EP2543073A2

EP2543073A2 - Transparent conductive substrate for optoelectronic devices

Info

Publication number: EP2543073A2
Application number: EP11706269A
Authority: EP
Inventors: Dominique Coster; Jean-Michel Depauw; Laurent Dusoulier
Original assignee: AGC Glass Europe SA
Current assignee: AGC Glass Europe SA
Priority date: 2010-03-04
Filing date: 2011-03-03
Publication date: 2013-01-09
Also published as: WO2011107557A2; WO2011107549A2; EP2543074A2; WO2011107554A3; WO2011107557A3; WO2011107554A2; WO2011107549A3

Abstract

The invention relates to a transparent conductive substrate for optoelectronic devices, comprising a base and a conductive coating comprising doped zinc oxide, said coating being formed by a stack of two layers having different electrical conductivity, namely a so-called low electrical conductivity layer and a so-called high electrical conductivity layer, whereby the so-called low electrical conductivity layer forms the part of the stack closest to the base. According to the invention, the so-called high electrical conductivity layer is a layer comprising zinc oxide doped with m wt.-% of oxide of a doping element where m is less than or equal to 6 and the so-called low electrical conductivity layer is a layer comprising zinc oxide doped with (m/p) wt.-% of oxide of a doping element where p is greater than or equal to 2.

Description

Transparent conductive substrate for devices

optoelectronic

The present invention is in the technical field of transparent conductive substrates for optoelectronic devices.

The present invention relates to a transparent substrate, in particular glass, provided with a conductive coating for optoelectronic devices, to the method of manufacturing this transparent conductive substrate as well as to the optoelectronic devices in which this transparent conductive substrate is incorporated.

The transparent conductive substrate referred to in the present invention can be used as an electrode for extracting or injecting charges into optoelectronic devices such as organic electroluminescent devices known by the acronym OLED (Organic Light Emitting Device). or the light collecting devices such as photovoltaic cells, also called solar cells. The invention is more particularly concerned with thin-film Si-based photovoltaic cells.

There are different types of photovoltaic cells among which there are cells based on Si films. In the current state of the art, optoelectronic devices in thin layers, typically having a thickness of less than 10 μm, consist of of a transparent, flexible or rigid conductive substrate and deposited on the latter, an optoelectronically active layer formed of an inorganic semiconductor material or, more rarely, organic, and contacted on both sides by two electrodes of which at least one transpait nte. The semi-conductor is generally composed of the stack of a p-type layer, an active layer and an n-type layer, together forming a pin or nip junction. The material used is mainly amorphous or microcrystalline silicon. In the first case, the useful range of absorption of photons in the absorbent is between 400 nm and 550 nm. For tandem cells, this useful absorption domain is expanded and covers 400 nm to 1100 nm.

The transparent conductive substrate comprises a support provided with a conductive coating, this conductive coating being more often called by the specialists TCO (of the English Transparent Çonductive Oxide), said support being preferably a glass support. At present, two main industrial techniques are used for the realization of TCO. The first technique is a gas phase pyrolysis method (often referred to by the abbreviation CVD, Chemical Vapor Deposition). Organometallic precursors react in the gas phase at high temperature (> 600 ° C) and a deposit is formed on the surface of the glass. The most commonly deposited material is tin oxide fluoride or antimony doped tin oxide. This technique makes it possible to obtain layers having adequate electrical and optical properties. Advantageously, this technique is applied directly after the formation of the glass (in the production unit called float). This method is then called "on-line".

Another method, "off-line", consists in depositing a material on the surface of the support by vacuum process, said support being preferably n ce in glass. Sputtering (possibly assisted by a magnetic field) is a process well known in the manufacture of layers for glazing used in the residential sector (individual houses) or in the architectural field (buildings and large construction). Depending on the choice of deposited materials, the deposits on the glass make it possible to obtain thermal insulation properties (low emissivity) as well as certain desired hues. In general, this type of deposit is made cold. In the context of TCO sputtering, it is necessary to heat during the growth phase of the layer in order to obtain the correct crystallographic phase. Controlled atmosphere annealing is also possible. Previously, the material most used with the sputtering process was indium tin oxide (ITO). However, the rarefaction of indium greatly increases the cost of this material and alternatives are now considered. ZnO zinc oxide is a promising compound. Indeed, of a conductor behavior in the pure state, the resistivity decreases rapidly with the addition of a dopant such as Ai, Ga, B.

