WO2014090394A1

WO2014090394A1 - Organic electronic device with a translucent top electrode and method for depositing such an electrode

Info

Publication number: WO2014090394A1
Application number: PCT/EP2013/003721
Authority: WO
Inventors: Fouzia Hannour; Ganesan Palaniswamy; Rene Albert Johan Janssen; Dhritiman GUPTA; Martinus Maria Wienk
Original assignee: Stichting Materials Innovation Institute (M2I)
Priority date: 2012-12-10
Filing date: 2013-12-10
Publication date: 2014-06-19

Abstract

The invention relates to an organic electronic device, comprising a layered stack with an opaque substrate, a current collector layer on top of the substrate, a electron transport layer, a hole transport layer, and a photoactive layer between the electron transport layer and the hole transport layer, wherein a current collector structure is provided on top of the layered stack, and wherein the opaque substrate is a metallic substrate. In addition, the invention relates to a method for manufacturing an organic electronic device, the method comprising applying a current collector structure having an adjacent layer comprising a high conductivity polymer material with a conductivity of 10⁴ - 10⁵ S/m, wherein the adjacent layer is applied by providing the high conductivity polymer material on a stamp material; pressing the stamp material on a receiving surface with the high conductivity polymer material facing the receiving surface such that the high conductivity polymer material and the receiving surface are in contact, and peeling off the stamp material such that the high conductivity polymer material is transferred to the receiving surface.

Description

ORGANIC ELECTRONIC DEVICE WITH A TRANSLUCENT TOP ELECTRODE AND METHOD FOR DEPOSITING SUCH AN ELECTRODE

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic electronic device, such as a solar cell or an OLED, with a translucent top electrode, comprising a high conductivity polymer material. Furthermore, the invention relates to a method for depositing such an electrode.

2. Description of the Related Art

Organic electronics is a vast emerging field, which comprises organic light emitting diodes, organic photovoltaics, dye sensitized solar cells. Organic solar cells (OSCs) have the potential to deliver cost-competitiveness on par with conventional energy means such as fossil fuels and with inorganic solar cells with high efficiency and lifetime, but high cost of raw materials and processing. This cost- competitiveness of OSC rests in its virtue of low cost of raw materials and their processing. The same applies to (White) OLEDs, which are potential future lighting source with higher energy efficiencies compared existing lighting sources

In above devices, Indium tin oxide (ITO) has been extensively used in organic optoelectronic devices as transparent electrode. However, practical issues like limited indium feedstock and device issues like incompatibility of ITO with flexible substrates due to its mechanical brittleness have triggered the search for replacements. As an alternative several other transparent conductive materials such as graphene, single wall carbon nanotubes, silver nanowires, and metal oxides have been investigated.

Semitransparent OSCs with a glass/ITO substrate have been demonstrated by Y- Y. Lee et al. (ACS Nano, 201 1, p. 6564-6570) using a transparent top electrode consisting of ten monolayers of graphene, laminated on the photoactive layer (PAL). In these devices, illumination from the graphene side resulted in lower power conversion efficiencies (PCEs) owing to higher recombination loss near the graphene electrode. In addition, there is concern about the hydrophobicity of graphene. Hence, its use as bottom electrode and as intermediate contact layer in tandem devices has limited applicability.

As electrode nearer the substrate, silver nanowires have been shown to perform on par with ITO. Laminated silver nanowires as an electrode further from the substrate perform similar to the ITO based devices, although in such devices, electrical shorts play a limiting role.

Traditionally, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) formulations, such as Clevios P VP A14083, have been used as the transparent hole transport layer on top of ITO to improve its work function and smoothen the surface. The low intrinsic conductivity in this material however gives rise to a high sheet resistance and makes it unsuitable for a stand-alone replacement for ITO. Therefore, PEDOT:PSS has been combined with a semitransparent metal as top electrode for OSCs, with negative bottom and positive top contacts on opaque substrates. However, the use of PEDOT:PSS as transparent top electrode is severely hampered by poor wetting of such water based dispersions on hydrophobic PAL surfaces. Further, certain PEDOT:PSS formulations are highly acidic and are known to corrode the materials of previously applied layers, e.g. the materials of the PAL.

A flexible organic solar cell using a zinc oxide (ZnO) layer as a hole blocking layer and PEDOT:PSS as an electron blocking layer is described in the American patent publication US2011/0237019. A flexible plastic substrate is coated with a conductive film comprising ITO, a hole blocking layer, comprising ZnO, an active layer comprising poly(3-hexylthiophene) (P3HT) and [6,6]phenyl-C6i -butyric acid methyl ester (PCBM), a hole selective layer comprising PEDOT:PSS and a metal electrode, such as gold or silver.

A disadvantage of the described flexible organic solar cell of US2011/0237019 is that the flexible substrate is a translucent substrate and therefore the light receiving side of the solar cell, as the metal electrode is usually an opaque layer of metal. As the substrate will be turned such as to be able to receive daylight, modifications will have to be made before this organic solar cell will behave as with common translucent substrates.

It would therefore be desirable to provide an alternative container construction that alleviated the perceived inconveniences of the prior art. BRIEF SUMMARY OF THE INVENTION

According to the invention there is provided an organic electronic device, comprising a layered stack comprising an opaque substrate, a current collector layer on top of the substrate, a electron transport layer, a hole transport layer, an active layer capable of generating a charge carrier effect, wherein the active layer is between the electron transport layer and the hole transport layer and a current collector structure is provided on top of the layered stack, wherein the opaque substrate is a metallic substrate. Optionally, the metallic substrate may be provided with an insulating layer on a surface of the metallic substrate adjacent to the current collector layer.

