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 surface density of photoluminescence of the regions of the sample between the electrodes; b) for each pair of adjacent electrodes, determining a value of an illumination intensity such that a value of the surface density of photoluminescence between the electrodes is as close as possible to; c) for each pair of adjacent electrodes, measuring an electrical resistance between the electrodes with an illumination intensity; d) determining a value R Sh of the layer resistance of the absorber material layer and a value R c of the contact resistance of one of the electrodes with the absorber material layer, by linear interpolation (TLM method) between at least two of the values. Figure for the abbreviation: figure 1.

Description

Title of the invention: METHOD FOR ELECTRICAL CHARACTERIZATION OF AN ABSORBENT MATERIAL UNDER VARIABLE ILLUMINATION technical field

[0001] The invention relates to the field of electrical characterization of an absorber material, that is, a photovoltaic conversion material suitable for use in the production of photovoltaic cells. The invention can be used, for example, to characterize high-performance crystalline silicon-based photovoltaic structures with passivated contacts. In particular, the invention can be used to determine the resistive losses obtained in operating photovoltaic cells, that is, under illumination, made with the absorber material thus characterized. Prior art

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

[0003] Current-voltage measurements (IV measurements), in darkness or under illumination, are commonly used to evaluate the performance of photovoltaic cells or elements thereof, and to understand the phenomena underlying certain limitations in cell performance. Such an IV measurement applied to a photovoltaic cell consists of measuring the electric current delivered by the cell while applying an electric voltage across 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 (TLM), also known as the transfer length method, allows for the determination of the conductivity of a material layer and the contact resistivity between this material layer and conductive measuring electrodes formed on this material layer. This method is implemented using a photovoltaic sample comprising at least one layer of absorber material (the same as that used to manufacture the photovoltaic cell) on which several conductive measuring electrodes are arranged. The measuring electrodes are, for example, elongated, arranged parallel to each other, and spaced at 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 another. These distances are called inter-electrode distances.

[0005] In the TLM method, IV measurements are performed for the different pairs of neighboring electrodes. 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, and then to extract the values ​​of the electrical conductivity of the absorption material layer and the contact resistance between this absorption material layer and the measuring electrodes.

[0006] The implementation of the TLM method requires the use of conductive measuring electrodes on the surface of the sample to be characterized; these electrodes are very often metallic. This method is generally carried out in the dark. However, the photosensitive layers and contact resistivities of the characterized sample can be affected by the presence of light excitation. Therefore, to obtain better accuracy, the electrical characterization of such samples should be performed under illumination. However, the measurement electrodes used generate shadowing when the sample is placed under illumination, leading to inhomogeneity in the distribution of photogenerated charge carriers in the photovoltaic layer of the sample under study, since the interelectrode distances vary from one pair of measurement electrodes to another. The classical TLM method therefore does not allow for obtaining accurate 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, through numerical simulation and experimental measurements, that inhomogeneities in the spatial concentration of excess minority carriers, mainly due to shading of the metallic electrodes, no longer allow the TLM method to be correctly applied to layers of passivated crystalline silicon-based absorber material for the following reasons: - the resistivity of crystalline silicon is strongly dependent on the minority carrier density under illumination: for each level of illumination, the resistivity of c-Si must be homogeneous and known; - In the case of simulation results on n-doped crystalline silicon photovoltaic samples, it was observed that under an irradiance equal to one sun (1000 W / m²), no photogeneration occurs on the front surface under the metallic electrodes. This leads to inhomogeneity of injected charge carriers along the axis parallel to the electrode length, as the electrodes create shading. Inhomogeneities also exist along the axis parallel to the thickness of the absorber layer, but these are sufficiently small compared to the sample thickness to be homogenized by diffusion.