Moreover, in order to limit the manufacturing costs of the optoelectronic device, the active layer must be relatively thin (between 100 nm and a few microns). However, such a layer leads to a low amount of absorbed light and therefore reduced efficiency. To compensate for this effect, it is therefore necessary to increase as much as possible the optical path of the light within the active layer. This is generally achieved by the use of a textured TCO substrate or layer for diffusing or diffracting light in the active layer.

In CVD, texturing or veiling is produced directly during this process. In cathodic sputtering (possibly assisted by a magnetic field), the obtained TCO is not sufficiently textured. Thus the document DE 197 13 215 describes a solar cell whose substrate is covered with a TCO layer, advantageously zinc oxide (ZnO), formed by cathodic sputtering in an argon atmosphere from an aluminum doped ZnO target. In order to give roughness to this TCO layer, normally without asperities, it is attacked either by a chemical process using an acid solution, or by an electrochemical process (anodic etching or reactive ion etching). The attack can be done during or after the deposition of the layer.

The object of the invention is to provide a transparent conductive substrate for optoelectronic devices which is an alternative to existing substrates. More particularly, it is a question of providing a transparent conductive substrate for photovoltaic cells as well as its manufacturing method.

A second object that the present invention sets is to provide a photovoltaic cell incorporating the transparent conductive substrate.

To this end, the invention relates to a transparent conductive substrate for an optoelectronic device comprising a support and a conductive coating based on doped zinc oxide, said coating consisting of a single stack of two layers of different electrical conductivity, a so-called of low electrical conductivity and a so-called layer of high electrical conductivity, the so-called low conductivity layer being the layer constituting the stack closest to the support, such that the so-called layer of high electrical conductivity is a layer based on zinc doped with m% by weight of oxide of a first doping element with m less than or equal to 6.0, preferably with m less than or equal to 4.0, more preferably with m equal to 2.0 and in that the so-called low electrical conductivity layer is a layer based on zinc oxide doped with (m / p)% by weight of oxide of a second doping element with p greater than or gal to 2, preferably p is greater than or equal to 3, more preferably with p greater than or equal to 4. However, in order to obtain a sufficient conductivity of said low conductivity layer, p is preferably less than or equal to 15, more preferably p is less than or equal to 12. to combine the advantage of two different doping rates in order to optimize the electrical and optical properties as well as the surface microstructure related to light scattering.

By transparent conductive substrate is meant a substrate whose light absorption is at most 30%, preferably at most 20% in the wavelength range of visible light. A range of wavelengths from wavelengths of near-infrared radiation to those of far-ultraviolet radiation may also define the range of transparency of the electrodes according to the invention. In particular, in the case of an organic photovoltaic cell, the range of transparency is defined by a range of wavelengths ranging from the near infrared to that of the visible light.

The support on which is deposited the conductive coating of the transparent conductive substrate according to the invention is preferably rigid. The function of the support is to support and / or protect the electrode. The support preferably has a geometric thickness of at least 3.85 mm. The geometric thickness means the average physical thickness. According to a particular embodiment, the support comprises at least one total or partial surface structuring on at least one of the faces of the substrate. Generally, the method of structuring the support comprises at least one of the processes selected from etching, rolling and / or laser etching. The chemical attack of the support comprises at least matting and / or etching (for example by etching with hydrofluoric acid of a glass ό silicosodocalcique). The rolling method comprises at least the step of structuring the support by the impression impression of a pattern using at least one printing roll. The support may be made of glass, rigid plastics material (for example: organic glass, polycarbonate) or flexible polymeric films (for example: polyvinyl butyral (PVB), polyethylene terephthalate (PET), vinyl acetate copolymer and ethylene (EVA)). The support is preferably a glass sheet. The glasses are mineral or organic. The mineral glasses are preferred. Among these, the clear or colored silicosodocalcic glasses are preferred in the mass or on the surface. More preferably, they are extra clear silicosodocalcic glasses. The term extra clear designates a glass containing at most 0.020% by weight of the total Fe glass expressed in Fe ₂ O ₃ and preferably at most 0.015% by weight, the latter because of its low content of Fe oxide has a low light absorption. The use of the latter therefore makes it possible to obtain a higher transmission in the optoelectronic device incorporating it, more preferentially in the photovoltaic cell.