The organic electronic device can be an organic solar cell wherein the active layer is a photoactive layer that generates a charge carrier effect by generating free charge carriers upon radiation of light on to the photoactive layer. Alternatively, the organic electronic device can be an organic light emitting diode wherein the active layer is an emissive electroluminescent layer in which layer charge carriers from an external circuit generate a charge carrier effect by recombination of the charge carriers to send out photons for generating light. Furthermore, the organic electronic device can be a solid state dye sensitized solar cell wherein the active layer is a photoelectrochemically active layer that generates a charge carrier effect by generating free charge carriers upon radiation of light on to the photoelectrochemically active layer.

A stacked organic electronic device is built upon an opaque substrate on which a current collector layer to collect the charge carriers for transport to or from an external circuit is applied. On a side facing away from the opaque substrate, the current collector is provided with either an electron transport layer or a hole transport layer to collect and transport the respective free charge carriers that, in the case of a solar cell, have been generated by the photoelectrochemically active or photoactive layer or that will recombine in the emissive electroluminescent layer of an OLED to send out photons and generate light. The active layer is situated in between the electron transport layer and the hole transport layer. The photoactive layer of the solar cells cannot be completely translucent, because in that circumstance it cannot absorb or convert light. The most effective photoactive layer will absorb most of the light. The layers provided on a side of the active layer facing away from the opaque substrate are translucent, such that light can pass these layers and reach the photoelectrochemically active or photoactive layer to generate free charge carriers in case of the solar cells, or be radiated from the emissive electroluminescent layer through these layers.

The use of an opaque substrate has the advantage that the stacked organic electronic device has been constructed such that the light can enter or leave the device only on the side remote from the substrate. By using a metal substrate, the organic electronic device can be integrated with packaging or building materials. In addition, metal substrates can be thin foils (for example 0.025 mm to 0.3 mm) or thick metal plates (at least 0.3 mm to for example 1.5 mm). The thin foils can take non-flat forms and the thick plates makes flat as well as profiled surfaces. The organic electronic device can be provided on any surface, such as a flat or curved surface. Furthermore, metallic substrates, in particular steel based substrates, have mechanical robustness, thermal and chemical stability and excellent barrier properties against oxygen and water. The barrier properties protect the organic layer and are beneficial for overall lifetime of the organic electronic device. Therefore, the use of metallic substrates partly reduce the cost of barrier protection needed compared to for example with plastic substrate-based organic devices. Metallic substrates are furthermore compatible with roll-to-roll processing, such as printing of the organic electronic device on the top and offers mechanical stability as well as temperature resistance, if needed for processing organic electronic devices.

When using a metal substrate, for monolithic modules in which multiple organic electronic devices are interconnected by electrically contacting top and bottom electrodes of adjacent organic electronic devices, an insulating layer should be provided between the current collector layer and the substrate. This insulating layer can be a polymeric, ceramic or insulating metal oxide layer. Preferably, the insulating layer comprises a polymer material with a relatively high resistivity compared to the substrate, such as a polyimide. When modules are made via a shingling route, in which the entire module has one common bottom and one common top electrode, the organic electronic device can be built without the insulating layer, where the metal itself is used as current collecting layer.

Preferably, the current collector layer comprises a metallic layer acting as an optical back reflector, for example, but not limited to, comprising one of chromium, gold, silver and aluminum or a combination thereof. This combination can either be an alloy of two of the mentioned metals or a coating comprising at least two of these metals. A back reflector enhances the light absorption inside the organic layer by reflecting light back and forth and hence increases the overall efficiency. Furthermore it enhances options for providing the metal and organic electronic devices with a color, which can be aesthetically appealing for application for building integrated products and consumer products.

In an embodiment, the electron transport layer comprises a semiconducting metal oxide, such as zinc oxide (ZnO) or titanium dioxide (Ti0₂) for the organic solar cell. Both ZnO and Ti0₂ have hole blocking and electron accepting properties making it advantageous to integrate them with the current collector layer. The electron transport layer should be translucent and have high electron mobility and a relatively wide bandgap. The work function of the electron transport layer should match with the effective conduction band (also called lowest unoccupied molecular orbital or LUMO) of the photoactive layer. Zinc oxide and titanium oxide fulfil these requirements, however, any material fulfilling these requirements may be used. Zinc oxide and titanium oxide have energy levels for their conduction bands at about -4.2 eV versus vacuum. This energy level corresponds to the LUMO level of commonly used fullerene acceptor molecules in organic solar cells such as PCBM. Hence the negative charges (known as electrons) in the fullerene acceptors can easily be transferred to zinc oxide or titanium oxide, without significant energy barrier. The valence bands of zinc oxide and titanium oxide are well below -7.0 eV, such that they effectively block the transport of positive charges (known as holes) from the donor molecules in the photoactive layer. The optical band gaps of zinc oxide and titanium oxide are at about 3.2 eV such that they are almost translucent and only absorb some UV light. Hence these layers are selective electron collectors, or hole blockers, and do not significantly interfere with the absorption of light by the photoactive layer.

For organic light emitting diodes (OLEDs) the electron transport layer may comprise one of 2-(4-biphenyl)-5-(4-t-butylphenyl)-l,3,4-oxadiazole (PBD), tris(8- hydroxyquinoline) aluminum (Alq3) or oxadiazole derivatives with naphthyl substituent (BND) or combinations. For solid state dye sensitized solar cells, the electron transport layer can comprise one of 2,2'-7,7'- tetrakis(N,N-di-p-methoxyphenylamine) 9,9'-spirobifiuorene

(spiro-OMeTAD), bipyridine cobalt complex or cesium tin iodide (CsSnI_3-x) or a combination thereof.

