METHOD FOR ELECTRICAL CHARACTERIZATION OF AN ABSORBENT MATERIAL UNDER VARIABLE ILLUMINATION

Abstract

A method for the electrical characterization of a photovoltaic sample (100) comprising a layer of absorber material (112) and N pairs of adjacent electrodes (108.1 – 108.4), comprising: a) defining or calculating a target value for the layer resistance of the absorber layer; b) for each pair of adjacent electrode pairs having different inter-electrode distances di and d i+1, determining a value I i,i+1 of illumination of the absorber layer such that a value for the layer resistance of the absorber layer determined by linear interpolation between measured values ​​and resistances of the electrode pairs is as close as possible to the target value; c) determining a value R Sh of the layer resistance of the absorber layer and a value R c of the contact resistance of one of the measuring electrodes by linear interpolation between at least three of the measured values ​​and / or for the different values ​​I i,i+1.Figure for the abbreviation: figure 1.

Description

Title of the invention: METHOD FOR THE ELECTRICAL CHARACTERIZATION OF AN ABSORBER MATERIAL UNDER VARIABLE ILLUMINATION Technical field

[0001] The invention relates to the field of the electrical characterization of an absorber material, i.e. a photovoltaic conversion material suitable for use in the production of photovoltaic cells. The invention can be used to characterize, for example, photovoltaic structures based on crystalline silicon, with passivated contacts and high performance. The invention can in particular be used to determine the resistive losses obtained in photovoltaic cells in operation, i.e. under illumination, produced with the absorber material thus characterized. State of the prior art

[0002] Several techniques have been developed to map the performance of a photovoltaic cell, i.e. to electrically characterize different regions of the photovoltaic cell.

[0003] Current-voltage measurements (IV measurements), in the dark or under illumination, are commonly used to evaluate the performance of photovoltaic cells or elements of these cells, and to understand the phenomena at the origin of certain limitations in the performance of the cells. Such an IV measurement applied to a photovoltaic cell consists of measuring the electric current delivered by the cell while applying an electric voltage to its terminals. This measurement makes it possible in particular to determine the short-circuit current, the open-circuit voltage, as well as the current and voltage at the maximum power of the photovoltaic cell.

[0004] The "Transfer Length Method" or TLM, also called "transfer length method", makes it possible to determine the conductivity of a layer of material and the contact resistivity between this layer of material and conductive measuring electrodes formed on this layer of material. This method is implemented from a photovoltaic sample comprising at least one layer of absorber material (the same as that used to produce the photovoltaic cell) on which several conductive measuring electrodes are arranged. The measuring electrodes are, for example, of elongated shape, arranged parallel to each other and spaced apart by a variable distance from each other, i.e. such that the distances between two neighboring or adjacent measuring electrodes are different from one pair of measuring electrodes to the other. These distances are called inter-electrode distances.

[0005] In the TLM method, IV measurements for the different pairs of neighboring electrodes are carried out. It is then possible to determine the resistance values ​​for these different pairs of electrodes as a function of the inter-electrode distance of each of these pairs of electrodes, then to extract the values ​​of the electrical conductivity of the layer of absorber material and the contact resistance between this layer of absorber material and the measuring electrodes.

[0006] The implementation of the TLM method requires the production of conductive measuring electrodes on the surface of the sample to be characterized, these electrodes very often being metallic. This method is generally practiced in the dark. However, the photosensitive layers and contact resistivities of the sample being characterized can be affected by the presence of light excitation. To obtain better accuracy, the electrical characterization of such samples should therefore be carried out under illumination. On the other hand, the measuring electrodes used generate shadowing when the sample is placed under illumination, thus leading to inhomogeneity in the distribution of photo-generated charge carriers in the photovoltaic layer of the sample being studied since the interelectrode distances vary from one pair of measuring electrodes to another. The classical TLM method therefore does not allow obtaining correct results under illumination.

[0007] In the article “In depth analysis of transfer length method application on passivated contacts under illumination” by L. Basset et al., Solar Energy Materials and Solar Cells, Vol. 230, 2021, February 2021, the authors highlight, by numerical simulation and experimental measurements, that inhomogeneities in the spatial concentration of excess minority carriers mainly due to the shadowing of the metal electrodes no longer allow the TLM method to be correctly applied to layers of absorber material based on passivated crystalline silicon for the following reasons: - the resistivity of crystalline silicon is strongly dependent on the density of minority carriers under illumination: for each level of illumination, the resistivity of c-Si must be homogeneous and known; - in the case of simulation results on photovoltaic samples based on n-doped crystalline silicon, it was seen that under an illumination of intensity equal to 1 sun (or 1 sun), i.e. 1000 W / m2, on the front face, no photo-generation occurs under the metal electrodes, thus leading to an inhomogeneity of injected carriers along the axis parallel to the length of the electrodes since these create shading. Along the axis parallel to the thickness of the layer of absorber material, there are also inhomogeneities but these are sufficiently low compared to the thickness of the sample to be homogenized by the diffusion phenomenon.