The conductive coating based on doped zinc oxide deposited on the support consists of a stack of two layers of different electrical conductivity. A so-called low electrical conductivity layer based on doped zinc oxide and a so-called high electrical conductivity layer based on doped zinc oxide, the so-called low conductivity layer being the layer constituting the stack closest to the support. . The high electrical conductivity layer is a layer based on zinc oxide doped with m% by weight of oxide of the doping element with m less than or equal to 6.0, preferentially less than or equal to 4.0, plus preferably equal to 2.0. Preferably, the high electrical conductivity layer is a layer based on zinc oxide doped with m% by weight of oxide of the doping element with m equal to 6.0, preferably with m equal to 4.0. more preferentially with m equal to 2.0. The so-called low electrical conductivity layer is a layer based on zinc oxide doped with (m / p)% by weight of oxide of the doping element with p greater than or equal to 2, preferably with p greater than or equal to 3, more preferably with p greater than or equal to 4. Preferably, the so-called low electrical conductivity layer is a layer based on zinc oxide doped with (m / p)% by weight of oxide of the doping element with p equal to 2, preferably with p equal to 3, more preferably with p equal to 4. The doping elements used for the so-called layer of high electrical conductivity and the so-called layer of low electrical conductivity may be of different chemical nature, preferably they are of the same nature. The geometric thickness of the conductive coating based on doped zinc oxide is between 400 nm and 1200 nm. Advantageously, the conductive coating has a surface texturing such that it corresponds to a RMS roughness value in the range of values from 55 nm to 200 nm, preferably equal to 55 nm. Such texturing is obtained after acid etching of the coating.

According to a particular embodiment of the preceding mode, the transparent conductive substrate according to the invention is such that the doping element is selected from Al and / or Ga and / or B. Preferably, the doping element is Al and / or Ga. More preferably, the dopant is Al.

According to a particular embodiment, the transparent conductive substrate according to the invention is such that the so-called layer of high electrical conductivity is a layer based on zinc oxide doped with m% by weight of aluminum oxide with m included between 1.7 and 3.0 and in that the so-called low electrical conductivity layer is a layer based on zinc oxide doped with (m / p)% by weight of aluminum oxide with m / p included between 0.2 and 1.2. According to a particular embodiment, the transparent conductive substrate is such that the doping element can be of different nature from one layer to another. In this case, it is possible to obtain stacks such as AZO / GZO or GZO / AZO.

According to a particular embodiment, the transparent conductive substrate according to the invention is such that the geometric thickness of each layer constituting the conductive coating is between 100 nm and 600 nm, preferably between 250 nm and 500 nm, more preferably between 300 nm and 450 nm.

According to a particular embodiment, the transparent conductive substrate according to the invention is such that the conductive coating comprises a buffer layer based on zinc oxide doped with Al at q% by weight of aluminum oxide with q between 0.5 and 4.0, preferably with q equal to 2.0, said buffer layer being the layer constituting the conductive coating furthest away from the support, the geometrical thickness of the buffer layer being between 100 nm at 500 nm, preferably between 100 nm and 400 nm. The buffer layer advantageously makes it possible to circumscribe the acid attack making it possible to obtain texturing of the surface of the conductive coating to this single buffer layer, said buffer layer having, after said attack, a roughness value R.M.S. in the range of values from 55 nm to 200 nm after texturing, preferably of the order of 55 nm.

According to a particular embodiment ¹ , ³ the transparent conductive substrate according to the invention is such that the conductive coating comprises a barrier layer, said barrier layer being the layer of the conductive coating closest to the support.