[0008] When the TLM measurement is performed under a fixed continuous illumination (for example, under a standardized AM 1.5 solar spectrum), the average effective shading ratio is higher for small inter-electrode distances than for large inter-electrode distances. The densities of photogenerated charge carriers are therefore lower for closely spaced electrodes than for electrodes spaced at greater distances. This leads to a variable layer conductivity depending on the electrode pair considered, which prevents the TLM method from being applied correctly when the sample is under illumination. When the photovoltaic sample is illuminated from its back side (the side opposite the front side on which the electrodes are arranged), layer conductivity variability problems also arise due to variations in reflection caused by the electrodes. Description of the invention

[0009] An object of the present invention is to propose a method for electrical characterization of a photovoltaic sample allowing to properly characterize this photovoltaic sample under illumination.

[0010] To this end, the invention proposes a method for the 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 arranged on a first face of the photovoltaic sample and forming N pairs of adjacent measuring electrodes having different inter-electrode distances dr dN, with N an integer greater than or equal to 2, the measuring electrodes of the same pair of adjacent measuring electrodes being parallel to each other, comprising at least: a) definition or calculation of a target value eMe of surface density of a photoluminescence signal intended to be emitted from regions of the photovoltaic sample located between the measuring electrodes of each of the N pairs of adjacent measuring electrodes; b) for each of the N pairs of adjacent measuring electrodes, with inter-electrode distance di, where i is an integer between 1 and A, determination of a value j, a luminous intensity, for a given SPL spectrum illuminating a face, corresponding to the first face of the photovoltaic sample or to a second face, opposite to the first face, of the photovoltaic sample, such that a value dPL of surface density of a photoluminescence signal emitted from the region of the photovoltaic sample located between the adjacent measuring electrodes having the inter-electrode distance dh is as close as possible to the target value ■ c) for each of the N pairs of adjacent measuring electrodes, with inter-electrode distance dt, measurement of an electrical resistance between the electrodes of adjacent measurements showing the inter-electrode distance dh during illumination of said face of the photovoltaic sample with the SPL spectrum applied with the light intensity; d) determination of a layer resistance value Rsh of the absorber material layer and a contact resistance value Rc of one of the measuring electrodes with the absorption material layer, by linear interpolation between at least two of the values ​​measured in step c).

[0011] Unlike a conventional TLM measurement in which the same illumination (intensity and spectral characteristics) is applied to all areas of the sample being measured, the proposed method adapts the illumination during the electrical resistance measurements performed for each of the N pairs of adjacent measuring electrodes in order to obtain a surface density value of the photoluminescence signal emitted from the regions of the photovoltaic sample located between the electrodes of each of the N pairs of adjacent measuring electrodes that is as close as possible to the defined target value cMe or calculated prior to the measurements.

[0012] The illumination is adapted by modifying the luminous intensity with which The photovoltaic sample is illuminated during resistance measurements. electric r pair between the measuring electrodes for each of the pairs measuring electrodes.

[0013] 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, an identical or almost identical surface density of generated photoluminescence signal, or an identical or almost identical density of photo-generated carriers, or an identical or almost identical equivalent layer resistance or equivalent electrical resistivity, in the absorbing material layer.

[0014] The contact resistance and the equivalent layer resistance can be calculated, in step d), from the equations of the TLM method, using the electrical resistance values ​​obtained under illumination adapted in step c). This method thus makes it possible to compensate for all or part of the influence of shading of the measuring electrodes (when the sample is illuminated through its first face) and / or 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 absorber material layer.

[0015] The proposed method also provides a relationship, for each pair of measuring electrodes and each inter-electrode zone, between: - the estimated contact resistance and layer resistance; - the photoluminescent signal density; - the following measurement conditions: dimensions of the measuring electrodes, inter-electrode space, contact face, illumination face; - the illumination applied during the measurements.

[0016] The absorber material may correspond to at least one material that can be a constituent of a photovoltaic component or device, such as, for example, an amorphous or crystalline semiconductor, a transparent conductive oxide, a perovskite material, etc. The absorber material corresponds to a photosensitive material, a light absorber, having conduction properties that vary under illumination due to the generation of charge carriers by this illumination.

