precursor solution is placed in a syringe and slowly injected into the oleylamine solution over 30 minutes. After injection, the reaction mixture is maintained at 320°C for an additional 90 minutes. Molybdenum disulfide is precipitated by adding 1-butanol and 3.0 mL of tri-n-octylphosphine, and centrifuged at 10,000 g for 5 minutes to remove excess carbon disulfide. The molybdenum disulfide is then washed three times with hot ethanol, centrifuged at 8,000 g for 5 minutes, and dispersed in chloroform in a glove box.

[0063] The hole transport resistance reducing material can be attached to ions as ligands. When the hole transport resistance reducing material includes molybdenum disulfide nanosheets, iodine ions (I) are used using tetrabutylammonium iodide (TBAI). - ) can be attached to molybdenum disulfide nanosheets as a ligand. When the hole transport resistance reducing material is molybdenum disulfide, attachment of iodine ions as a ligand to molybdenum disulfide nanosheets can be performed as follows. First, ligand exchange can be completed by adding a TBAI solution in ethanol to the molybdenum disulfide nanosheets for 60 seconds. In addition, by performing spin coating twice with pure ethanol at 2,000 rpm for 15 seconds on the molybdenum disulfide nanosheets on which ligand exchange has been completed, excess TBAI can be removed.

[0064] The second transport layer (520) can transport the holes extracted by the first transport layer (510) toward the negative electrode (200). The second transport layer (520) can include a conductive polymer. The conductive polymer can include PEDOT:PSS. The second transport layer (520) can be positioned between the first transport layer (510) and the negative electrode (200).

[0065] Referring to FIG. 7, the photodetector (10) may have a configuration of ITO / HTL / TBAI-QDs / ZnO / Ag and may be manufactured as follows. An indium tin oxide (ITO) substrate is ultrasonically cleaned with detergent, acetone, and ethanol for 15 minutes each. The cleaned ITO substrate is dried with argon flow and then treated with ultraviolet / ozone for 10 minutes. A PEDOT:PSS film is spin-coated twice on the ITO at 3,000 rpm for 30 seconds and then annealed on a hot plate at 120°C for 20 minutes. A PEDOT:PSS film is spin-coated once on the ITO at 3,000 rpm for 30 seconds and then annealed on a hot plate at 120°C for 20 minutes. MoS2 is introduced by spin-coating molybdenum disulfide (MoS2) nanosheets and repeating the solid ligand exchange process (typically 4 cycles). PEDOT:PSS is then spin-coated on the TBAI-loaded MoS2 with the same spin-coating parameters as the bottom PEDOT:PSS to form a PEDOT:PSS:MoS2 film. The final amount of MoS2 nanosheets in the hole transport layer (HTL) can be controlled by adjusting the concentration of the MoS2 solution and the number of cycles of MoS2 spin-coating. Cu-In-Se quantum dot (CISe QD) solution is spin-coated at 2,000 rpm for 15 s, followed by TBAI-ligand exchange and annealing at 120°C for 10 min. The thickness of the quantum dot (QD) film is controlled by repeating the deposition process (typically 7 cycles). A zinc oxide (ZnO) solution is spin-coated at 2,000 rpm for 15 seconds and then annealed at 120°C for 10 minutes. Finally, a 90 nm silver (Ag) electrode is thermally evaporated at a rate of 1 Å with an effective area of ​​1 Å to deposit on the ZnO layer.

[0066] Referring to Fig. 8, the space-charge-limited current (SCLC) test in the case of only having a hole transport layer (500) having a configuration of ITO / HTL / TBAI-QD / Ag shows that the electrical characteristics are improved when a hole transport resistance reducing material is included. The estimated trap density (n) of Cu-In-Se quantum dots in the case where the hole transport layer (500) does not include a hole transport resistance reducing material trap ) is 1.68×10 16 cm -3 In addition, the estimated trap density of Cu-In-Se quantum dots when the hole transport layer (500) includes a hole transport resistance reducing material is 2.87×10 15 cm -3 In addition, the hole mobility (μ) of Cu-In-Se quantum dots when the hole transport layer (500) includes a hole transport resistance reducing material h ) is 7.94×10 -4 cm 2 V -1 s -1 It can be seen that the hole transport layer (500) is improved by 94% compared to the case where the hole transport layer does not include a hole transport resistance reducing material.

[0067] Table 1 below shows the values ​​of the electrochemical impedance spectroscopy (EIS) parameters of the photodetector (10) when the hole transport layer (500) does not include a hole transport resistance reducing material (Pristine HTL) and when the hole transport layer (500) includes a hole transport resistance reducing material (Hybrid HTL).

[0068]

[0069] Here, R s is the series resistance, R ct1 is the interface resistance, R ct2 Is It is the charge transfer resistance.