[0008] When the TLM measurement is carried out under fixed continuous illumination (e.g. under a standardized solar spectrum of type AM 1.5), the average effective shading rate is higher for small inter-electrode distances than for large inter-electrode distances. The photo-generated charge carrier densities are therefore lower for closely spaced electrodes than for electrodes spaced by larger distances. This leads to a variable layer conductivity depending on the pair of electrodes considered, which does not allow the TLM method to be correctly applied when the sample is under illumination. When the photovoltaic sample is illuminated from its rear face (face opposite the front face on which the electrodes are arranged), problems of variability in layer conductivity also appear due to the reflection variations generated by the electrodes. Statement of the invention

[0009] An aim of the present invention is to propose a method for electrical characterization of a photovoltaic sample making it possible to correctly characterize this photovoltaic sample under illumination.

[0010] For this, the invention proposes a method for electrical characterization of a photovoltaic sample comprising at least one stack of layers including a layer of absorber material and measuring electrodes of identical shape and dimensions and arranged on a first face of the photovoltaic sample and forming N pairs of adjacent measuring electrodes having interelectrode distances dr dN different from each other, with N integer greater than or equal to 3, the measuring electrodes of the same pair of adjacent measuring electrodes being parallel to each other, comprising at least:

[0011] a) definition or calculation of a target value R^l<' of layer resistance of the layer of absorber material;

[0012] b) for each pair of adjacent measuring electrode pairs, with inter-electrode distances dt and di+i, with i being an integer between 1 and Nl and such that di+] > di, determination of a value Iu+1 of a light intensity, for a given spectrum illuminating the first face of the photovoltaic sample or a second face, opposite the first face, of the photovoltaic sample, such that a value Rshii+l of sheet resistance (or "Sheet Resistance" in English) of the layer of absorber material, determined by linear interpolation between values ​​^'9 and i^"+! (d of the electrical resistances of said pair of adjacent measuring electrode pairs, is as close as possible to the target value R^le;

[0013] c) determination of a layer resistance value Rsh of the material layer absorber and a contact resistance value Rc of one of the measuring electrodes with the layer of absorber material, by linear interpolation between at least three of the measured values ​​ / j \ and / or pErn Ly ) for the different values ​​lii+1 de-lxpairAui) 1'-pair\ui+y completed in step b).

[0014] Unlike a conventional TLM measurement in which the same illumination (intensity and spectral characteristics) is applied to all areas of the sample subject to the TLM measurement, the proposed method adapts the illumination during the electrical resistance measurements carried out for each pair of adjacent measuring electrode pairs in order to obtain the target value of equivalent layer resistance Rsh or even equivalent electrical resistivity.

[0015] The illumination is adapted by modifying at least the light intensity with which the photovoltaic sample is illuminated.

[0016] This method therefore proposes to voluntarily adjust the illumination of the photovoltaic sample for each of the electrical resistance measurements carried out for each pair of adjacent measuring electrodes, in order to obtain, for the different pairs of adjacent measuring electrodes, the same density of photo-generated carriers, or the same equivalent layer resistance or the same equivalent electrical resistivity, in the layer of absorber material.

[0017] The measurements carried out during step b) make it possible to determine several electrical resistance values ​​for each pair of adjacent measuring electrodes and its adapted illumination.

[0018] Then, the contact resistance and the equivalent layer resistance are calculated, in step c), from the equations of the TLM method, with the electrical resistance values ​​obtained under adapted illumination. This method thus makes it possible to compensate for all or part of the influence of the shadowing of the measuring electrodes (when the sample is illuminated through its first face) and / or the reflections of the illumination on the measuring electrodes (when the sample is illuminated through its second face) which locally modify the density of photo-generated carriers or the equivalent layer resistance in the layer of absorber material.

[0019] The proposed method also provides a relationship, for each pair of measuring electrodes and each inter-electrode zone, between: - the estimated contact resistance and sheet resistance; - the following measurement conditions: dimensions of the measuring electrodes, inter-electrode space, contact face, illumination face; - the illumination applied during the measurements.

[0020] The absorber material may correspond to at least one material which may be a constituent of a photovoltaic component or device, such as for example semi amorphous or crystalline conductor, a transparent conductive oxide, a perovskite material, etc. The absorber material corresponds to a photosensitive material, a light absorber, having conduction properties which vary under illumination thanks to the generation of charge carriers by this illumination.

[0021] The layer(s) of the stack possibly arranged between the face of the sample intended to be illuminated and the layer of absorbing material are such that they allow the passage of at least part of the light spectrum used to illuminate the photovoltaic sample.