[0017] The layer(s) of the stack possibly arranged between the face of the sample intended to be illuminated and the absorbing material layer are such that that they allow the passage of at least part of the SPL light spectrum used to illuminate the photovoltaic sample.

[0018] In this process, it is assumed that the contribution of the stacking layers other than the absorber material layer to the surface density of the photoluminescence signal intended to be emitted from the regions of the photovoltaic sample located between the measuring electrodes of each of the N pairs of adjacent measuring electrodes, whose target value ^PL able is defined or calculated in step a), is negligible.

[0019] Throughout the document, the contact resistance Rc of one of the electrodes of measurement with the absorbent material layer also includes the electrical resistance of the or the different layers constituting the electrodes as well as the contributions re sistive contact resistances between these different layers. The same applies to the specific contact resistivity.

[0020] The measuring electrodes are advantageously elongated in shape.

[0021] In step c), the values fpair -dPLal electrical resistances can be measured by a measuring device IV capable of performing IV measurements by injecting a measurement current through two adjacent measuring electrodes and by measuring the voltage obtained between these electrodes, or by applying a voltage between two adjacent measuring electrodes and by measuring the current flowing between these Electrode measurements were performed to obtain the values. D- Electrical resistances can correspond to so-called "4-wire" measurements. The equipment used to perform these electrical resistance measurements is, for example, a source and measurement unit (SMU).

[0022] The target value d^L cihle can be calculated from a target value Rs'£le of layer resistance of the absorber material layer or from a target value A of a charge carrier injection rate in the absorber material layer.

[0023] In particular, the value can be calculated by TLM method by illuminating said first face of the photovoltaic sample with light whose spectral characteristics and intensity are predetermined and of interest, or the value can be predefined, i.e. chosen by use within a range of interest for it.

[0024] Alternatively, the value can also be obtained by calculation from the target value A pclble-

[0025] According to another embodiment, the target value dPL clble can be defined from a photoluminescence measurement of a value dCL by illuminating the photovoltaic sample (100) with light whose spectral characteristics and intensity are predetermined; the illumination of the photovoltaic sample and the photoluminescence measurement are carried out on said first face.

[0026] According to another embodiment, the target value clh,e can also be predefined or chosen.

[0027] Indeed, the photoluminescence signal density dbL emitted from the region of the photovoltaic sample located between adjacent measuring electrodes with inter-electrode distance dt can be expressed by the equation: d^L = Kjzp, with K: optical constant whose value depends on the properties of the illumination equipment of the photovoltaic sample used and of a measurement equipment of the photoluminescence signal used, as well as of the photovoltaic sample (presence or absence of textures, anti-reflective layers, resolution of the equipment, etc.); n: the free electron density, expressed by the equation n = ND + An^ with ND corresponding to the density of donor-type charge carriers in the dark in the absorbing material, in cm3, and An corresponding to the density of electrons generated in excess under light in the absorbing material; p: the free hole density, expressed by the equation P = NA + Ap, where NA corresponds to the density of acceptor-type charge carriers in the absorber material, in cm³, and has a value of zero in the case of an n-type semiconductor layer, and Ap corresponds to the density of excess electrons generated under light in the absorbent material.

[0028] When the absorber material of the photovoltaic sample is an n-type semiconductor, and by illuminating the photovoltaic sample in a light excitation range such that An = Ap, the measured photoluminescence signal density dPL can therefore be expressed by the equation: dPP = K.(ND + Ap).Ap

[0029] For a given sample and illumination and measurement equipment, the values ​​of K and ND are constant. The photoluminescence measurements of the sample can therefore be viewed as measurements of the Ap parameter in the absorber material, which directly affect the layer resistance value of the absorber material layer.

[0030] If the measured value of the cell is constant from one pixel to another or from one group of pixels to another of the measurement specimen, this means that the value of the parameter Ap is constant for these pixels or these different groups of pixels.