The barrier layer makes it possible in particular to protect the optoelectronic device against any pollution by migration of alkali from the support, for example silicosodocalcic glass, and thus an extension of the life of the device. The barrier layer comprises at least one compound selected from: · titanium oxide, zirconium oxide, aluminum oxide, yttrium oxide and the mixture of at least two of them ;

Mixed zinc-tin, zinc-aluminum, zinc-titanium, zinc-indium, tin-indium oxide;

Silicon nitride, silicon oxynitride, silicon oxycarbide, silicon oxycarbonitride, aluminum nitride, aluminum oxynitride and the mixture of at least two of them;

This barrier layer being optionally doped or alloyed with tin.

The barrier layer has a thickness between 50 nm and 300 nm.

According to a particular embodiment, the transparent conductive substrate according to the invention is such that it comprises, consists or consists essentially of, successively from the support:

A so-called low electrical conductivity layer, said layer being a layer based on zinc oxide doped with (m / p)% by weight of oxide of a second doping element with p greater than or equal to 2, preferably with p greater than or equal to 3, more preferably with p greater than or equal to 4,

A so-called high conductivity layer, said high layer being a layer based on zinc oxide doped with m% by weight of oxide of a first doping element with m less than or equal to 6.0, preferably with m lower or equal to 4.0, more preferably with m equal to 2.0,

A buffer layer based on zinc oxide doped with Al at q% weight of aluminum oxide with q between 0.5 and 4.0, preferably with q equal to 2.0, said buffer layer being the layer constituting the conductive coating furthest away from the support, the geometrical thickness the buffer layer being between 100 to 500 nm, preferably between 100 to 400 nm.

According to a particular embodiment, the transparent conductive substrate according to the invention is such that it comprises, consists or consists essentially of, successively from the support: · a barrier layer

A buffer layer based on zinc oxide doped with Al at q% by weight of aluminum oxide with q of between 0.5 and 4.0, preferably with q equal to 2.0, said layer buffer being the layer constituting the conductive coating furthest from the support, the geometric thickness of the buffer layer being between 100 to 500 nm, preferably between 100 to 400 nm.

Embodiments of the conductive substrate transparent are not limited to the modes described above but may also result from a combination of two or more of them.

The second subject of the invention concerns the process for manufacturing the transparent conductive substrate according to the invention. This substrate comprises a support and a conductive coating. The process for producing the transparent conductive substrate according to the invention is a method in which all the layers based on doped zinc oxide constituting the conductive coating are deposited on the support by a cathodic sputtering technique assisted by a field magnetic. When present, the barrier layer can be deposited by any type of vacuum process, such methods are sputtering techniques, possibly assisted by a magnetic field, plasma deposition techniques, deposition techniques. CVD (Chemical Vapor Deposition) and / or PVD (Physical Vapor Deposition) type. Once the conductive coating is deposited, it is etched by a chemical process using an acid solution at room temperature (of the order of 25 ° C) in order to give the conductive coating a roughness R.M.S. of the order of 55nm. The roughness R.M.S. (Root Mean Square) is a measure of measuring the mean square deviation of roughness. This roughness R.M.S. quantifies on average the height of the peaks and troughs of roughness, compared to the average height. The apparatus usually used to obtain these measurements is the Atomic Force Microscope (AFM). Examples of acidic solutions are dilute hydrochloric acid solutions (eg 0.5% by volume HCl).

According to a preferred mode of implementation, the method of manufacturing the transparent conductive substrate according to the invention is such that it comprises the following steps: Sputter deposition of a so-called low electrical conductivity layer on the support, said layer being based on zinc oxide doped with (m / p)% by weight of the oxide of the doping element with higher p or equal to 2, preferably p greater than or equal to 3, more preferably with p greater than or equal to 4,

Sputter deposition of a so-called layer of high electrical conductivity, said layer being based on zinc oxide doped with m% by weight of oxide of the doping element with m less than or equal to 6.0, preferably m less than or equal to 4.0, more preferably with m equal to 2.0,

• acid etching to give the conductive coating a roughness value R.M.S. in the range of values from 55 nm to 200 nm, preferably of the order of 55 nm, for example using a hydrochloric acid solution diluted to 0.5% by volume for 10s, 20s or 30 s at room temperature.