Upon irradiation of the solar cell by white light radiation with a wavelength of about 300 nm to about 1500 nm, i.e. from near UV to near infrared, for generating a photovoltaic effect, the energy of the waves will penetrate the translucent layers of the stack until they reach the photoactive layer and generate charge carriers in the photoactive layer. The charge carriers are electrons and holes, with respectively a negative and a positive charge. The interfaces between the photoactive layer and the charge transport layers, i.e. the hole transport layer and the electron transport layer, act as diodes, such that electrons are guided toward the electron transport layer and the holes are guided towards the hole transport layer. In such a way recombination of the free charge carriers is prevented and transport of the oppositely charged electrons and holes at opposite electrodes is ensured.

According to an embodiment, the current collector layer is subsequently and in sequence coated with the electron transport layer, the active layer, the hole transport layer and the current collector structure, wherein the hole transport layer is translucent and is adjacent to the current collector structure. The current collector structure is designed to provide optical access to the layer stack below.

In this conventional configuration of the stacked electronic device, the electron current is transported by the electron transport layer to the current collector layer. The hole current is transported by the hole transport layer to the current collector structure. In order to have optical access to the active layer, the hole transport layer in the conventional configuration may be at least partly translucent.

Alternatively, the current collector layer can be subsequently and in sequence coated with the translucent hole transport layer, the active layer, the translucent electron transport layer, a further current collector layer and the outer current collector structure, wherein the electron transport layer and the further current collector layer are translucent and the further current collector layer is adjacent to the current collector structure. The current collector structure is designed such to provide optical access to the layer stack below and preferably minimizes blocking of light. In this alternative and inverted configuration, the holes are transported by the hole transport layer to the current collector layer. The electrons are transported by the electron transport layer and the further current collector layer to the current collector structure. In such a way, this inverted configuration is a solar cell with an inverted polarity as compared to the above described solar cell. In order to have optical access to the active layer, i.e. let light reach the active layer or let light leave the active layer, the electron transport layer and the further current transport layer in the inverted configuration can be at least partly translucent.

The hole transport layer in the inverted configuration comprises a material with a relatively low conductivity of less than 1 S/m, for example in the range of, but not limited to 0.01-0.3 S/m, such as low conductivity PEDOT:PSS. Other materials that may be used as hole transport layer are thin semiconducting metal oxides such as NiO, Mo0₃, V₂0₅, Ti0₂ or ZnO, or doped organic or polymeric materials such as Ν,Ν'- bis(l-naphthyl)-N,N'-diphenyl-l,l '-biphenyl-4,4'-diamine (alpha-NPD) and a poly(N- vinylcarbazole) (PVK), a polyaniline (PANI), or NPB = l ,4-bis(l - naphthylphenylamino)biphenyl. Either of these materials may be doped to increase the conductivity to desired levels. Because the hole transport layer in the inverted configuration is in direct contact with the current collector layer, the conductivity can be, but not necessarily is, modest as charged holes only need to be transported over the thickness of the layer. Preferably the hole transport layer in the inverted configuration is conductive, has an energy level that corresponds to the energy level of the holes in the donor of the active layer, and does not absorb light. In the inverted configuration the hole transport layer is directly deposited on the metal. The metal has a high conductivity and ensures low resistance transport in a direction in the plane of the device. Because of the metal the conductivity of the hole transport layer is not very critical in the inverted structure because charges only need to be transported over less than about 100 nm.

Preferably, the further current collector layer of the inverted configuration , or the hole transport layer of the conventional configuration, adjacent to the current collector structure has a relatively high conductivity of about, but not limited to, 10⁴ - 10⁵ S/m, preferably about 6-9x 10⁴ and comprises a high conductivity polymer material, such as high conductivity doped poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). However, even higher conductivity levels would be very beneficial as long as the material remains translucent.

Organic electronic devices on an opaque substrate such as steel require a transparent top electrode with high lateral conductivity to collect and conduct free charge carriers with minimal resistive loss. Indium tin oxide (ITO) is extensively used in organic optoelectronic devices as a transparent electrode. However, practical issues like limited indium feedstock and device issues like incompatibility of ITO with flexible substrates due to its mechanical brittleness have triggered the search for replacements. Moreover, due to vacuum process that are involved in deposition of the ITO layer pose a bottle neck in increasing the production speed of the devices. The high conductivity polymer material comprised in the layer adjacent to the current collector structure acts as a replacement of an expensive indium tin oxide (ITO) layer. To minimize resistive losses in large area devices, the conductivity polymer material can be combined with metal grids.