[0022] In this method, it is assumed that the contribution of the layers of the stack other than the layer of absorber material to the layer resistance whose target value is defined or calculated in step a) is negligible.

[0023] Throughout the document, the contact resistance Rc of one of the measuring electrodes with the layer of absorber material also includes the electrical resistance of the different layer(s) constituting the electrodes as well as the resistive contributions of the contact resistances between these different layers. The same is true for the specific contact resistivity.

[0024] The measuring electrodes are advantageously of elongated shape.

[0025] In step b), the values ​​and J of the electrical resistances can be measured by an IV measuring device capable of performing IV measurements by injecting a measuring current through two adjacent measuring electrodes and measuring the voltage obtained between these electrodes, or by applying a voltage between two adjacent measuring electrodes and measuring the current flowing between these electrodes. The IV measurements performed to obtain the values ​​1 / - / +1 (a\ and (aj ^pairA u (} lvpair\ui+\ I Electrical resistances can correspond to so-called “4-wire” measurements. The equipment used to carry out these electrical resistance measurements is, for example, a source and measurement unit (SMU).

[0026] The R^,e value can be calculated by TLM method by illuminating the first face of the photovoltaic sample with light whose spectral characteristics and intensity are predetermined.

[0027] Alternatively, the value Re^,le can be chosen by the user within a range of interest to him.

[0028] Alternatively, the value may be obtained as a function of a predetermined value A pcMe of a charge carrier injection rate into the layer of absorber material.

[0029] For example, the value R^le can be obtained as a function of that of A pclhle using the following two equations:

[0030] ~^n(ND + A) + Pp. A p^^ and ç

[0031] with p«We corresponding to the electrical resistivity, in Q.cm, of the layer of absorbing material;

[0032] q corresponding to the elementary charge, in C;

[0033] pn corresponding to the mobility of electrons in the absorbing material, in cm2 / (Vs);

[0034] pp corresponding to the mobility of the holes in the absorber material, in cm2 / (Vs);

[0035] ^corresponding to the density of donor-type charge carriers in the dark in the absorber material, i.e. the concentration of active dopant atoms in the absorber material, in cm3;

[0036] A pcMe corresponding to the predetermined value of the injection rate of target charge carriers into the layer of absorber material, in cm3;

[0037] 7^^ corresponding to the target value of the sheet resistance of the layer of absorber material, in Q / D;

[0038] e corresponding to the thickness of the equivalent layer, i.e. the layer of absorbing material, in cm.

[0039] During step b), the spectral characteristics of the light illuminating the first face of the photovoltaic sample can also be adjusted so that the value Rshil+i of the layer resistance of the layer of absorbing material is as close as possible to the value Thus, the illumination is adapted, during the different measurements of dLm LA and L] \, by modifying the light intensity and also the spectral characteristics of the light illuminating the stack of layers.

[0040] In order for the values ​​of R^le determined from the measurements pL+) [pj and j (d to have a certain precision, the measurement uncertainties of and pLg [p can be much lower, for example by at least a factor of 10, than | • {d- R^A • The measurement uncertainty depends on numerous parameters including the characteristics of the measuring devices but also the precision of the geometry of the measuring electrodes and the difference between the values ​​of d, and di+l.

[0041] The method may further comprise a step d) of determining values ​​of the specific contact resistivity gc and of the transfer length, or distance, LT of the layer of absorber material from the determined values ​​Rsh of layer resistance of the layer of absorber material and Rc of contact resistance of one of the measuring electrodes with the layer of absorber material. The values ​​gc and LT may be obtained by solving the following system of equations:

[0042] R ^lcoth(A)

[0043] pc = Rsh.L^

[0044] with LT corresponding to the transfer length, in cm;

[0045] Pc corresponding to the specific contact resistivity, in Q.cm2;

[0046] W corresponding to the width (dimension “perpendicular” to the direction of the current circulating between two electrodes) of one of the measuring electrodes, in cm;

[0047] L corresponding to the length (dimension “parallel” to the direction of the current flowing between two electrodes) of one of the measuring electrodes, in cm;

[0048] Rsh corresponding to the layer resistance of the layer of absorber material, in Q / D;

[0049] Rc corresponding to the contact resistance of one of the measuring electrodes with the layer of absorbing material, in Q.

[0050] During step b), the values ​​rPmj and can be measured by a IV measuring device (current - voltage).

[0051] The photovoltaic sample may comprise one or more layers of stacked absorber materials, as well as layers of other materials allowing all or part of the light spectrum applied to the absorber material to pass through.

[0052] In a particular configuration, the layer of absorber material may comprise a layer of crystalline semiconductor, the stack of layers may further comprise at least two layers of amorphous semiconductor between which the layer of absorber material is arranged.