According to a preferred embodiment, the method for manufacturing the transparent conductive substrate according to the invention is such that it comprises the following steps: · sputter deposition of a so-called low electrical conductivity layer on the support, said layer being based on zinc oxide doped with (m / p)% by weight of the oxide of the doping element with p greater than or equal to 2, preferably p greater than or equal to 3, more preferably with p higher or equal to 4,

Depositing a buffer layer based on zinc oxide doped with Al at q% by weight of aluminum oxide with q of between 0.5 and 4.0, preferably with q equal to 2.0 said buffer layer being the layer constituting the conductive coating furthest away from the support, the geometrical thickness of the buffer layer being between 100 nm to 500 nm, preferably between 100 nm to 400 nm.

• acid etching to give the conductive coating a roughness value R.M.S. in the range of values from 55 nm to 200 nm, preferably of the order of 55 nm, for example using a hydrochloric acid solution diluted to 0.5% by volume for 10 seconds, s or 30 s at room temperature.

According to a preferred mode of implementation, the method of manufacturing the transparent conductive substrate according to the invention is such that it comprises the following steps:

Deposit on the support of a barrier layer by a vacuum deposition technique, said layer comprising at least one compound selected from titanium oxide, zirconium oxide, aluminum oxide, aluminum oxide, yttrium and the mixture of at least two of them, zinc-tin mixed oxide, zinc-aluminum mixed oxide, zinc-titanium mixed oxide, zinc-zinc mixed oxide, indium, tin-indium mixed oxide, silicon nitride, silicon oxynitride, silicon oxycarbide, silicon oxycarbonitride, aluminum nitride, aluminum oxynitride and mixture of at least two of them

Sputter deposition of a so-called low electrical conductivity layer, said layer being based on zinc oxide doped with (m / p)% by weight of the oxide of the doping element with p greater than or equal to 2, preferably p greater than or equal to 3, more preferably with p greater than or equal to 4,

Sputter deposition of a so-called low electrical conductivity layer, said layer being based on zinc oxide doped with (m / p)% by weight of the oxide of the doping element with p greater than or equal to 2, preferably p higher or equal to 3, more preferably with p greater than or equal to 4,

The third object of the invention relates to an optoelectronic device comprising a transparent conductive substrate according to the invention. More particularly, the invention relates to an optoelectronic device as it is a photovoltaic cell.

The transparent conductive substrate according to the invention will now be illustrated with the aid of the following figures. The figures show in a nonlimiting manner a number of structures of transparent conductive substrates, more particularly layer stack structures constituting the conductive coating included in the substrate according to the invention. These figures are purely illustrative and do not constitute a scale presentation structures.

Fig. 1: Cross section of a transparent conductive substrate according to the invention, the substrate comprising a conductive coating consisting of a first layer of low electrical conductivity and a second layer of high electrical conductivity.

Fig. 2: Cross section of a transparent conductive substrate according to the invention, the substrate comprising a conductive coating consisting of a stack consisting of a barrier layer, a first layer of low electrical conductivity and a second conductivity layer high electric.

Fig. 3: Cross-section of a transparent conductive substrate according to the invention, the substrate comprising a conductive coating consisting of a stack consisting of a barrier layer, a first layer of low electrical conductivity, a second conductivity layer High electric and buffer layer

Fig. 4: Schematic representation of the pilot line with which the transparent conductive substrate according to the invention has been manufactured.

