Method of manufacturing an optoelectronic device

Abstract

Method for manufacturing an optoelectronic device The present description relates to a method for manufacturing an optoelectronic device (100), such as a photodetector or an imager, comprising a substrate (110) covered by a stack of active layers, the method comprising the formation of an encapsulation element on the stack of layers according to the following steps: - depositing a first full-plate inorganic layer (170), - locally forming an organic buffer layer (180) on the first inorganic layer (170), a first portion of the first inorganic layer (170) facing the stack of active layers being covered by the organic buffer layer (180) and a second portion of the first inorganic layer (170) not being covered by the organic buffer layer (180), - etching the second portion of the first inorganic layer (170), by wet etching,- forming a second inorganic layer (190) on the organic buffer layer (180). Figure for abstract: Fig. 1E,

Description

Title of the invention: Method for manufacturing an optoelectronic device Technical field

[0001] The present description relates generally to optoelectronic devices comprising organic photodiode optical sensors or organic light-emitting diode display pixels and their manufacturing methods. Prior art

[0002] Many techniques for integrating optical sensors under a transparent screen are known, for example for the integration of a fingerprint sensor in a mobile phone or for the integration of optical sensors in a screen of a mobile phone for facial recognition, or for medical applications.

[0003] An organic optoelectronic device generally comprises a stack of organic active layers. The stack comprises an active organic semiconductor layer (OSC) which is the area of ​​the optoelectronic device in which the majority of the radiation of interest is captured by the optoelectronic device. This organic layer is disposed between an electron injection layer (EIL) and a hole injection layer (HIL).

[0004] All of these layers are, conventionally, protected by an encapsulation element which may comprise an organic buffer layer and an inorganic layer. Such an encapsulation element may be formed according to the following steps: - deposition of the organic buffer layer on the HIL layer and structuring by photolithography, - deposition and structuring of a resin by photolithography to structure the inorganic encapsulation layer, - full plate deposition of the inorganic layer, - release of the contacts by removing the resin covered with the inorganic layer ('Lift-off').

[0005] However, the solvents used to form the organic buffer layer and / or the solvents used for the development and removal ('stripping') of the resins can deteriorate the organic active layers and therefore reduce the performance of the optoelectronic device. Summary of the invention

[0006] An object of an embodiment is to provide a method of manufacturing an optoelectronic device making it possible to prevent deterioration of the or- organic.

[0007] This aim is achieved by a method of manufacturing an optoelectronic device, such as a photodetector or an imager, comprising a substrate covered by a stack of active layers comprising an electron injection layer, an organic semiconductor layer, a hole injection layer, the method comprising forming an encapsulation element on the stack of active layers according to the following steps: - deposit a first inorganic layer on a full plate, - forming an organic buffer layer on the first inorganic layer, a first part of the first inorganic layer facing the stack of active layers being covered by the organic buffer layer and a second part of the first inorganic layer not being covered by the organic buffer layer, - etch the second part of the first inorganic layer not covered by the organic buffer layer, by wet etching, - form a second inorganic layer on the organic buffer layer.

[0008] According to a particular embodiment, the first inorganic layer and / or the second inorganic layer are made of a material chosen from oxides such as alumina, titanium oxide, zirconium oxide, silicon oxide, magnesium oxide and nitrides, for example silicon nitride.

[0009] According to a particular embodiment, the first inorganic layer and / or the second inorganic layer are deposited by atomic layer deposition.

[0010] According to a particular embodiment, the first inorganic layer and / or the second inorganic layer are made of alumina.

[0011] According to a particular embodiment, the first inorganic layer has a thickness of between 3 and 25 nm.

[0012] According to a particular embodiment, the substrate comprises a first electrode and a second electrode covered by and in contact with at least one of the layers of the stack of active layers and contact pads offset and connected, respectively, to the first electrode and to the second electrodes, the first inorganic layer covering the contact pads during its full-plate deposition, the etching step leading to the release of the contact pads.

[0013] The invention also relates to an optoelectronic device, such as a photodetector or an imager, comprising a substrate covered by a stack of active layers comprising an electron injection layer, an organic semiconductor layer, a hole injection layer, the stack being protected by an encapsulation element comprising a first inorganic layer, an organic buffer layer and a second inorganic layer.