[0053] The measuring electrodes may comprise an electrically conductive material, or a stack of several electrically conductive materials.

[0054] In a particular configuration, each of the measuring electrodes may comprise a portion of metal arranged on a portion of transparent conductive oxide.

[0055] The invention also relates to a device for electrical characterization of a photovoltaic sample comprising at least one stack of layers including a layer of absorber material and measuring electrodes of identical shape and size and arranged on a first face of the photovoltaic sample and forming N pairs of adjacent measuring electrodes having inter-electrode distances dj - dN different from each other, with N integer greater than or equal to 3, the measuring electrodes of the same pair of adjacent measuring electrodes being parallel to each other, configured to implement a characterization method as described above.

[0056] This device may in particular comprise an IV measuring device, for example a source and measuring unit SMU, a variable intensity illumination device as well as a calculation unit carrying out the various calculations, linear interpolations, etc., of the process. The illumination device may correspond to a solar simulator or a multi-wavelength light source.

[0057] In this document, the terms “neighbor” and “adjacent” are used interchangeably to describe two measuring electrodes arranged next to each other without a third measuring electrode being arranged between these two measuring electrodes.

[0058] Throughout the document, the term "on" is used without distinction of the orientation in space of the element to which this term relates. For example, in the characteristic "on a face of a layer", this face is not necessarily oriented upwards but can correspond to a face oriented in any direction. Furthermore, the arrangement of a first element on a second element must be understood as being able to correspond to the arrangement of the first element directly against the second element, without any intermediate element between the first and second elements, or as being able to correspond to the arrangement of the first element on the second element with one or more intermediate elements arranged between the first and second elements. Brief description of the drawings

[0059] The present invention will be better understood on reading the description of exemplary embodiments given purely for informational purposes and in no way limiting, with reference to the appended drawings in which:

[0060] [Fig.l] schematically represents an example of a photovoltaic sample electrically characterized during the implementation of the method according to the invention;

[0061] [Fig.2] schematically represents the steps of a method for characterizing a photovoltaic sample, the subject of the present invention;

[0062] [Fig. 3] schematically represents a device for characterizing a photovoltaic sample, also the subject of the present invention.

[0063] The different parts represented in the figures are not necessarily on a uniform scale, in order to make the figures more readable.

[0064] The different possibilities (variants and embodiments) must be understood as not being mutually exclusive and can be combined with each other.

[0065] Detailed description of particular embodiments

[0066] An example of a photovoltaic sample 100 comprising at least one layer of absorber material 112 for which an electrical characterization method under adaptive illumination is implemented is described below in connection with [Fig.l].

[0067] The sample 100 may comprise several layers so that it is structurally close or identical to the layers used in a photovoltaic cell, as shown for example in [Fig.l] in which the sample 100 comprises layers similar to those of a heterojunction photovoltaic cell with passivated contacts. In this [Fig.l], the sample 100 comprises a semiconductor substrate, for example based on n-type crystalline silicon, c-Si(n), and forming the layer of absorber material 112 of the sample 100. The thickness (dimension parallel to the Z axis shown in [Fig.l]) of the layer 112 may be between 40 pm and 400 pm and is for example equal to approximately 160 pm, and the electrical resistivity of the layer 112 is for example close to or equal to 1 Q.cm. The two main faces (front and rear faces parallel to the plane (X,Y) shown in [Fig.l]) of layer 112 are covered by layers 114 and 126 of intrinsic (not intentionally doped) hydrogenated amorphous silicon, a-Si:H(i).The thickness of each of the layers 114 and 126 is sufficient for each of them to form a passivation layer, and may be between 2 nm and 50 nm and is for example equal to 10 nm. The layer 126 located on the side of the rear face of the layer 112 is covered by a layer 116 of p-doped hydrogenated amorphous silicon, a-Si:H(p), and the layer 114 located on the side of the front face of the layer 112 is covered by a layer 118 of n-doped hydrogenated amorphous silicon, a-Si:H(n), so as to form a passivation of the material of the layer 112, make it photoconductive and create a selective contact for the charge carriers. The face of the layer 118 opposite that in contact with the layer 114 forms a first face 106 of the sample 100.

[0068] Alternatively, when the sample 100 comprises layers similar to those of a perovskite photovoltaic cell, the layer of absorber material 112 may comprise a material with a perovskite structure and have a thickness, for example, of between 200 nm and 5 μm. The passivation layers and charge carrier selective layers will be those which are adapted to the perovskite material.