FIG. 1 represents an example of a stack constituting a transparent conductive substrate according to the invention. The transparent conductive substrate (1) has the following structure from the support (10):

A stack comprising a first layer of low electrical conductivity (12) and a second layer of high electrical conductivity (13)

FIG. 2 represents an example of a stack constituting a transparent conductive substrate according to the invention. The transparent conductive substrate (1) has the following structure from the support (10): • A barrier layer (11)

FIG. 3 represents an example of a stack constituting a transparent conductive substrate according to the invention. The transparent conductive substrate (1) has the following structure from the support (10):

• A barrier layer (11)

• A buffer layer (14)

FIG. 4 shows a schematic representation of the pilot line with which the transparent conductive substrate according to the invention has been manufactured. That consists of an airlock (4), a heating zone comprising a heating system (2) and a deposition zone (30) comprising two doped ZnO targets (3 and 3 '). The distance (5) represents the distance separating the heating system and the target, this is of the order of 600 mm. The heating system has two infrared lamps.

The various steps of the deposition process are summarized in Table 1. Table 1 shows two columns, the first column shows the various steps of the method of manufacturing a transparent conductive substrate according to the invention, the second column shows the speeds of moving the glass for each step of the method of manufacturing a transparent conductive substrate according to the invention. The deposit is made from target zinc oxide ceramic (ZnO) doped with aluminum oxide (Al ₂ O ₃ ) according to different doping (% by weight). The sputtering power applied to the cathode is 2 kW. The sputtering gases are Ar and O ₂ . O ₂ is introduced in very low percentage or not at all (0-0.7%). The total deposition pressure is of the order of 0.53 Pascal. Programming has been carried out in order to minimize the distances between the heating zone and the deposition zone. The conductive coating is manufactured using several successive deposits. The heating system (2) of the heating zone (20) is used to heat the glass at a temperature between 250 ° C and 400 ° C, preferably at a temperature of 350 ° C.

Table 1:

The transparent conductive substrate according to the invention will be illustrated by a number of examples. ZnO zinc oxide doped with aluminum is commonly abbreviated as AZO. The percentage by weight (%) of aluminum oxide (Al ₂ O ₃ ) is also presented. Table 2 shows the optical and electrical properties of a substrate according to the invention, Example 1, and of two non-conforming comparative examples. to the invention, Examples 1R and 2R.

Example 1 is a transparent conductive substrate consisting of a clear 3.85 mm silicosodocalcic glass covered by a layer of AZO 0.5% by weight of Al ₂ O ₃ and a 2.0% AZO layer. Al ₂ O ₃ weight. The first layer (AZO 0.5% by weight Al ₂ O ₃ ) is approximately 490 nm thick while the second layer (AZO 2.0% by weight Al ₂ O ₃ ) is one about 420 nm thick. Example 1R is a transparent conductive substrate not according to the invention consisting of a silicosodocalcic glass covered by a layer made solely of AZO 0.5% by weight of Al ₂ O ₃ having a thickness of the order of 700 nm. Example 2R is a transparent conductive substrate not according to the invention consisting of a silicosodocalcic glass covered by a layer made solely of AZO 2.0% by weight of Al ₂ O ₃ having a thickness of the order of 700nm. The comparison of optical and electrical properties shows that:

^■ With stacking alternating the two dopings of AZO (Example 1), we can observe before pickling: o a sheet resistance (7.7 ohm / Q) being between Comparative Examples 1R (AZO 0.5% by weight of Al ₂ O ₃ (33.2 ohm / D)) and 2R (AZO 2.0% by weight of Al ₂ O ₃ (5.6 ohm / D)).

a mobility (25.7 cm ² / Vs) (Example 1) comparable to the mobilities measured on Comparative Examples 1R and 2R (26.5 cmW.s). o for transmission, ΓΑΖΟ 2% by weight of Al ₂ O ₃ (example

2R) has a lower value (76.1%) than ΓΑΖΟ 0.5% by weight of Al ₂ O ₃ (example 1R) (80.1%). Example 1 has a slightly higher (80.5%) transmission at ΓΑΖΟ 0.5% by weight of Al ₂ O ₃ . o The veil is very weak (0.6 to 0.9%) for the three examples

^■ After treatment in dilute HCl at different times, we see that the resistance per square increases while TIM transmission increases. It is therefore possible to adjust the chemical attack (concentration, duration) in order to obtain an electrical and optical optimum.