[0014] According to a particular embodiment, the first inorganic layer is made of a material chosen from oxides such as alumina, titanium oxide, zirconium oxide, and nitrides, for example silicon nitride.

[0015] According to a particular embodiment, the first inorganic layer has a thickness of between 3 and 25 nm.

[0016] According to a particular embodiment, the first inorganic layer is made of alumina. Brief description of the drawings

[0017] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0018] [Fig.lA], [Fig.lB], [Fig.lC], [Fig.lD] and [Fig.lE] schematically represent different steps of a method of manufacturing an optoelectronic device according to a particular embodiment; and

[0019] [Fig.2] is a graph representing current-voltage curves obtained after thermal aging of an optoelectronic device whose encapsulation element is formed by a first inorganic layer, an organic buffer layer and a second inorganic layer according to a particular embodiment (curve with cross), as well as for comparison of an optoelectronic device whose encapsulation element is formed by an organic buffer layer and a second inorganic layer (curve without cross).

[0020] The various elements are not represented on a uniform scale in order to facilitate understanding of the figures. Description of the embodiments

[0021] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0022] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed.

[0023] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0024] In the following description, when referring to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made unless otherwise specified to the orientation of the figures.

[0025] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

[0026] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed.

[0027] In particular, the operation of a display screen and an image sensor has not been detailed, the embodiments described being compatible with conventional display screens and image sensors. In addition, the other components of the optoelectronic device incorporating a display screen or an image sensor have also not been detailed, the embodiments described being compatible with the other conventional components of optoelectronic devices with a display screen and / or an image sensor.

[0028] Further, the terms "insulator" and "conductor" are herein considered to mean "electrically insulating" and "electrically conducting," respectively.

[0029] Furthermore, the term "radiation of interest" refers to the radiation that is to be captured or emitted by an optoelectronic device. For example, the radiation of interest may comprise the visible spectrum and the near infrared, i.e. the wavelengths between 400 nm and 1700 nm, more precisely from 400 nm to 700 nm for the visible spectrum and from 700 nm to 1700 nm for the near infrared. The transmittance of a layer to radiation corresponds to the ratio between the intensity of the radiation leaving the layer and the intensity of the radiation entering the layer, the rays of the incoming radiation being perpendicular to the layer. In the remainder of the description, a layer or film is said to be transparent to radiation when the transmittance of the radiation through the layer or film is greater than 70% and preferably greater than 90%.

[0030] In the remainder of the description, a film or layer is said to be oxygen-tight when the permeability of the film or layer to oxygen at 40°C is less than 1.10 1cm3 / (m2*day). The oxygen permeability can be measured according to the ASTM D3985 method entitled "Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using a Coulometric Sensor". In the remainder of the description, a film or layer is said to be water-tight when the permeability of the film or layer to water at 40°C is less than 1.10 *g / (m2*day). The water permeability can be measured according to the ASTM F1249 method entitled "Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor".

[0031] We will now describe in more detail a method of manufacturing a optoelectronic device 100, such as a photodetector or an imager, with reference to Figures 1A, 1B, 1C, 1D and 1E.

[0032] The method comprises at least the following steps: a) providing a substrate 110 covered by a stack of active layers comprising an electron injection layer 140, an organic semiconductor layer 150, a hole injection layer 160, b) forming an encapsulation element on the stack of active layers, the encapsulation element successively comprising a first inorganic layer 170, an organic buffer layer 180 and a second inorganic layer 190.

[0033] More particularly, step b) can be carried out according to the following sub-steps: i) deposit a first inorganic layer 170 full plate, ii) forming an organic buffer layer 180 on the first inorganic layer 170, the part of the first inorganic layer 170 facing the stack of active layers being covered by the organic buffer layer 180 and the other part of the first inorganic layer 170 not being covered by the organic buffer layer 180, iii) etching the first inorganic layer 170, the organic buffer layer 180 acting as a mask during the etching, so as to remove the part of the first inorganic layer 170 not protected by the organic buffer layer 180 (i.e. the part which is not arranged on the stack of active layers), iv) locally forming a second inorganic layer 190 to cover the organic buffer layer 180.

[0034] The encapsulation element thus formed is a stack comprising at least three layers: an organic layer 180 disposed between two inorganic layers 170, 190. Preferably, it is a three-layer. Alternatively, the stack could comprise an alternation of organic layers and inorganic layers, the stack starting and ending with an inorganic layer.