[0031] The dPL value of surface density of the photoluminescence signal emitted from the region of the photovoltaic sample located between the adjacent measuring electrodes having the inter-electrode distance di, can be defined as the sum of the photoluminescent signal measured on the surface of interest which corresponds to the surface equal to the width of the electrodes (i.e. the parallel side of the electrodes 2 to 2) multiplied by the inter-electrode distance d;.

[0032] The target value of the photoluminescence measurement can be calculated from the value of ND, the constant K, and the target value of the photovoltaic sample. In this case, the value of ND can be obtained by a 4-point or TLM measurement in the dark. The value of K can be determined by calibrating the measurement system using photoluminescence for each type of photovoltaic sample (the constant K depends on the light transmission to the absorber material).

[0033] Furthermore, and according to an example of implementation, the value can be obtained as a function of that of a pcMe using the following two equations: 7~k ~ ( Nd + A Pcible ) + Pp-A and ^le = with pcible corresponding to the electrical resistivity, in Q.cm, of the absorption material layer; q corresponding to the elementary charge, in C; pn corresponding to the mobility of electrons in the absorbing material, in cm2 / (Vs); pp corresponding to the mobility of the holes in the absorbing material, in cm2 / (Vs); ^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; A pcîbie corresponding to the predetermined value of the target charge carrier injection rate in the absorber material layer, in cm3; R^le corresponding to the target value of the layer resistance of the absorber material layer, in Q / D; e corresponds to the thickness of the equivalent layer, i.e., the absorbing material layer, in cm. In step b), the photoluminescence signal can be measured by a photoluminescence measuring device. This photoluminescence measuring device may include at least one CCD sensor.

[0034] Step a) can be implemented by illuminating the photovoltaic sample and measuring the photoluminescence signal emitted from one of the regions of the photovoltaic sample located between the measuring electrodes of each of the A pairs of adjacent measuring electrodes. During step a), the photovoltaic sample can be illuminated by a solar simulator.

[0035] Step b) can be implemented: - by mapping, using the SPL spectrum and under Icarto intensity illumination, the surface density of the photoluminescence signal d^L(Icarto) of the photovoltaic sample (100) between each of the A pairs of adjacent measuring electrodes (108.1 - 108.4), and by calculating the different values ​​of idPLcMe allowing obtaining the same value clb,e between each pair of electrodes such that hano Or - by successive trials or by scanning different possible values ​​of idPLc,ble

[0036] The surface density value of the photoluminescence signal emitted from the region of the photovoltaic sample located between the adjacent measuring electrodes having the inter-electrode distance dt can be measured by measuring the photoluminescence signal emitted from the region of the photovoltaic sample located between the adjacent measuring electrodes having the inter-electrode distance dh and by calculating the surface density value of the photoluminescence signal measured emitted from the region of the photovoltaic sample located between the adjacent measuring electrodes having the inter-electrode distance dt;

[0037] a certain degree of precision, the uncertainties of measurements of hideout K^PL target may be much lower, for example by at least a factor of 10, than । ^pair IK^PL target ^i+1) j^pair K ^PL target j. Measurement uncertainty depends on many factors ramometers whose characteristics of the measuring devices but also of the precision of the geometry of the measuring electrodes and of the difference between the values ​​of d{ and di+i.

[0038] The method may further include a step e) of determining the values ​​of the specific contact resistivity qc and the transfer length, or distance, LT of the absorber material layer from the determined values ​​Rsh of the layer resistance of the absorber material layer and Rc of the contact resistance of one of the Measuring electrodes with the absorber material layer. The qc and LT values ​​can be obtained by solving the following system of equations: Rc — "3F coth(

[0039] with LT corresponds to the transfer length, in cm; Pc corresponds to the specific contact resistivity, in Q.cm2; IV corresponding to the width (dimension "perpendicular" to the direction of the current flowing between two electrodes) of one of the measuring electrodes, in cm; 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; Rsh corresponds to the layer resistance of the absorber material layer, in Q / D (Ohm per square); Rc corresponds to the contact resistance of one of the measuring electrodes with the absorption material layer, in Q.