In the inverted configuration as described above, it is furthermore preferred that between the further current collector layer and the electron transport layer a contact layer is provided for levelling the electron transport layer and contacting the further current collector layer adjacent the current collector structure. In the inverted configuration, the electron transport layer can have a rather rough surface, for example due to the use of metal oxide nanoparticles in the layer, such that conformal contact between the layer of high conductivity polymer material and the semiconducting metal oxide is difficult to achieve. Conformal contact is the effect of a locally defined, intimate contact without voids between the elastomeric stamp and the substrate. Therefore, the contact layer is applied on top of the electron transport layer, for example by spin coating, to planarize the electron transport layer surface and facilitate the conformal contact with the high conductivity polymer material. The contact layer also provides high surface energy required for a successful lamination of the further current collector layer, preferably comprising high conductivity polymer material. In addition, the contact layer provides corrosion protection to the previously applied layers when the further current collector layer is deposited from an acidic solution. Preferably, the contact layer comprises a polymer material deposited from a solution with an acidity level measured in pH of at least 3.0 or higher for preventing the metal oxide layer to dissolve, preferably a pH between 6.0-8.0, more preferably a pH between 6.5 and 7.5, most preferably about 7.0. The pH modification of the solution used to deposit the polymer material is needed to prevent the underlying metal oxide layer from dissolving during deposition. This is important when using ZnO, but can be less restrictive for other metal oxides, such as for Ti0₂. Due to dissolution by an acidic solution deposited on top during subsequent fabrication steps, the absorbance of the metal oxide tends to decrease below pH 3.0. Additionally, a dramatic loss in wetting quality and film formation properties of the polymer material can be observed at low pH values. When applied in multilayer solar cells using semiconducting metal oxide as an electron transport layer, the polymer material should therefore have a pH of at least 3.0, preferably between 5.0 and 8.0.

In a further embodiment, the high conductivity polymer material can be processed from a solution using at least one processing additive or dopant, such as, but not limited to, dimethyl sulfoxide (DMSO), ethylene glycol, sorbitol, fluorosurfactant, such as Zonyl FS 300, or an ionic liquid, such as 1 ,3-alkylimidazoliumborate salts, including l-ethyl-3-methylimidazolium tetracyanoborate (EMIM TCB) and/or 1 -butyl - 3-methylimidazolium tetrafluoroborate (BMIM BF₄). The role of the dopant is to increase the conductivity of the polymer material layer such that the material can be used as an electrode or current conducting layer. The dopant has no active role after deposition. It functions as a co-solvent that changes the morphology of the layer and thereby the conductivity.Preferably, the photoactive layer of the organic solar cell comprises a donor-acceptor blend, such as poly(3-hexylthiophene) (P3HT) and [6,6]phenyl-C61 -butyric acid methyl ester (PCBM), preferably in a weight ratio between 5:1 and 1 :5, such as 2:1 or 1 :2 and more preferably in a weight ratio of about 1 :1. The preferred ratio depends on the donor-acceptor combination and can include any ratio available. The actual choice for the two materials can be very diverse, as many donor-acceptor combinations have been described in the prior art. These can be semiconducting polymers, oligomers, or small molecules or any combination thereof. Also inorganic semiconductors can be used. The donor and acceptor molecules used in one layer should possess offset energy levels such that upon excitation of either the donor or the acceptor by light an electron transfers from the donor to the acceptor, leaving a positive charge (known as hole) in the donor material and creating a negative charge (known as electron) in the acceptor material. For OLEDs, the emissive electroluminescent layer can comprise an iridium complex fluorescent material in PVK or triphenylamine derivates. The photoelectrochemically active layer of the solid state dye sensitized solar cells (DSSC) can comprise a titanium oxide dyed with dye molecules, for instance Ruthenium polypyridyl complexes with TBA+ (tetrabutylammonium) at two carboxyl groups (N719 dye) or a cyclopentadithiophene- bridged donor-acceptor dye (Y123).

In addition, the metallic substrate is preferably selected from carbon steel, stainless steel, aluminum, copper, nickel, chromium, tin, or titanium or a combination thereof. The metallic substrate may optionally be coated with metallic, organic, inorganic or hybrid coatings. Usually, the current collector structure comprises a bus bar structure comprising a metal such as, but not limited to, silver, aluminum, tin, nickel and copper.

The invention furthermore relates to a method for manufacturing an organic electronic device comprising a layered stack, the method comprising:

- applying a current collector layer on a metallic substrate;

- providing a electron transport layer, a hole transport layer, an active layer between the electron transport layer and the hole transport layer, and a current collector structure having an adjacent layer comprising high conductivity polymer material with a conductivity of 10⁴ - 10⁵ S/m, wherein the adjacent layer is applied by

- providing the high conductivity polymer material on a stamp material,

- pressing the stamp material on a receiving surface with the high conductivity polymer material facing the receiving surface such that the high conductivity polymer material and the receiving surface are in contact, and

- peeling off the stamp material such that the high conductivity polymer material is transferred to the receiving surface.

The base on which the organic electronic device is constructed is a metallic substrate. Optionally, the method may comprise providing the metallic substrate with an insulating layer on a surface of the metallic substrate adjacent to the current collector layer. The insulating layer prevents the highly conductive metallic substrate from interfering with the current circuit of the solar cell. A current collector for collecting charge carriers after being generated in the solar cell is applied onto the substrate. On the current collector a electron transport layer and a hole transport layer are provided to transport the charge carriers generated or recombined in the active layer between the electron and hole transport layers. A current collector structure is applied on top of the stacked electronic device structure. The layers on top of the active layer can be translucent in order to let the light reach or leave the active layer. The layer adjacent the collector structure comprises a high conductivity polymer material with a conductivity of about, but not limited to, 10⁴ - 10⁵ S/m, preferably 6-8.5x 10⁴ S/m. The application of this layer is on the layered stack is done by transferring the high conductivity polymer material from a stamp material to a receiving surface of the layered stack. Stamp-transfer lamination of dry high conductivity polymer material film is a useful technique because it benefits from less energy consuming fabrication and/or the use of any intermediate layer to facilitate coating of high conductivity polymer material in a roll-to-roll fashion. Unlike other lamination techniques which involve "gluing" of two layers, here the high conductivity polymer material is directly spin coated or printed on an elastomeric stamp material, such as poly(dimethylsiloxane) (PDMS), and after laminating it onto the receiving surface, the stamp material is delaminated leaving the bare high conductivity polymer material surface available for deposition of the current collector structure. On a roll-to-roll scale this process can be envisaged as the conductive polymer layer applied and cured on to PDMS foil to form a film. Later this film will be laminated, at below-mentioned conditions, on to the layer stack and the PDMS foil can be re-used.