[0035] The first inorganic layer 170 protects the stack of active layers from the solvents used to form / structure the other layers of the encapsulation element.

[0036] Protecting the underlying active layer stack thus makes it possible to improve the electro-optical performance of the photodetector without adding an additional level of photolithography mask.

[0037] The presence of the first inorganic layer 170 also allows to homogenize the underlying surface and obtain a more homogeneous deposition of the organic buffer layer 180.

[0038] The method does not involve any prior treatment on the stack of active layers (such as plasma treatment, etc.), which makes it possible to preserve the properties of the layers.

[0039] Such a method is particularly advantageous because the organic buffer layer 180 acts as a mask during the wet etching of the first inorganic layer 170.

[0040] Finally, the first inorganic layer 170 and the second inorganic layer 190 can thus be made of the same material and deposited with the same deposition technique, which simplifies the process, reduces costs and improves the barrier effect of the multi-layer encapsulation system.

[0041] We will now describe the different stages of the process in more detail.

[0042] The substrate 110 provided in step a) comprises at least a first electrode 120 corresponding to the active zone and a second electrode 130 corresponding to a contact recovery zone 130 of the HIL layer 160. The contact recovery zone is also called bias or BIP (for 'build in Pad').

[0043] In the figures, only one first electrode 120 and one second electrode are shown, but the device may comprise several first electrodes 120 and several second electrodes 130. Preferably, the first electrodes 120 are in matrix form. The device obtained at the end of the method will thus comprise a matrix of photon sensors, called photodetectors, or a matrix of imagers.

[0044] The stack of active layers covers a single first electrode 120 in the figures, but it could cover several first electrodes 120, so as, for example, to form several pixels.

[0045] The electrodes 120, 130 are connected to contact pads 121, 131 ('contact pads') offset from the stack of active layers. The contact pads 121, 131 make it possible to connect the optoelectronic device 100 to an external element, for example to a printed reading circuit, in particular a ROIC ('readout integrated circuit'). The contact pads 121, 131 are connected to the electrodes 120, 130 via interconnections 125, 135 passing through the substrate 110.

[0046] At the end of the process, the contact pads 121, 131 are not covered by the stack of active layers. They are also not covered by the encapsulation element.

[0047] The electrodes 120, 130 and the contact pads 121, 131 are made of a conductive material, preferably chosen from the group comprising: - a conductive oxide such as tungsten oxide (WO3), nickel oxide (NiO), vanadium oxide (V2O5), or molybdenum oxide (MoO3), in particular a transparent conductive oxide (TCO), in particular tin-doped indium oxide (ITO), an aluminum zinc oxide (AZO), Zinc Oxide), a gallium and zinc oxide (GZO, English acronym for Gallium Zinc Oxide), an ITO / Ag / ITO alloy, an ITO / Mo / ITO alloy, an AZO / Ag / AZO alloy or a ZnO / Ag / ZnO alloy; - titanium nitride (TiN); - a metal or metal alloy, for example silver (Ag), gold (Au), lead (Pb), palladium (Pd), copper (Cu), nickel (Ni), tungsten (W), molybdenum (Mo), aluminum (Al), or chromium (Cr) or an alloy of magnesium and silver (MgAg); - a conductive polymer, in particular the PEDOT:PSS polymer, which is a mixture of poly(3,4)-ethylenedioxythiophene and sodium polystyrene sulfonate, or a polyaniline; - carbon, silver and / or copper nanowires; - graphene; and - a mixture of at least two of these materials.

[0048] Preferably, the electrodes 120, 130 and the contact pads 121, 131 are made of a metal or a metal alloy.

[0049] The electrodes 120, 130 and the contact pads 121, 131 are positioned in or on the substrate 110. In other words, while being accessible for making the contacts, they can be projecting, protrude from a main face of the substrate or not protrude from a main face of the substrate, be flush with the surface of the substrate 110.

[0050] The substrate 110 is, for example, made of a dielectric material, for example glass or plastic, or of a semiconductor material, for example silicon.

[0051] By way of example, the substrate 110 integrates an electronic circuit for controlling and reading the photodetector matrix.

[0052] By way of example, the substrate 110 comprises a matrix of reading circuits comprising, for example, thin-film transistors (TFTs).