[0069] N pairs of adjacent measuring electrodes, referenced 108.1 to 108.4 in [Fig. 1], are arranged on the first face 106 of the sample 100. Each of these measuring electrodes comprises, for example, a transparent conductive oxide 120, or TCO (“Transparent Conductive Oxide” in English), corresponding, for example, to 1TTO (“Indium Tin Oxide” in English, or indium and tin oxide) and whose thickness is, for example, equal to approximately 100 nm, and a metal layer 122 comprising, for example, silver and whose thickness is, for example, equal to approximately 10 μm, the transparent conductive oxide layer being arranged between the metal layer 122 and the layer 118. The thickness of each measuring electrode (dimension parallel to the Z axis of [Fig. 1]) is, for example, between 100 nm and 50 pm.

[0070] The N pairs of adjacent measuring electrodes, with N integer greater than or equal to 3 and for example between 3 and 11, are arranged on the side on which the sample 100 is illuminated. The number of pairs of electrodes produced on the sample 100 depends in particular on the precision desired for the characterization electrical parameters of sample 100. The greater the number of electrode pairs used, the greater the accuracy of the extraction of the electrical parameters of sample 100.

[0071] Alternatively, the sample 100 may comprise layers of material different from those described for the example above, for example: absence of layers 116 and 118 or layers 114 and 126, replacement of layers 114 and 126 of a-Si:H(i) by different passivation layers such as chemical or thermal oxide layers, covering of layer 116 by a layer of TCO, replacement of the layers of amorphous semiconductor by nanocrystalline or microcrystalline or polycrystalline layers of semiconductor, other type of layer 112 semiconductor, etc.

[0072] In [Fig.l], the sample 100 comprises 4 pairs of adjacent measuring electrodes referenced 108.1, 108.2, 108.3 and 108.4 (i.e. N= 4, N being the number of pairs of adjacent measuring electrodes used for the measurements implemented in the characterization method). Each of the electrodes of the pairs of adjacent measuring electrodes has a shape and dimensions identical to the other electrodes, for example a rectangular shape. Each electrode has for example a length L (dimension parallel to the X axis) between a few tens of microns and a few mm, and a width W (dimension parallel to the Y axis) between (a few mm and a few tens of mm. For example, the width W of each of the measuring electrodes is equal to 15 mm, and the length L of each of the measuring electrodes is equal to 500 μm.

[0073] The measuring electrodes are arranged parallel to their width W (dimension parallel to the Y axis of [Fig.l]). In addition, the measuring electrodes are arranged next to each other so that each pair of electrodes formed by two adjacent electrodes are spaced apart by an inter-electrode distance which varies from one pair of electrodes to the other. Thus, the sample 100 comprises at least 3 pairs of measuring electrodes whose inter-electrode distances are different from each other.

[0074] Each measuring electrode is part of one or two adjacent pairs of measuring electrodes. In the example of [Fig.l], one of the measuring electrodes of the pair of electrodes 108.4 is also part of the pair of measuring electrodes 108.1, and the other of the measuring electrodes of the pair of electrodes 108.4 is also part of the pair of measuring electrodes 108.2. On the other hand, none of the measuring electrodes of the pair of electrodes 108.3 is part of another pair of measuring electrodes.

[0075] In the example of [Fig.l], considering the inter-electrode distance dj of the pair of electrodes 108.1, the inter-electrode distance d2 of the pair of electrodes 108.2, the inter-electrode distance d3 of the pair of electrodes 108.3, the inter-electrode distance d 4 of the pair of electrodes 108.4, these distances are indexed such that dj <d2< d3 < d4, c’est-à-dire telles que dt < di+1 avec i nombre entier compris entre 1 et AM.

[0076] Between two adjacent electrodes of a pair of electrodes 108.i spaced by the distance di, the electrical resistance Rpair(di) measured at the terminals of these two electrodes has the expression: [0077 1

[0078] with Rpair(di): resistance, in Q, measured between the two electrodes of the pair of adjacent measuring electrodes 108.i spaced from each other by the distance dd,

[0079] Rc: contact resistance, in Q, between an electrode of the pair of electrodes 108.i and the layer of absorber material 112;

[0080] Rsh'. sheet resistance, in QO

[0081] Considering the example of [Fig.l], the assumption is made that the amorphous silicon layers 114, 116, 118, 126 have a very high transverse electrical resistivity which can be considered infinite. Considering further that the measuring electrodes are stacks of amorphous layers a-Si:H(i) 114, a-Si:H(n) 118, TCO 120 and metal 122 (for example silver) and that the current passes in the structure only in the crystalline silicon of the layer 112, it is possible to consider that:

[0082] - the contact resistance Rc includes the resistive contribution of the different layers of a-Si:H(i) 114, a-Si:H(n) 118, TCO 120 and metal 122 (silver in the example described above) as well as the contribution of the contact resistances c-Si 112 / a-Si:H(i) 114 (contact resistance between layer 112 and layer 114 arranged on the front side of layer 112), a-Si:H(i) / a-Si:H(n) (contact resistance between layer 114 arranged on the front side of layer 112 and layer 118), a-Si:H(n) / TCO (contact resistance between layer 118 and TCO 120 of the measuring electrodes) and TCO / metal (contact resistance between TCO 120 and metal 122 of the measuring electrodes), and

[0083] - the layer resistance Rsh corresponds to that of layer 112.