Table 2:

The optical values as well as the haze were measured by an Ultra-Scan Pro spectrophotometer apparatus from the firm Hunterlab. The transmission values (TIM) take into account the wavelengths useful for power generation of the photovoltaic cell (between 400 and 1050 nm for tandem cells). The measurement is carried out in a submerged cell: a liquid of refractive index intermediate between the TCO and the glass is placed during the measurement. This method of measurement is used when the veil is too important for a correct measurement (scattering of the incident light). This measurement method makes it possible to avoid any loss of light on the veil. The veil is defined according to the standard ASTMD10003 which defines the haze as the percentage of light passing through the substrate is deflected from the incident light beam at an angle greater than 2.5 degrees on average. The haze can be measured by methods known in the art. The electrical properties were measured by the Hall probe method (4 points).

Table 3 shows the optical and electrical properties of a substrate according to the invention, Example 1, and two comparative examples not in accordance with the invention, Examples 3R and 4R. Table 3 compares the optical and electrical properties of Example 1 according to the invention with commercial samples (VU (Example 3R) and AN14 (Example 4R) from AGC Solar). Unlike other deposits, the UV is deposited on an extraclear glass. These commercial samples are made by the pyrolytic technique (CVD) and not undergone acid attack.

Table 3:

It is observed that Example 1 after 15 s of acid attack has an intermediate square resistance to Examples 2R and 3R. The type of microstructures obtained after acid etching of a layer of AZO 2 w% by weight of Al ₂ O ₃ may have a better light distribution for a photovoltaic application. By suitable microstructure is meant the microstructures recommended in Kluth's articles. et al. Thin Solid Films, 442, (2003), 80, 5836; from Berginski et al. J. Appl. Phys., 101, 074903 (2007) and Rech B. et al. , Thin Solid Films, 511-512 (2006), 548.

Claims

A transparent conductive substrate for an optoelectronic device comprising a support and a conductive coating based on doped zinc oxide, said coating consisting of a single stack of at least two layers of different electrical conductivity, a so-called electrical conductivity layer. high and a so-called low electrical conductivity layer, the so-called low conductivity layer being the layer constituting the stack closest to the support, characterized in that the so-called layer of high electrical conductivity is a layer based on zinc oxide doped with m% by weight of oxide of a first doping element with m less than or equal to 6.0 and in that the so-called low electrical conductivity layer is a layer based on zinc oxide doped with p)% by weight of oxide of a second doping element with p greater than or equal to 2,

2. transparent conductive substrate according to claim 1, characterized in that the conductive coating based on doped zinc oxide has a roughness value R.M.S. within the range of 55 nm to 200 nm,

Transparent conductive substrate according to any one of the preceding claims, characterized in that the doping element is selected from Al and / or Ga and / or B,

4. transparent conductive substrate according to any one of the preceding claims, characterized in that the geometric thickness of each layer constituting the conductive coating is between 100 nm and 600 nm, 5. transparent conductive substrate according to any one of the preceding claims, characterized in that the conductive coating comprises a buffer layer based on zinc oxide doped with Al at q% by weight of aluminum oxide with q between 0,

5 and 4.0, said buffer layer being the layer constituting the conductive coating furthest away from the support.

6. transparent conductive substrate according to claim 5, characterized in that the buffer layer based on zinc oxide doped with Al has a roughness value of R.M.S. in the range of values from 55 nm to 200 nm,

7. Transparent conductive substrate according to any one of the preceding claims, characterized in that the conductive coating comprises a barrier layer, said barrier layer being the layer of conductive coating closest to the support.

8. transparent conductive substrate according to any one of claims 5 to 6, characterized in that it comprises successively from the support:

A so-called low electrical conductivity layer, said layer being a layer based on zinc oxide doped with (m / p)% by weight of oxide of a second doping element with p greater than or equal to 2,

A so-called high conductivity layer, said high layer being a layer based on zinc oxide doped with m% by weight of oxide of a first doping element with m less than or equal to 6.0, a buffer layer based on zinc oxide doped with Al at q% by weight of aluminum oxide with q of between 0.5 and 4.0, said buffer layer being the layer constituting the conductive coating furthest from at the support, the thickness geometric layer of the buffer layer being between 100 to 500 nm.