[0070] Referring to FIG. 9 and Table 1, the photodetector (10) in which the hole transport layer (500) does not include a hole transport resistance reducing material and in which the hole transport layer (500) includes a hole transport resistance reducing material has a series resistance (R s ) and interface resistance (R ct1 ) there is no significant difference. However, the charge transfer resistance (R) of the photodetector (10) when the hole transport layer (500) includes a hole transport resistance reducing material ct2 ) is 87.2 kΩ, and the charge transfer resistance (R ct2 ) is only 63% of the case where the hole transport resistance reducing material of 139 kΩ is not included. This is because when the hole transport resistance reducing material is included in the hole transport layer (500), the recombination of electrons and holes is suppressed.

[0071] Referring to FIG. 10, the photocurrent density (J) of the photodetector (10) when the hole transport layer (500) includes a hole transport resistance reducing material light ) and dark current density (J dark ) are more than 5 times higher than the photocurrent density of the photodetector (10) without external power at 0 V bias and 10 times lower than the dark current density. This is because charge injection through a strong potential barrier is suppressed due to the fast charge extraction and enhanced photovoltage possible by the hole transport layer (500) including the hole transport resistance reducing material. In addition, the deviation of the origin and J light The asymmetry of the -V curve indicates the presence of a built-in electric field. The photodetector (10) in which the hole transport layer (500) does not include a hole transport resistance reducing material has the highest J at an external voltage of 0 V. light / J dark This ratio indicates that the device can operate efficiently without an external power source. Operating without an external voltage effectively limits dark current while minimizing energy consumption. In other words, the photodetector (10) can be used without a power source.

[0072] In addition, the photodetector (10) in which the hole transport layer (500) includes a hole transport resistance reducing material also exhibits a wide spectrum photoresponse from the ultraviolet (250 nm) to the near-infrared region (1,050 nm).

[0073] In addition, the responsivity (R) of the photodetector (10) when the hole transport layer (500) includes a hole transport resistance reducing material is 87.9 mA W at 470 nm light. -1 , otherwise 38.3mA W -1 See 2 It's more than a ship.

[0074] In addition, the detectivity (D*) of the photodetector (10) when the hole transport layer (500) includes a hole transport resistance reducing material is 10 across the visible range. 12 Jones, and up to 2.10 x 10 at a wavelength of light of 470 nm. 12 Jones. This value is 2.63 x 10, which is the detection capability of the photodetector (10) when the hole transport layer (500) does not include a hole transport resistance reducing material. 11 (Jones) is considerably higher.

[0075] Referring to Fig. 11, when the wavelength of light is 555 nm and there is no external voltage, the photocurrent density of the photodetector (10) when the hole transport layer (500) includes a hole transport resistance reducing material increases to 4.57×10 as the light intensity increases. -8 5.82×10 in -3 A cm -2 increases linearly. However, the photocurrent density of the photodetector when the hole transport layer (500) does not include a hole transport resistance reducing material increases to 8.74×10 as the light intensity increases. -7 2.81×10 in -3 A cm -2 It increases linearly.

[0076] In addition, the photodetector in which the hole transport layer (500) does not include a hole transport resistance reducing material has a linear dynamic range (LDR) of 70 dB and a sensitivity of 1.36×10 4 (163.0 mW cm -2 I of light / I dark shows the ratio. However, the photodetector (10) in which the hole transport layer (500) includes a hole transport resistance reducing material has an LDR of 102 dB and an RDR of 1.31×10 5 (163.0 mW cm -2 I of light / I dark Shows the ratio.

[0077] In addition, the external quantum efficiency (EQE) of the photodetector (10) when the hole transport layer (500) includes a hole transport resistance reducing material is 23.2% at 470 nm light, which is 10.1% of the case when it does not. It's more than a ship.

[0078] Referring to FIG. 12, the rise / decay time (τ) of the photodetector when the hole transport layer (500) does not include a hole transport resistance reducing material rise / τ decay ) is 0.82 / 1.55 ​​ms. In addition, the rise / decrease time of the photodetector (10) when the hole transport layer (500) includes a hole transport resistance reducing material is 0.64 / 1.00 ms. The faster rise / decrease time of the photodetector (10) when the hole transport layer (500) includes a hole transport resistance reducing material is due to the rapid separation of electron-hole pairs by the built-in electric field and the high hole extraction efficiency. The fast response of the photodetector (10) makes it suitable for real-time medical monitoring.

[0079] Again, referring to FIG. 1, the flexible substrate (20) can support the photodetector (10). The photodetector (10) is manufactured on the flexible substrate (20), and the flexible substrate (20) can support the photodetector (10). The flexible substrate (20) can include one or more of parylene, polyethylene naphthalate (PEN), polyethylene terephthalate (PET), and transparent polyimide (TPI).