[0084] A method for electrical characterization of the photovoltaic sample 100 is described below. The steps of this method are symbolically represented in [Fig.2],

[0085] First, during a step a) designated by the reference 10 in FIG. 2, a target value of layer resistance of the absorber material layer (corresponding to the layer 112 in the sample example 100 previously described) is calculated or chosen.

[0086] According to a first example, the value is obtained by TLM method by illuminating the first face 106 of the sample 100 with a light whose characteristics spectral characteristics and intensity are predetermined (for example a normalized intensity and spectrum such as AM 1.5, also called 1 sun or 1 sun). The predetermined spectral characteristics and intensity may correspond to the desired values ​​for which the user wishes to characterize the sample 100 as precisely as possible. The spectrum of the light used is chosen such that it is compatible with light absorption by the layer of absorbing material 112. A portion of this light spectrum may be absorbed by one or more of the layers located between the light source and the layer of absorbing material 112.

[0087] For the implementation of the TLM method, it is for example possible to choose the 2 pairs of adjacent measuring electrodes whose characteristics are closest to the electrodes of the object studied (for example a photovoltaic cell) and of which the sample 100 is representative, and / or having the inter-electrode distances closest to those of the electrodes of the object studied, and to measure the resistance values ​​Rpair(di) obtained for these pairs of adjacent measuring electrodes. A linear interpolation is then carried out from the curve defined by the measured resistance values ​​Rpair(di). The value is then calculated from the slope / straight line obtained at the end of the linear interpolation carried out, the slope f of this straight line having the expression / ■ _ . J ~ w

[0088] According to a second example, the value Rfble is obtained as a function of a predetermined value A pcible of the charge carrier injection rate in the layer of absorber material. Indeed, from this predetermined value A pclble, it is possible to determine the value which is associated with the charge carrier injection rate A p^^ by the following two equations:

[0089] ~ ( ND + AA p^ and Æ

[0090] with ^ble corresponding to the electrical resistivity, in Q.cm, of the layer of absorbing material;

[0091] q corresponding to the elementary charge, in C;

[0092] pn corresponding to the mobility of electrons in the absorbing material, in cm2 / (Vs);

[0093] pp corresponding to the mobility of the holes in the absorber material, in cm2 / (Vs);

[0094] Nd corresponding to the density of donor-type charge carriers in the dark in the absorber material, i.e. the concentration of active dopant atoms in the absorber material, in cm3;

[0095] A pable corresponding to the predetermined value of the injection rate of target charge carriers into the layer of absorber material, in cm3;

[0096] R^le corresponding to the target value of the sheet resistance of the layer of absorber material, in Q / D;

[0097] e corresponding to the thickness of the equivalent layer, i.e. the layer of absorbing material, in cm.

[0098] The values ​​of the parameters / 4, pp and of the absorber material can be obtained from known technical data according to the absorber material used, or can be measured using existing dedicated instruments known to those skilled in the art. For example, it is possible to estimate the charge carrier density in the absorber material of the sample 100 by carrying out measurements of the electrical resistivity q of the absorber material layer in the dark, for example by a 4-point method or by implementing a conventional TLM method from a few pairs of chosen adjacent measurement electrodes (at least 2 pairs), and then using the following equation to calculate the charge carrier density in the dark:

[0099] -------1------- A'^ / ^ A;,)

[0100] with q corresponding to the elementary charge, in C;

[0101] nn corresponding to the mobility of electrons in the absorbing material, in cm2 / (Vs);

[0102] pp corresponding to the mobility of the holes in the absorber material, in cm2 / (Vs);

[0103] ^corresponding to the density of donor-type charge carriers in the dark in the absorber material, in cm3;

[0104] ^corresponding to the density of acceptor type charge carriers in the absorber material, in cm3 (zero value in the case of an n-type semiconductor layer).

[0105] In the case where the relationship between the charge carrier injection rate A pclble and the light intensity with which the sample 100 is illuminated is known (this relationship can be determined by contactless measurements and by analytical calculations taking into account the light absorption by the sample), it is possible to directly define a light intensity Ictble making it possible to reach the value A pcibie cl therefore gMe

[0106] For example, it is possible to estimate the value of the light intensity IeMe to be applied by calculation to obtain the target charge carrier injection rate A pnble using the following formula:

[0107] fcible „ 0.1 q £. I am

[0108] with q corresponding to the elementary charge, in C;

[0109] e corresponding to the thickness of the equivalent layer, i.e. the layer of absorbing material, in cm;

[0110] A peMe corresponding to the predetermined value of the target charge carrier injection rate, in cm3;

[0111] / "^corresponding to the luminous intensity, in sun, or sun, such that 1 sun = 100 mW / cm2;

[0112] Jsc corresponding to the short-circuit current density, in A / cm2;

[0113] Teff corresponding to the lifetime of the charge carriers, in seconds.