[0053] As a variant, the substrate 110 integrates a matrix of reading circuits produced in CMOS technology (from the English “Complementary Metal Oxide Semiconductor”). The MOS transistors form the control electronics of the photodiodes.

[0054] The integrated circuit is produced using conventional microelectronics techniques. The conductive pads (electrodes 120, 130) are formed on the surface of the integrated circuit. Among these conductive pads, there are pads formed in a zone of the integrated circuit and which will be used as lower electrodes for the organic photodiodes, and, outside the zone, for example at the periphery of the circuit, pads (contact pads 121, 131) which will be used for polarizing the upper electrode of the photodiodes.

[0055] Conventionally, the integrated circuit may comprise a semiconductor substrate, for example made of monocrystalline silicon, in which and on which insulated gate field effect transistors, also called MOS transistors, for example N-channel and P-channel MOS transistors, are formed, and a stack of insulating layers covering the substrate and the transistors, conductive tracks and conductive vias being formed in the stack for electrically connecting the transistors and the pads. The integrated circuit may have a thickness of between 100 pm and 775 pm, preferably between 200 pm and 400 pm

[0056] During step a), the active zone of the substrate 110 (and in particular the first electrode 120) is covered by a stack comprising successively and preferably constituted by: the electron injector layer 140 (EIL for 'electron injection layer'), the active organic semiconductor layer (OSC for 'organic semiconductor') 150 and the hole injector layer (HIL for 'hole injection layer') 160.

[0057] The second electrode 130 is covered by the HIL layer 160. It is not covered by the other active layers.

[0058] The EIL 140 layer may be deposited, for example, by spin-coating.

[0059] The EIL layer 140 may comprise a self-assembled monomolecular layer or a layer made of a polymer. The self-assembled monomolecular layer may be a layer of hexadecanethiol. The polymer layer may be PEDOT:Tosylate (i.e. a mixture of poly(3,4)-ethylenedioxythiophene and tosylate). It can also be a polyelectrolyte, for example poly[9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene-alt-2,7-(9,9-dioctyfluorene)] (PFN), poly[3-(6-trimethylammoniumhexyl)thiophene] (P3TMAHT) or poly[9,9-bis(2-ethylhexyl)fluorene]-b-poly[3-(6-trimethylammoniumhexyl] thiophene (PF2 / 6-b-P3TMAHT) or poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)].

[0060] The EIL 140 layer may be a metal oxide layer, such as a ZnO layer or an aluminum-doped zinc oxide (AZO) layer.

[0061] The EIL layer 140 is preferably made of propoxylated and / or butoxylated polyethyleneimine (PEI), ethoxylated polyethyleneimine (PEIE).

[0062] The EIL layer 140 may be a mixture of two or more of the aforementioned materials.

[0063] The thickness of the EIL layer 140 is preferably between 0.1 nm and 1 μm, even more preferably between 1 nm and 5 nm. This layer can be grafted onto the pads, be etched by photolithography process (as in the figures) or be a continuous layer having a very low lateral conductivity (not shown in [Fig.2]).

[0064] The active layer 150 is deposited on the EIL layer 140 from a solution of photosensitive semiconductor material.

[0065] The active layer 150 comprises at least one organic material and may comprise a stack or a mixture of several organic materials. The active layer may comprise a mixture of an electron-donating polymer and an electron-accepting molecule. The thickness of the active layer may be between 50 nm and 2 μm, for example of the order of 300 nm.

[0066] The active layer 150 may comprise small molecules, oligomers or polymers. These may be organic or inorganic materials. The active layer may comprise an ambipolar semiconductor material, or a mixture of an N-type semiconductor material and a P-type semiconductor material, for example in the form of superimposed layers or an intimate mixture at the nanometric scale so as to form a bulk heterojunction.

[0067] Examples of P-type semiconductor polymers suitable for producing the active layer are poly(3-hexylthiophene) (P3HT), poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2',l',3'-benzothiadiazo le)] (PCDTBT), poly[(4,8-bis-(2-ethylhexyloxy)-benzo[l,2-b;4,5-b'] di-thiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b] thiophene))-2,6-diyl] (PBDTTT-C), poly[2-methoxy-5-(2-ethyl-hexyloxy)-l,4-phenyl-ilene-vinylene] (MEH-PPV) or poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,lb;3,4-b']dithiophene)-alt-4,7(2,1,3-benzo-ithiadiazole)] (PCPDTBT).