[0080] The light source (30) can emit light. For example, the wearable sensor (1) may include a light source (30) applied to a photoplethysmography (PPG) sensor. However, the wearable sensor (1) may include a different configuration when applied to other sensors. The light source (30) may be a light emitting diode (LED). The light source (30) may be supported by a flexible substrate (20). When the light source (30) is manufactured on the flexible substrate (20), the flexible substrate (20) may support the light source (30).

[0081] The detector connection terminal (40) can be connected to the photodetector (10). In addition, the detector connection terminal (40) can be connected to an electrical measuring device such as an oscilloscope. By connecting the photodetector (10) of the detector connection terminal (40) and the electrical measuring device, the electric current or voltage generated according to the light absorbed by the photodetector (10) can be measured. There may be a plurality of detector connection terminals (40). Any one of the plurality of detector connection terminals (40) can be connected to the positive electrode (100) of the photodetector (10) and the electrical measuring device such as an oscilloscope. Another one of the plurality of detector connection terminals (40) can be connected to the negative electrode (200) of the photodetector (10) and the electrical measuring device. The detector connection terminal (40) can be supported by the flexible substrate (20). A detector connection terminal (40) is manufactured on a flexible substrate (20), and the flexible substrate (20) can support the detector connection terminal (40). The detector connection terminal (40) can include one or more of copper wire, copper film, copper tape, gold, silver, aluminum, and an anisotropic conductive film (ACF).

[0082] The light source connection terminal (50) can be connected to the light source (30). In addition, the light source connection terminal (50) can be connected to a power source. By connecting the light source (30) of the light source connection terminal (50) to the power source, light can be emitted from the light source (30). There may be a plurality of light source connection terminals (50). One of the plurality of light source connection terminals (50) can be connected to the positive pole of the light source (30) and the positive pole of the power source. Another of the plurality of light source connection terminals (50) can be connected to the negative pole of the light source (30) and the negative pole of the power source. The light source connection terminal (50) can be supported by the flexible substrate (20). The light source connection terminal (50) is manufactured on the flexible substrate (20), and the flexible substrate (20) can support the light source connection terminal (50).

[0083] Referring to Fig. 13, a wearable sensor (1) according to one embodiment of the present invention is applied to a photoplethysmography sensor. The photoplethysmography sensor has a configuration of Ecoflex / micro-LED / Cu / PEN / epoxy / Cr / Au / ITO / HTL / TBAI-QDs / ZnO / Ag / perylene and can be manufactured as follows.

[0084] For easy handling of the ultra-thin photoplethysmography sensor, a glass substrate coated with polydimethylsiloxane (PDMS) is used as a supporting substrate. A PEN film (12 μm thick) is attached on the supporting substrate, and 500 nm thick epoxy is spin-coated. Chromium (Cr) (5 nm) and gold (Au) (30 nm) are used for interconnection at a thickness of 0.5 Å s. -1 Sequential thermal evaporation is performed at a rate of . After that, indium tin oxide (ITO) is deposited by sputtering as a transparent electrode. After cleaning the sample, a photodetector (10) is fabricated through the same procedure as for a rigid substrate. Then, 1 μm thick perylene-C is deposited for encapsulation. To fabricate an LED component, the PEN film containing the photodetector (10) is peeled off from the supporting substrate. On the opposite side of the PEN film, 1.5 Å s is applied for interconnection. -1 Copper (Cu) (200 nm) is deposited at a rate of . Then, a red micro LED (wavelength: 624 nm) is attached with silver paste. Finally, the LED is coated with Ecoflex for encapsulation.

[0085] Referring to Fig. 14, the parylene and PEN included in the flexible substrate (20) have excellent mechanical properties, high transparency, and a high processing temperature (150°C or higher). The photodetector (10) of the wearable sensor (1) applied to the photoplethysmography sensor shows excellent performance. The detection ability of the photodetector (10) under the condition of light with a wavelength of 470 nm and no external voltage is 1.30×10 when the flexible substrate (20) includes parylene. 12 Jones, and if PEN is included, 1.19×10 12 It's Jones.

[0086] Referring to Fig. 15, the photodetector (10) of the wearable sensor (1) applied to the photoplethysmography sensor shows mechanical and optoelectrical reliability at various bending radii ranging from 0.5 to 18 mm.

[0087] Additionally, it shows that the initial performance is maintained even after 1,000 cycles of bending tests.

[0088] Referring to FIG. 16, compared to a conventional photoplethysmography sensor, a photoplethysmography sensor to which a wearable sensor (1) according to an embodiment of the present invention is applied can detect the discrete difference between a systolic peak and a diastolic peak without noise.