[0114] The value of can be obtained by measurement with equipment marketed under the name WCT-120 by the company Sinton Instruments, on a sample or a cell equivalent to sample 100 in terms of passivation and layers contributing to passivation and absorption of the light spectrum, and without electrodes. The value of Jsc can be obtained either by a measurement IV of photovoltaic cell performance under illumination of r:ible intensity on a sample or a cell equivalent to sample 100 in terms of passivation and layers contributing to passivation and light absorption or by the integration of the spectral response measured over the spectral range of the incident light spectrum.

[0115] After calculating or choosing the value of for each group of two pairs of adjacent measuring electrodes having the inter-electrode distances ch and di+i, with i being an integer between 1 and Nl and di+] > di, a value Iu+1 of a luminous intensity of illumination of the first face of the sample for which a value RShiM of layer resistance of the layer of absorbing material, obtained by linear interpolation between measured values ​​i / «+> [ jj and (pj of the resistances 1Kpaiipuil ^pair^pi+ll electrical between adjacent measuring electrodes having interelectrode distances dt and di+], or as close as possible to the target value is determined (step b) designated by reference 20 in [Fig.2]).

[0116] In sample 100, for the same illumination, the sheet resistance differs between two different pairs of adjacent measuring electrodes due to the amount of illumination, shadows and reflections of the illumination of the patterns of the measuring electrodes which varies as a function of the inter-electrode distance and modifies the injection rate of photo-generated carriers as a function of this inter-electrode distance. The pairs of adjacent measuring electrodes having the closest inter-electrode distances therefore have the closest sheet resistance values ​​for the same illumination.

[0117] In this method, the values ​​of the electrical resistances between the electrodes of the pairs of adjacent measuring electrodes, denoted Rpair(di) for a pair of adjacent measuring electrodes of inter-electrode distance dh are measured using electrical measuring equipment of the SMU (source and measurement unit) type, advantageously by a 4-wire (4W) method. In [Fig.l], the arrows designated by the reference 124 re symbolically present the measuring tips applied to the electrodes when the resistances of the different pairs of electrodes are measured by a 4-wire (4W) method.

[0118] Determining the values ​​liA+1 for which the values ​​RshiM are as close as possible to R^e makes it possible to apply, for each pair of pairs of adjacent measuring electrodes, the illumination leading to obtaining a layer resistance value of the layer of absorbing material which is as close as possible to R^le. This illumination of light intensity value liA+1 can be obtained by different methods, for example by successive tests (preferably around the value lclble or the value of the illumination applied for another pair of pairs of measuring electrodes), or with a scan of the different possible values ​​of the illumination (advantageously a scan with the finest possible step for greater precision).

[0119] During a step c) designated by the reference 30 in FIG. 2, the value Rsh of the layer resistance of the layer of absorber material and the value Rc of the contact resistance of the electrodes with the layer of absorber material are then determined by linear interpolation between the measured values ​​or / ?L+i / i 1 for the different values ​​Iii+1 of the luminous intensity of the light ^pam^i+ij illuminating the first face of the sample. The Rsh value is calculated by determining the slope f of the line obtained by this linear interpolation and using the equation y — , and the Rc value is obtained from the ordinate value at the intersection of the line obtained by this linear interpolation with the ordinate axis which is equal to 2.RC.

[0120] According to a first example, the curve from which this linear interpolation is implemented may correspond to that plotted from the values ​​(jj measured for the pairs of adjacent measuring electrodes 108.z used when the sample 100 is illuminated with the different light intensity values ​​Iu+1. According to a second example, the curve from which this linear interpolation is implemented may correspond to that plotted from the values ​​J with the different values ​​of luminous intensity liA+1.

[0121] Generally speaking, the curve from which this linear interpolation is implemented can correspond to that plotted from all or part of the values ​​\d] and / °u [d- measured for the pairs of adjacent measuring electrodes used when the sample 100 is illuminated with the different values ​​of light intensity Iu+1.

[0122] From the determined values ​​of Rsh and R, it is possible to determine, during a step d) bearing the reference 40 in FIG. 2, the specific contact resistivity Pc and the transfer length LT of the layer of absorber material, which are obtained by solving the following system of equations:

[0123] Æc = 5^coth(A)

[0124] pc = Rsl,Lf

[0125] with LT corresponding to the transfer distance, in cm, and

[0126] Pc corresponding to the specific contact resistivity, in Q.cm2.