9. transparent conductive substrate according to claim 7, characterized in that it comprises successively from the support:

• a barrier layer

A so-called high conductivity layer, said high layer being a layer based on zinc oxide doped with m% by weight of oxide of a first doping element with m less than or equal to 6.0, a buffer layer based on zinc oxide doped with Al at q% by weight of aluminum oxide with q of between 0.5 and 4.0, said buffer layer being the layer constituting the conductive coating furthest from to the support, the geometric thickness of the buffer layer being between 100 to 500 nm.

10. A method of manufacturing a transparent conductive substrate according to claim 2, characterized in that it comprises the following successive steps:

• Deposition by sputtering of a so-called low electrical conductivity layer on the support, said layer being based on zinc oxide doped with (m / p)% by weight of the oxide of the doping element with higher p or equal to 2,

• Sputtering deposition of a so-called conductivity layer a high electrical current, said layer being based on zinc oxide doped with m% by weight of oxide of the doping element with m less than or equal to 6.0,

• Acid attack to give the conductive coating a roughness value R.M.S. in the range of values from 55 nm to 200 nm.

11. A method of manufacturing a transparent conductive substrate according to claim 6, characterized in that it comprises the following steps:

Sputter deposition of a so-called low electrical conductivity layer on the support, said layer being based on zinc oxide doped with (m / p)% by weight of the oxide of the doping element with higher p or equal to 2,

Sputter deposition of a so-called layer of high electrical conductivity, said layer being based on zinc oxide doped with m% by weight of oxide of the doping element with m less than or equal to 6.0,

Depositing a buffer layer based on zinc oxide doped with Al at q% by weight of aluminum oxide with q of between 0.5 and 4.0, said buffer layer being the layer constituting the conductive coating furthest from the support, the geometrical thickness of the buffer layer being between 100 to 500 nm,

• acid etching to give the conductive coating a roughness value R.M.S. in the range of values from 55 nm to 200 nm,

12. A method of manufacturing the transparent conductive substrate according to claim 7, characterized in that it comprises the following successive steps: Deposit on the support of a barrier layer by a vacuum deposition technique, said layer comprising at least one compound selected from titanium oxide, zirconium oxide, aluminum oxide, aluminum oxide, yttrium and the mixture of at least two of them, zinc-tin mixed oxide, zinc-aluminum mixed oxide, zinc-titanium mixed oxide, zinc-zinc mixed oxide, indium, tin-indium mixed oxide, silicon nitride, silicon oxynitride, silicon oxycarbide, silicon oxycarbonitride, aluminum nitride, aluminum oxynitride and mixture of at least two of them,

Sputter deposition of a so-called low electrical conductivity layer, said layer being based on zinc oxide doped with (m / p)% by weight of the oxide of the doping element with p greater than or equal to 2, · sputter deposition of a so-called layer of high electrical conductivity, said layer being based on zinc oxide doped with m% by weight of oxide of the doping element with m less than or equal to 6.0 ,

• acid etching to give the conductive coating a roughness value R.M.S. in the range of values from 55 nm to 200 nm.

13. A method of manufacturing the transparent conductive substrate according to claim 7, characterized in that it comprises the following successive steps: · deposition on the support of a barrier layer by a vacuum deposition technique, said layer comprising at least one compound selected from titanium oxide, zirconium oxide, aluminum oxide, yttrium oxide and the mixture of at least two of them, zinc-tin mixed oxide , the mixed zinc oxide aluminum, zinc-titanium mixed oxide, zinc-indium mixed oxide, tin-indium mixed oxide, silicon nitride, silicon oxynitride, silicon oxycarbide, oxycarbonitride silicon, aluminum nitride, aluminum oxynitride and the mixture of at least two of them,

An optoelectronic device comprising a transparent conductive substrate according to any one of claims 1 to 9.

Optoelectronic device according to claim 14, characterized in that it is a photovoltaic cell.