[0068] Examples of N-type semiconductor materials suitable for producing the active layer 47 are fullerenes, in particular C60, [6,6]-phenyl-C61-methyl butanoate (

[60] PCBM), [6,6]-phenyl-C71-methyl butanoate (

[70] PCBM), perylene diimide, zinc oxide (ZnO) or nanocrystals allowing the formation of quantum dots.

[0069] The hole injection layer (HIL) 160 completely covers the active layer 150. It forms a continuous layer from the active layer 150 to the second electrode 130 of the contact recovery zone 130.

[0070] The hole injector layer 160 may be deposited in one or more steps. Different photolithography steps may be used to form this layer.

[0071] The hole injecting layer 160 may be made of an organic material or an inorganic material.

[0072] The hole injecting layer 160 is a material that can be chosen from the group comprising: - a doped conductive or semiconductive polymer, in particular the materials marketed under the names Plexcore OC RG-1100, Plexcore OC RG-1200 by the company Sigma-Aldrich, the polymer PEDOT:PSS, or a polyaniline; - a molecular host / dopant system, in particular the products marketed by the company Novaled under the names NHT-5 / NDP-2 or NHT-18 / NDP-9; - tungsten oxide (WO3); - a metal oxide, for example a molybdenum oxide, a vanadium oxide, ITO, or a nickel oxide; - a polyelectrolyte, for example a fluoro(co)polymer, preferably 1,1,2,2-tetrafluoroethene known under the trade name Nafion; and - a mixture of two or more of these materials.

[0073] During step b), the encapsulation element is formed to cover and protect the active layers.

[0074] The encapsulation element is produced by successively forming the different layers of the stack: the first inorganic layer 170, the organic layer 180 and the second inorganic layer 190.

[0075] During step i), the first inorganic layer 170 is deposited full plate on the substrate 110. The first inorganic layer 170 covers not only the stack of active layers 140, 150, 160 but also the contact pads 121, 131.

[0076] During step ii), an organic buffer layer 180 is formed locally on the first inorganic layer 170. It is formed so as to cover a first part of the first inorganic layer 170 at the level of the stack of active layers and to leave a second part of the first inorganic layer 180 free outside the stack of active layers.

[0077] Step ii) can be carried out according to the following sub-steps: - deposition of the organic buffer layer 180, - structuring the organic buffer layer 180 by photolithography, so that the organic buffer layer 180 only covers the first inorganic layer 170 opposite the stack of active layers.

[0078] During step iii), the first inorganic layer 170 is wet etched.

[0079] During wet etching, the organic buffer layer 180 acts as a mask. In other words, the portion of the first inorganic layer 170 positioned under the mask is not etched. The portion of the first inorganic layer 170 not protected by the mask is etched.

[0080] The etching makes it possible to expose the contact pads 121, 131.

[0081] During step iv), a second inorganic layer 190 is formed to cover the organic layer 180.

[0082] Step iv) can be carried out according to the following sub-steps: - deposition and structuring by photolithography of a resin (called lift-off resin), - full plate deposition of the second inorganic layer 190, - removal of the resin ('lift off') in order to release the contact pads 121, 131 from the substrate 110.

[0083] The resulting encapsulation element comprises, and preferably consists of, a trilayer formed of the first inorganic layer 170, the organic buffer layer 180 and the second inorganic layer 190.

[0084] The first inorganic layer 170 and the second inorganic layer 190 may be made of the same inorganic material or different inorganic materials. They may have the same thickness or different thicknesses. Preferably, the first inorganic layer 170 has a thickness less than the thickness of the second inorganic layer 190.

[0085] The inorganic material is substantially impermeable to water and atmospheric oxygen so as to protect the organic active layers of the stack. Preferably, it is an oxide, for example aluminum oxide (A12O3), titanium dioxide, magnesium oxide, silicon oxide (SiO2) or zirconium oxide, or a nitride, such as silicon nitride (Si3N4).

[0086] The first inorganic layer 170 is preferably a very thin inorganic layer (typically 3 to 25 nm thick). The first inorganic layer 170 is preferably made of alumina. Alumina has good barrier properties for the encapsulation of organic active layers of optoelectronic devices.

[0087] The first inorganic layer 170 and the second inorganic layer 190 are preferably formed by atomic layer deposition (ALD), physical vapor deposition (PVD) or plasma-enhanced chemical vapor deposition (PECVD).