[0127] As a variant of the method previously described, during the different steps, it is possible to illuminate a second face, opposite the first face 106, of the photovoltaic sample 100.

[0128] [Fig.3] schematically represents a characterization device 200 of a photovoltaic sample 100 used to implement the characterization method previously described.

[0129] The device 200 comprises a device 202 for measuring IV under illumination making it possible to carry out the various resistance measurements of the pairs of measuring electrodes previously described, for example a source and measurement unit SMU and a solar simulator for illuminating the measurement samples.

[0130] The device 200 also comprises a variable intensity illumination device 203 corresponding for example to a solar simulator.

[0131] The device 200 also comprises a calculation unit 204, for example a computer, making it possible to process the various measurement results and to carry out the calculations of the characterization method described above. This calculation unit 204 can also be used to control the illumination device 203.

Claims

1.

2.

3. Claims Method for electrical characterization of a photovoltaic sample (100) comprising at least one stack of layers (112, 114, 116, 118, 126) including a layer of absorber material (112) and measuring electrodes of identical shape and size and arranged on a first face (106) of the photovoltaic sample (100) and forming N pairs of adjacent measuring electrodes (108.1 - 108.4) having inter-electrode distances dr dN different from each other, with N integer greater than or equal to 3, the measuring electrodes of the same pair of adjacent measuring electrodes (108.1 - 108.4) being parallel to each other, characterized in that it comprises at least: a) definition or calculation (10) of a target value of layer resistance of the layer of absorber material (112); b) for each pair of adjacent measuring electrode pairs (108.1 - 108.4), with inter-electrode distances dt and di+I, with i being an integer between 1 and Nl and such that di+] > dh determination (20) of a value IiA+1 of a luminous intensity, for a given spectrum illuminating the first face (106) of the photovoltaic sample (100) or a second face, opposite the first face, of the photovoltaic sample (100), such that a value Rshil+1 of layer resistance of the layer of absorber material (112), determined by linear interpolation between values p1' ) (aj and p1^ (a \ of the resistances ^pair^i} 1'-pairAu i+ll electrical of said pair of adjacent measuring electrode pairs, as close as possible to the target value R^le; c) determining (30) a value Rsh of layer resistance of the layer of absorber material (112) and a value Rc of contact resistance of one of the measuring electrodes with the layer of absorber material (112), by linear interpolation between at least three of the measured values of resistance p1^ LA and / or pL+> (a ) for the dif-lvpatn\ui] ^pair^i+AJ different IiA+1 values determined in step b). The method of claim 1, wherein the R^^le value is calculated by TLM method by illuminating the first face (106) of the photovoltaic sample (100) with light whose spectral characteristics and intensity are predetermined. The method of claim 1, wherein the value R^le is obtained depending on a predetermined value A pc,ble of a charge carrier injection rate into the layer of absorber material (112).

4. Method according to one of the preceding claims, in which, during step b), the spectral characteristics of the light illuminating the first face (106) of the photovoltaic sample (100) are also adjusted so that the value Rsh^ of sheet resistance of the layer of absorber material (112) is as close as possible to the value R^1^. ^sh

5. Method according to one of the preceding claims, in which the values r^m. / p\et jJü+ij are measured, during step b), with ^pair^ij ^pam\ai+l) r measurement uncertainties much lower than lr!-' [. / \ r1^ ij . 11 '■pairA™ i+1J 1 vpair\ui / j

6. Method according to one of the preceding claims, further comprising a step d) of determining values of the specific contact resistivity qc and of the transfer length LT of the layer of absorber material (112) from the determined values Rsh of layer resistance of the layer of absorber material (112) and Rc of contact resistance of one of the measuring electrodes with the layer of absorber material (112).

7. Method according to one of the preceding claims, in which, during step b), the values and J are measured by a measuring device IV (202).

8. Method according to one of the preceding claims, in which the layer of absorber material (112) comprises a layer of crystalline semiconductor, the stack of layers further comprising at least two layers of amorphous semiconductor (114, 116, 118, 126) between which the layer of absorber material (112) is arranged.

9. Method according to one of the preceding claims, in which each of the measuring electrodes comprises a portion of metal (122) arranged on a portion of transparent conductive oxide (120).

10. Device (200) for electrical characterization of a photovoltaic sample (100) comprising at least one stack of layers (112, 114, 116, 118, 126) including a layer of absorber material (112) and measuring electrodes of identical shape and size and arranged on a first face (106) of the photovoltaic sample (100) and forming N pairs of adjacent measuring electrodes (108.1 -108.4) having different inter-electrode distances dj - dN from each other, with N integer greater than or equal to 3, the measuring electrodes of the same pair of adjacent measuring electrodes (108.1 - 108.4) being parallel to each other, configured to implement a characterization method according to one of the preceding claims.

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