The use of an elastomeric polymer as a carrier stamp material overcomes the wetting issues that are normally observed when providing transparent top electrodes on stacked electronic device structures. Advantageously, defect free or substantially defect free polymeric transparent electrodes may be provided.

According to an embodiment, the method comprises after pressing the stamp material on the receiving surface; annealing the stack at a temperature between 50°C to 100°C, preferably between 80°C to 90°C, for a time between 1-5 min, preferably between 1 -3 min. Annealing helps to restore the hydrophobicity of the PDMS surface, presumably by molecular reorientation on the surface, and therefore provides the driving force for delamination.

According to a further embodiment, the method comprises applying subsequently on the current collector layer in sequence:

- the electron transport layer comprising a semiconducting metal oxide,

- the photoactive layer,

- the hole transport layer, and

- the current collector structure,

wherein the hole transport layer is translucent and comprises the high conductivity polymer material and the receiving surface is a surface of the active layer facing away from the electron transport layer. Such a configuration of the layered stack is called a conventional configuration where the high conductivity polymer material is applied directly on the active layer and the current collector structure is applied on the high conductivity polymer material layer.

Alternatively, the method comprises applying subsequently on the current collector layer in sequence:

- the hole transport layer,

- the active layer,

- the electron transport layer comprising the semiconducting metal oxide,

- a further current collector layer, and

- the current collector structure,

wherein the electron transport layer and the further current collector layer are translucent and the further current collector layer comprises the high conductivity polymer material. This configuration of the layered stack is called an inverted configuration.

In a further embodiment, the step of applying the translucent electron transport layer comprises:

- applying the semiconducting metal oxide layer on the active layer for electron transport,

- providing a contact layer over the semiconducting metal oxide layer for levelling the semiconducting metal oxide layer and contacting the high conductivity polymer material adjacent the current collector structure. In the inverted configuration, the semiconducting metal oxide layer can have a rather rough surface, such that conformal contact between the layer of high conductivity polymer material and the semiconducting metal oxide is difficult to achieve. In addition, a contact layer is therefore applied, by spin coating for example, on top to planarize the semiconducting metal oxide surface and facilitate the conformal contact with the high conductivity polymer material. The contact layer also provides high surface energy required for a successful lamination of the high conductivity polymer material. In addition to the electron transport layer and the further current collector layer, the contact layer can be translucent such that the light is not blocked from reaching or leaving the active layer. Further, the contact layer prevents, or at least reduces the corrosion of the semiconducting metal oxide layer when the further current collector layer is deposited from an acidic solution.

Preferably, the current collector structure comprises a metal structure deposited, by a suitable technique such as, for example evaporation using shadow masking, printing or lamination, that allow sufficient lateral resolution, e.g. about 40 μηι for shadow masking, in the pattern, preferably via a simple and cheap procedure.

The current collector structure should be transparent, i.e. let pass light into or let light leave the active layer such that the active layer can be illuminated for generating free charge carriers or can illuminate with the photons generated upon recombination of the charge carriers. In addition, the current of the charge carriers collected in the current collector layer will have to be transported into the external circuit of the solar cells or to the active layer in the OLED. Therefore, the current collector structure should not cover the complete free surface of the layered stack of the solar cell. A current collector structure encompassing the current collector layer but letting through light for illuminating the photoelectrochemically or photoactive layer or illumination of the active layer can be obtained by applying an open structure leaving the larger part of the free surface of the layered stack uncovered, preferably in the shape of a grid pattern.

Preferably, the high conductivity polymer material comprises doped poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), preferably processed from a solution containing at least one processing additive or dopant of the group of dimethyl sulfoxide (DMSO), ethylene glycol, sorbitol, fluorosurfactant, such as Zonyl FS 300, and an ionic liquid, such as an imidazolium salt, including an imidazolium salt with an alkyl group at at least one of the nitrogen atoms, such as an alkylimidazolium cation with a borate anion, for instance l -ethyl-3-methylimidazolium tetracyanoborate (EMIM TCB) and/or l-butyl-3-methylimidazolium tetrafluoroborate (BMIM BF₄).

Traditionally, poly(3,4-ethylenedioxythiophene):poly(styrene

sulfonate) (PEDOTrPSS) formulations (Clevios P VP A14083) have been used as the transparent hole transport layer on top of ITO to improve its work function and smoothen the surface. The (intentionally) low intrinsic conductivity (less than 1 S/m and in the range of 0.01-0.3 S/m) in this material however gives rise to a high sheet resistance and makes it unsuitable for a stand-alone replacement to ITO. Owing to the significant improvements in PEDOT:PSS formulations in recent years, significantly more conductive PEDOT.PSS formulations have become available, such as the highly conducting PEDOT:PSS (Clevios PH 1000) exhibiting a conductivity of about 6xl0⁴ - 10⁵ S/m (upon addition of 5 wt% dimethyl sulfoxide, DMSO to the solution used for depositing the layer). In combination with DMSO, other secondary dopants or processing additives including ethylene glycol, fluorosurfactant, such as Zonyl FS 300, or ionic liquids, such as l-ethyl-3-methylimidazolium tetracyanoborate (EMIM TCB) and l-butyl-3-methylimidazolium tetrafluoroborate (BMIM BF₄), have been used to further improve the conductivity by a factor of two to three. BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will be appreciated upon reference to the following drawings of a number of exemplary embodiments, in which:

Figure 1 a shows a perspective view of a first embodiment of a layered solar cell according to the invention of the organic electronic device;

Figure lb shows a perspective view of a further embodiment of the layered solar cell;

Figure 2 shows the different stages of building the first embodiment of the layered solar cell;

Figure 3 shows the different stages of building the further embodiment of the layered solar cell;

Figure 4 shows a drawing of a device contact pad for the layered solar cell. DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Figure 1 a shows a perspective view of a first embodiment of the layered organic solar cell 1 in a conventional configuration. The organic solar cell 1 is arranged on a steel substrate 2 with a polyimide insulating layer 3. On the insulating layer 3 a silver current collector layer 4 is deposited. The current collector layer 4 functions as an optical back reflector and electrode. By way of the uncovered part 5 of the current collector layer 4 the generated electron current in the solar cell can be transported to an external electrical circuit. The solar cell 1 is furthermore built with an electron transport layer 6, made of spin coated ZnO from a solution further described below. A photoactive layer 7 made of a donor-acceptor blend of poly (3-hexylthiophene) (P3HT) and [6,6]phenyl-C61 -butyric acid methyl ester (PCBM), in a 1 :1 weight ratio. On top of the photoactive layer 7 a hole transport layer 8 made of the highly conducting poly(3,4- ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT.PSS, Clevios PH 1000) is deposited by stamp-transfer lamination, which is further described below. On top of the hole transport layer 8 a busbar structure 9, for connection to the external electrical circuit, as counter electrode has been deposited.

Figure lb shows a perspective view of a further embodiment of the layered solar cell 12 in an inverted configuration. The solar cell 12 is built on a steel substrate 2 with a polyimide insulating layer 3. The silver current collector electrode 4 has an external part 5 for connection to an external electronic circuit. A hole transport layer 8 is deposited on the current collector electrode 4 and made of PEDOT:PSS (Clevios P VP A14083 or Clevios PH 1000), the specific type of PEDOT:PSS is not critical for the inverted configuration. On top of the hole transport layer 8 the photoactive layer 7 is made of a P3HT:PCBM donor-acceptor blend. The electron transport layer 6 is made of nanoparticles of ZnO, leaving a relatively rough surface. On top of the ZnO layer 6 a contacting layer 10 of neutral-pH PEDOT:PSS is provided to obtain a good conformal contact with the further current collector layer 11 of Clevios PH 1000. The current collector structure 9 being a busbar structure is deposited on top of the layered stack forming the organic solar cell 12 in the inverted configuration.

Figure 2 shows the different stages of building a first embodiment of the layered solar cell 1 in the conventional configuration. Figure 3 shows the different stages of building the further embodiment of the layered solar cell 12 in the inverted configuration. The steel substrates 2 (0.7 mm thick, RMS surface roughness ~ 3.73 nm) for both configurations were cleaned by sonicating in acetone and soapwater followed by rinsing with normal water and sonicating in 2-propanol for few minutes. The steel substrates 2 were spin coated with a layer of polyimide (PI2525) 3 at 2000 rpm spin- speed and annealed inside a glovebox at 350 °C for 3 hours to yield a robust insulation on steel (thickness > 3.5 μηι). Then, the silver current collector layer 4 (99.99%, Sigma- Aldrich) of about 100 nm thick was evaporated onto the PI2525 coated steel substrate 2 through a shadow mask.