[0040] During step c), the values ​​can be measured by a device measurement IV (current - voltage).

[0041] 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 SPL light spectrum applied to the absorber material to pass through.

[0042] In a particular configuration, the absorber material layer may include a crystalline semiconductor layer, the stacking of layers may further include at least two amorphous semiconductor layers between which the absorber material layer is arranged.

[0043] The measuring electrodes may comprise an electrically conductive material, or a stack of several electrically conductive materials.

[0044] In a particular configuration, each of the measuring electrodes can comprising a portion of metal arranged on a portion of conductive transparent oxide.

[0045] The invention also relates to an electrical characterization device for a photovoltaic sample comprising at least one stack of layers including a layer of absorber material and measuring electrodes of identical shape and size arranged on a first face of the photovoltaic sample and forming N pairs of adjacent measuring electrodes having different inter-electrode distances dj - dN from each other, with N an integer greater than or equal to 2, 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.

[0046] This device may include, in particular, a measurement device IV, for example a source and measurement unit SMU, a variable intensity illumination device, and a computing unit performing the various calculations, linear interpolations, etc., of the process. The illumination device may be a solar simulator or a multi-wavelength light source.

[0047] Advantageously, the measurements of the photoluminescence signal can be carried out by a measuring device having a light source suitable for such measurements, for example a laser emitting light whose wavelength is well suited to cause the phenomenon of photoluminescence in the absorbing material (emitting for example light with a wavelength of 915 nm when the absorbing material is crystalline silicon).

[0048] Alternatively, the light source used during the measurements of the photoluminescence signal can be the same as that used to illuminate the photovoltaic sample during step a).

[0049] Regardless of the embodiment or variant considered, the illumination of the photovoltaic sample can be carried out on the first or second face of the sample. Similarly, the photoluminescence signal measurements can be carried out from the first or second face of the sample (regardless of the illuminated face). However, the face from which the photoluminescence measurements are carried out remains unchanged for steps a) and b) if photoluminescence measurements are carried out in step a). The illuminated face remains unchanged during steps b) and c) of the characterization process.

[0050] 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.

[0051] Throughout the document, the term "on" is used without distinction of The spatial orientation of the element to which this term refers. 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 should be understood as either having the first element directly against the second element, without any intermediate elements between the first and second elements, or having 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

[0052] The present invention will be better understood upon reading the description of exemplary embodiments given by way of illustration only and in no way limiting, with reference to the accompanying drawings in which: [Fig.l] schematically represents an example of a photovoltaic sample characterized electrically during the implementation of the process according to the invention; [Fig.2] schematically represents the steps of a process for characterizing a photovoltaic sample, the subject of the present invention; [Fig.3] schematically represents a device for characterizing a photovoltaic sample, which is also the subject of the present invention.

[0053] The different parts represented in the figures are not necessarily shown on a uniform scale, in order to make the figures more legible.

[0054] The different possibilities (variants and embodiments) should be understood as not being mutually exclusive and can be combined with each other.

[0055] Detailed description of particular embodiments

[0056] An example of a photovoltaic sample 100 comprising at least one layer of absorber material 112 for which an electrical characterization process under adaptive illumination is implemented is described below in relation to [Fig.1].