[0088] Preferably, the first inorganic layer 170 and the second inorganic layer 190 are aluminum oxide (A12O3) layers. Such layers are preferably deposited by ALD.

[0089] The thickness of the first inorganic layer 170 is preferably between 3 and 25 nm.

[0090] The thickness of the second inorganic layer 190 is, for example, between 20 and 50 nm.

[0091] The organic buffer layer 180 is, for example, made of a material chosen from epoxy type resins, (meth)acrylate type resins, parylene, poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN) or copolymers based on cyclic olefins (COP).

[0092] The organic buffer layer 180 has, for example, a thickness of between 1 and 10 pm, preferably between 1.5 and 3 pm, for example 2 pm.

[0093] The encapsulation element has a thickness of the order of that of the organic buffer layer 180.

[0094] The different layers of the encapsulation stack and / or the injection layer of holes 160 are preferably transparent.

[0095] The optoelectronic device 100 obtained may be an imager based on an organic photodetector on CMOS or TFT type reading electronics or even a unitary photodetector which may be on CMOS or TFT type reading electronics.

[0096] [Fig.2] represents current-voltage curves obtained without thermal aging (t = Oh) and after thermal aging (at t = 1h, 5h and 10h) for different optoelectronic devices: a device having a three-layer encapsulation element (the first inorganic layer 170, the organic buffer layer 180 and the second inorganic layer 190) and a device having a two-layer encapsulation element (an organic buffer layer and an inorganic layer).

[0097] A very strong rectification of the injection current is observed with thermal aging up to 100 at 150°C when the first inorganic protective layer is integrated into the encapsulation element. For comparison, when this layer is not present, the injection current degrades.

[0098] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art.

[0099] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above.

Claims

Claims

1. A method of manufacturing an optoelectronic device (100), such as a photodetector or an imager, comprising a substrate (110) covered by a stack of active layers comprising an electron injection layer (140), an organic semiconductor layer (150), a hole injection layer (160), the method comprising forming an encapsulation element on the stack of active layers according to the following steps: - depositing a first full-plate inorganic layer (170), - forming an organic buffer layer (180) on the first inorganic layer (170), a first portion of the first inorganic layer (170) facing the stack of active layers being covered by the organic buffer layer (180) and a second portion of the first inorganic layer (170) not being covered by the organic buffer layer (180),- etching the second part of the first inorganic layer (170) not covered by the organic buffer layer (180), by wet etching, - forming a second inorganic layer (190) on the organic buffer layer (180).,

2. The method of claim 1, wherein the first inorganic layer (170) and / or the second inorganic layer (190) are made of a material selected from oxides such as alumina, titanium dioxide, zirconium oxide, silicon oxide, magnesium oxide and nitrides, for example silicon nitride.

3. Method according to one of claims 1 and 2, wherein the first inorganic layer (170) and / or the second inorganic layer (190) are deposited by atomic layer deposition.

4. A method according to any preceding claim, wherein the first inorganic layer (170) and / or the second inorganic layer (190) are made of alumina.

5. A method according to any preceding claim, wherein the first inorganic layer (170) has a thickness of between 3 and 25 nm.

6. A method according to any preceding claim, wherein the substrate (110) comprises a first electrode (120) and a second electrode (130) covered by and in contact with at least one of the layers of the active layer stack and the pads of contact (121, 131) offset and connected, respectively, to the first electrode (120) and to the second electrode (130), the first inorganic layer (170) covering the contact pads (121, 131) during its full-plate deposition, the etching step leading to the release of the contact pads (121, 131).

7. Optoelectronic device (100), such as a photodetector or an imager, comprising a substrate (110) covered by a stack of active layers comprising an electron injection layer (140), an organic semiconductor layer (150), a hole injection layer (160), the stack being protected by an encapsulation element comprising a first inorganic layer (170), an organic buffer layer (180) and a second inorganic layer (190).

8. Device according to claim 7, in which the first inorganic layer (170) is made of a material chosen from oxides such as alumina, titanium oxide, zirconium oxide, and nitrides, for example silicon nitride.

9. Device according to one of claims 7 and 8, in which the first inorganic layer (170) has a thickness of between 3 and 25 nm.

10. Device according to one of claims 7 to 9, in which the first inorganic layer (170) is made of alumina.

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