The organic solar cell 1 with the conventional configuration shown in Fig. 2 was fabricated by spin coating an electron transport layer 3 of ZnO onto the substrate 2 followed by spin coating the P3HT:PCBM photoactive layer 7. ZnO sol-gel ink was prepared by adding 1 ml (milliliter) of 2- methoxyethanol and 30 μΙ_, (microliter) of ethanolamine to 109 mg zinc acetate dihydrate and the mixture was stirred at room temperature for 1 h. Zinc acetate dihydrate (purity 98%), 2-methoxyethanol (anhydrous purity 99.8%) and ethanolamine (purity 99%) were used as received. This ink was directly spun on the insulated substrate 2 at 2000 rpm spin speed and was subsequently annealed at 150 °C in air to yield a 64 nm thick film. The ZnO layer 6 was not patterned, since the sheet resistance even after UV photodoping was found quite high (~ 20 ΜΩ/D (ΜΩ/square)). Poly(3-hexylthiophene) (P3HT, purity >98% head to tail, n = 54,000-75,000 g/mol) : [6,6]phenyl-C61 -butyric acid methyl ester (PCBM, purity >99%) (P3HT:PCBM) solutions were prepared in different concentrations (20, 30, and 40 mg/ml) by dissolving P3HT and PCBM in ort/zo-dichlorobenzene (o-DCB, purity 99%) at a ratio of 1 :1 and stirring overnight at 70 °C. The polymer was spin coated at different spin speeds to achieve different thicknesses of about 190 and 290 nm. Next, the substrate 2 was annealed at 110 °C for 30 min. The optimum thickness for the conventional configuration was 190 nm, which was achieved with a concentration of 30 mg/ml and a spin speed of 600 rpm. The optimum thickness for the inverted configuration was 290 nm, which was achieved with a concentration of 40 mg/ml and a spin speed of 600 rpm. A hole transport layer 8 of PHI 000 (highly conductive Clevios PH 1000, sonicated and filtered using 5.0 μηι filters) was laminated on top of P3HT:PCBM layer 7. For Clevios PH 1000 lamination, hardened polydimethylsiloxane (PDMS) stamps 13 were prepared by mixing PDMS and the curing agent (Sylgard 184 Base and Curing Agent) in 10: 1 ratio and curing it at 100 °C for 1 hr against polished Si0₂ surface. PDMS stamps (few mm thick) was cut into the desired size and was treated with mild N₂ plasma (70 W, 0.1 mbar, 15 s) to enable spin coating of Clevios PH 1000 on top of the PDMS. 5 wt % dimethylsulfoxide (DMSO) was added to Clevios PH 1000 and the mixture was put in a laboratory ultrasonic bath for few hours prior to spin coating. The filtered Clevios PH 1000 ink was subsequently spun on plasma treated PDMS at 1000 rpm to yield a 120 nm thick film. After spin coating the Clevios PH 1000 layer was left in air for drying for about 3-5 minutes. Next, the PDMS stamp was placed onto the receiving surface 15 with the Clevios PH 1000 side facing down. A conformal contact with the receiving surface 15 is established spontaneously and also by applying mild pressure. Application of external pressure only ensures good contact between the two surfaces and is not an essential parameter for success of the lamination process. The whole stack 1 was then annealed at moderate temperature (80-90 °C) for 2 min. Afterwards, the PDMS stamp 13 was peeled off mechanically after cooling down the stack 1. Lamination was performed in ambient conditions. Devices were completed by evaporating a pattern of 100 nm thick Ag busbars 9 surrounding the bottom CCL electrode 4 through shadow masking, as shown in Figure 4.

Figure 3 shows the different stages of building a further embodiment of the layered solar cell 12 known as an inverted configuration. The inverted configuration solar cell 12 was fabricated by spin coating a hole transport layer 8 of PEDOT-PSS (low conductive Clevios P VP A14083) onto the insulated steel substrate 2 followed by spin coating the P3HT:PCBM photoactive layer 7. The substrate 2 was subsequently annealed at 1 10 °C for 30 min. A ZnO nanoparticle (particle size ~5 nm) dispersion in 2-propanol (concentration 24 mg ml^-1) was prepared and was spin coated at 1500 rpm spin speed onto the PAL 7 to form an electron transport layer 6. Next, the substrates were annealed at 120 °C for 5-10 min. The ZnO nanoparticle layer provides a rather rough surface profile (RMS roughness ~3.93 nm). An additional contacting layer 10 of pH-neutral PEDOT:PSS is therefore spin coated on top to planarize the receiving surface 16 and facilitate the conformal contact with the PDMS stamp 13 comprising the Clevios PH 1000 further current collector layer 1 1. It also provides high surface energy required for a successful lamination. Diluted neutral-pH PEDOT:PSS Neutral-pH PEDOT:PSS (by adding deionized water and 2-propanol in the following ratio (PEDOT : water : 2-propanol = 500 μΐ. : 500 μΙ_, : 100 μΐ,) (microliter)) was directly spin-coated on the ZnO-nanoparticle layer 6 at 5000 rpm to yield a thickness of 30 nm. Finally, the Clevios PH 1000 layer 11 was laminated as the further current collector layer 1 1 as previously described. The device 12 was completed by evaporating a pattern of Ag busbars 9 through shadow masking, as shown in Figure 4.

LIST OF PARTS

1. Organic solar cell, conventional configuration

2. Opaque substrate

3. Insulating layer

4. Current collector layer (CCL)

5. External connection of CCL

6. Electron transport layer (ETL)

7. Photoactive layer (PAL)

8. Hole transport layer (HTL)

9. Current collector structure

10. Contacting layer

1 1. Further CCL

12. Organic solar cell, inverted configuration 13. Stamp material

14. External connection of current collector structure

15. Receiving surface PAL

16. Receiving surface ETL

Claims

CLAIMS ganic electronic device (1), comprising a layered stack comprising:

an opaque substrate (2),

a current collector layer (4) on top of the substrate,

a electron transport layer (6),

a hole transport layer (8),

an active layer (7) capable of generating a charge carrier effect, wherein the active layer is between the electron transport layer and the hole transport layer and a current collector structure (9) is provided on top of the layered stack, characterized in that the opaque substrate is a metallic substrate.

Organic electronic device according to claim 1 , provided with an insulating layer (3) on a surface of the metallic substrate adjacent to the current collector layer.

Organic electronic device according to claim 2, wherein the insulating layer comprises a polymer material with a relatively high resistivity relative to the metallic substrate, such as a polyimide.

Organic electronic device according to any of the preceding claims, wherein the current collector layer comprises a metallic layer comprising one of gold, silver, chromium, aluminum or a combination thereof, acting as an optical back reflector.

Organic electronic device according to any one of the preceding claims, wherein the electron transport layer comprises a semiconducting metal oxide, such as zinc oxide or titanium dioxide.

Organic electronic device according to any one of the preceding claims, wherein the current collector layer is subsequently and in sequence coated with the electron transport layer, the active layer, the hole transport layer and the current collector structure, wherein the hole transport layer is translucent and is adjacent to the current collector structure.