[0089] Referring to FIG. 17, the photoplethysmography sensor to which the wearable sensor (1) according to one embodiment of the present invention is applied shows that it can monitor real-time biosignals under various activity conditions. Since the photoplethysmography sensor to which the wearable sensor (1) according to one embodiment of the present invention is applied is attached to the fingertip in a conformal manner through viscoelastic echoflex encapsulation, it can obtain precise and accurate photoplethysmography signals without motion artifacts. The photoplethysmography sensor to which the wearable sensor (1) according to one embodiment of the present invention is applied is suitable for long-term use without causing discomfort and can measure heart rate under various conditions. Therefore, it can be used in various non-invasive biosignal monitoring devices.

[0090] Although the embodiments of the present invention have been described as specific embodiments, these are merely examples, and the present invention is not limited thereto, but should be construed to have the broadest scope in accordance with the technical concepts disclosed in this specification. Those skilled in the art may implement patterns of shapes not specified by combining / substituting the disclosed embodiments, but this also does not depart from the scope of the present invention. In addition, those skilled in the art may easily modify or alter the disclosed embodiments based on this specification, and it is clear that such modifications or alterations also fall within the scope of the present invention.

[0091]

[0092] 1: Wearable sensor 10: Photodetector

[0093] 20: Flexible substrate 30: Light source

[0094] 40: Detector connection terminal 50: Light source connection terminal 100: Positive electrode 200: Negative electrode

[0095] 300: Light absorbing layer 400: Electron transport layer

[0096] 500: hole transport layer 510: first transport layer

[0097] 520: Second transport layer

Claims

1. Positive electrode; A negative electrode facing the positive electrode; A light absorbing layer including quantum dots, positioned between the positive electrode and the negative electrode, which absorbs light to generate electron-hole pairs and separates the generated electron-hole pairs; An electron transport layer positioned between the positive electrode and the light absorbing layer, and transporting the electrons in the direction of the positive electrode; and A hole transport layer positioned between the light absorbing layer and the negative electrode, and transporting the holes toward the negative electrode, The above quantum dots are heavy metal-free quantum dots that do not contain heavy metals, The above hole transport layer is, A first transport layer positioned between the light absorbing layer and the negative electrode, the first transport layer including a hole transport resistance reducing material so that the holes are extracted from the light absorbing layer; and A second transport layer positioned between the first transport layer and the negative electrode, and transporting the holes extracted by the first transport layer toward the negative electrode, Photodetector.

2. In paragraph 1, The above heavy metal-free quantum dot comprises at least one of group I-III-VI quantum dots, group III-V quantum dots, and AgAuSe quantum dots. Photodetector.

3. In paragraph 2, The above group I-III-VI quantum dots include Cu-In-Se quantum dots, The above III-V group quantum dots include InAs quantum dots, Photodetector.

4. In paragraph 1, The above heavy metal-free quantum dots are ligand-exchanged with organic ligands as ions. Photodetector.

5. In paragraph 1, The above first transport layer is, Further comprising at least one of a conductive polymer, an oxide, and a conductive organic material. Photodetector.

6. In paragraph 5, The above hole transport resistance reducing material is one in which ions are attached as ligands. Photodetector.

7. In paragraph 6, The above conductive polymer is, Contains PEDOT:PSS, The above hole transport resistance reducing material is molybdenum disulfide (MoS2). Containing nanosheets, Photodetector.

8. In paragraph 1, The above two electrodes include at least one of metal, graphene, and MXene. Photodetector.

9. In paragraph 1, The above negative electrode comprises at least one of an oxide conductor, silver nanowire, graphene, and MXene. Photodetector.

10. In paragraph 1, The electron transport layer comprises at least one of a metal oxide and PCBM ([6,6]-phenyl-C61-butyric acid methyl ester). Photodetector.

11. In paragraph 1, The second transport layer is, Containing a conductive polymer, Photodetector.

12. Photodetector; and Including a flexible substrate supporting the above photodetector, Wearable sensors.

13. In paragraph 12, The above photodetector, positive electrode; A negative electrode facing the positive electrode; A light absorbing layer including quantum dots, positioned between the positive electrode and the negative electrode, which absorbs light to generate electron-hole pairs and separates the generated electron-hole pairs; An electron transport layer positioned between the positive electrode and the light absorbing layer, and transporting the electrons in the direction of the positive electrode; and A hole transport layer positioned between the light absorbing layer and the negative electrode, and transporting the holes toward the negative electrode, The above quantum dots are heavy metal-free quantum dots that do not contain heavy metals, The above hole transport layer is, A first transport layer positioned between the light absorbing layer and the negative electrode, the first transport layer including a hole transport resistance reducing material so that the holes are extracted from the light absorbing layer; and A second transport layer positioned between the first transport layer and the negative electrode, and transporting the holes extracted by the first transport layer toward the negative electrode, Wearable sensors.

14. In paragraph 13, The flexible substrate comprises at least one of parylene, polyethylene naphthalate (PEN), polyethylene terephthalate (PET), and transparent polyimide (TPI). Wearable sensors.

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