7. Organic electronic device according to any of the claims 1-5, wherein the current collector layer is subsequently and in sequence coated with the hole transport layer, the active layer, the electron transport layer, a further current collector layer (1 1) and the current collector structure, wherein the electron transport layer and the further current collector layer are translucent and the further current collector layer is adjacent to the current collector structure.

8. Organic electronic device according to claim 6 or 7, wherein the layer adjacent to the current collector structure has a conductivity of about 10⁴ - 10⁵ S/m and comprises a high conductivity polymer material, such as high conductivity doped poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS).

9. Organic electronic device according to claim 7 or 8, wherein the further current collector layer adjacent the current collector structure comprises a contact layer (10) for levelling the electron transport layer and contacting the further current collector layer adjacent the current collector structure.

Organic electronic device according to claim 8 or 9, wherein the high conductivity polymer material comprises at least one processing additive or dopant selected from the group of dimethyl sulfoxide (DMSO), sorbitol, ethylene glycol, a fluorosurfactant, and an ionic liquid such as a 1 ,3- alkylimidazoliumborate.

Organic electronic device according to claim 7-10, wherein the translucent hole transport layer comprises a material with a conductivity of less than 1 S/m, preferably about 0.01-0.3 S/m, such as low conductivity PEDOT:PSS or thin semiconducting metal oxides such as NiO, Mo0₃, V205 or doped organic or polymeric materials such as N,N'-bis(l-naphthyl)-N,N'-diphenyl-l,r-biphenyl- 4,4'-diamine (alpha-NPD) and a poly(N-vinylcarbazole) (PVK) or a polyaniline (PANI).

Organic electronic device according to any of the preceding claims, wherein the active layer comprises a polymer donor-acceptor blend, such as poly(3- hexylthiophene) (P3HT) and [6,6]phenyl-C61 -butyric acid methyl ester (PCBM) in a weight ratio between 5: 1 and 1 :5.

Organic electronic device according to any of the preceding claims, wherein the metallic substrate is selected from carbon steel, stainless steel, aluminum, copper, nickel, chromium, tin, or titanium, or a combination thereof optionally coated with metallic, organic, inorganic or hybrid coatings.

Organic electronic device according to any of the preceding claims, wherein the current collector structure comprises a metallic bus bar structure, such as silver, aluminum, tin, nickel or copper.

Organic electronic device according to any of the preceding claims, wherein the active layer is a photoactive layer and the organic electronic device is an organic solar cell.

16. Organic electronic device according to any of the claims 1-14, wherein the active layer is an emissive electroluminescent layer and the organic electronic device is an organic light emitting diode.

17. Organic electronic device according to any of the claims 1-14, wherein the active layer is a photoelectrochemically active layer and the organic electronic device is a solid state dye sensitized solar cell. 18. Method for manufacturing an organic electronic device (1), the method comprising:

applying a current collector layer (4) on a metallic substrate (2); providing an electron transport layer (6), a hole transport layer (8), an active layer (7) capable of generating a charge carrier effect, wherein the active layer is between the electron transport layer and the hole transport layer, and a current collector structure (9) having an adjacent layer comprising a high conductivity polymer material with a conductivity of 10⁴ - 10⁵ S/m, wherein the adjacent layer is applied by

providing the high conductivity polymer material on a stamp material (13), pressing the stamp material on a receiving surface (15, 16) with the high conductivity polymer material facing the receiving surface such that the high conductivity polymer material and the receiving surface are in contact, and

peeling off the stamp material such that the high conductivity polymer material is transferred to the receiving surface.

Method according to claim 18, comprising providing the metallic substrate with an insulating layer (3) on a surface of the metallic substrate adjacent to the current collector layer.

Method according to claim 18 or 19, comprising after pressing the stamp material on the receiving surface; annealing the stack at a temperature between 50°C to 100°C, preferably between 80°C to 90°C, for a time between 1-5 min, preferably between 1-3 min.

Method according to any one of claim 18-20, comprising applying subsequently on the current collector layer in sequence:

the electron transport layer comprising a metal oxide,

the active layer,

the hole transport layer, and

the current collector structure,

wherein the hole transport layer is translucent and comprises the high conductivity polymer material and the receiving surface is a surface of the active layer facing away from the electron transport layer. Method according to any one of claims 18-21, comprising applying subsequently on the current collector layer in sequence:

the hole transport layer,

the active layer,

the electron transport layer comprising metal oxide,

a further current collector layer (11); and

the current collector structure,

wherein the electron transport layer and the further current collector layer are translucent and the further current collector layer comprises the high conductivity polymer material.

Method according to claim 22, wherein the step of applying the electron transport layer comprises:

applying a metal oxide layer on the active layer for electron transport, providing a contact layer (10) over the metal oxide layer for levelling the metal oxide layer and contacting the high conductivity polymer material adjacent to the current collector structure.

Method according to any one of claims 18-23, wherein applying the current collector structure comprises depositing a metal structure with a shape following the periphery of the current collector layer, preferably using shadow masking.

Method according to any one of claims 18-24, wherein the high conductivity polymer material comprises doped poly(3,4 ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT:PSS), preferably doped by at least one dopant or processing additive of the group of dimethyl sulfoxide (DMSO), ethylene glycol, sorbitol, a fluorosurfactant, and an ionic liquid such as a 1,3- alkylimidazoliumborate.

26. Method according to any of claims 23-25, wherein the contact layer comprises a polymer material and the method comprises depositing the contact layer from a composition with a pH of- at least 3.0 or higher for preventing the metal oxide to dissolve during deposition, preferably a pH between 6.0 to 8.0.