[0057] The sample 100 may comprise several layers so that it is structurally similar or identical to the layers used in a photovoltaic cell, as shown, for example, in [Fig. 1], in which the sample 100 comprises layers similar to those of a heterojunction photovoltaic cell with passivated contacts. In this [Fig. 1], the sample 100 comprises a semiconductor substrate, for example, based on n-type crystalline silicon, c-Si(n), forming the absorber material layer 112 of the sample 100. The thickness (dimension parallel to the Z-axis shown in [Fig. 1]) of the layer 112 may be between 40 pm and 400 pm and is, for example, approximately 160 pm, and the electrical resistivity of the layer 112 is, for example, close to or equal to 1 Ω·cm. The two main faces (front and rear faces parallel to the (X,Y) plane shown in [Fig. 1]) of layer 112 are covered by layers 114 and 126 of intrinsic hydrogenated amorphous silicon (unintentionally doped), 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 can be between 2 nm and 50 nm and is, for example, equal to 10 nm. Layer 126, located on the back side of layer 112, is covered by a layer 116 of p-doped hydrogenated amorphous silicon, a-Si:H(p), and layer 114, located on the front side of layer 112, is covered by a layer 118 of n-doped hydrogenated amorphous silicon, a-Si:H(n), so as to passivate the material of layer 112, making it photoconductive and creating a selective contact for charge carriers. The face of layer 118 opposite the face in contact with layer 114 forms a first face 106 of sample 100.The face of layer 116 opposite to that in contact with layer 126 forms a second face 107 of sample 100, corresponding to a back face of sample 100.

[0058] Alternatively, when the sample 100 comprises layers similar to those of a perovskite photovoltaic cell, the absorber material layer 112 may comprise a perovskite-structured material and have a thickness, for example, between 200 nm and 5 pm. The passivation layers and charge carrier-selective layers will be those adapted to the perovskite material.

[0059] 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), corresponding, for example, to 1TTO (Indium Tin Oxide) and whose thickness is, for example, approximately 100 nm, and a metallic layer 122 comprising, for example, silver and whose thickness is, for example, approximately 10 pm, the transparent conductive oxide layer being arranged between the metallic 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.

[0060] The N pairs of adjacent measuring electrodes, with N being an integer greater than or equal to 2 and for example between 2 and 11, are arranged on the first face 106 of sample 100. The number of electrode pairs made on sample 100 depends in particular on the desired precision for the electrical characterization of sample 100. The greater the number of electrode pairs used, the greater the precision of the extraction of the electrical parameters of sample 100.

[0061] Alternatively, sample 100 may comprise different material layers than 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) with different passivation layers such as chemical or thermal oxide layers, covering of layer 116 with a TCO layer, replacement of amorphous semiconductor layers with nanocrystalline or microcrystalline or polycrystalline semiconductor layers, other type of semiconductor layer 112, etc.

[0062] In [Fig. 1], sample 100 comprises 4 pairs of adjacent measuring electrodes, referenced 108.1, 108.2, 108.3, and 108.4 (i.e., N = 4, where N is the number of pairs of adjacent measuring electrodes used for the measurements implemented in the characterization process). Each electrode in the pairs of adjacent measuring electrodes has the same shape and dimensions as the other electrodes, for example, a rectangular shape. Each electrode has, for example, a length L (dimension parallel to the X-axis) of between a few tens of microns and a few millimeters, and a width W (dimension parallel to the Y-axis) of between a few millimeters and a few tens of millimeters. As an example, the width W of each measuring electrode is 15 mm, and the length L of each measuring electrode is 500 µm.

[0063] The measuring electrodes are arranged parallel to their width W (dimension parallel to the Y-axis of [Fig. 1]). Furthermore, the measuring electrodes are arranged side by side such that each pair of electrodes, formed by two adjacent electrodes, is separated by an inter-electrode distance that varies from one pair of electrodes to the other. Thus, sample 100 comprises at least two pairs of measuring electrodes with different inter-electrode distances.

[0064] Each measuring electrode is part of one or two pairs of adjacent measuring electrodes. In the example of [Fig. 1], one of the measuring electrodes of electrode pair 108.4 is also part of measuring electrode pair 108.1, and the other of the measuring electrodes of electrode pair 108.4 is also part of measuring electrode pair 108.2. On the other hand, none of the measuring electrodes of electrode pair 108.3 is part of another measuring electrode pair.

[0065] In the example of Figure 1, considering the inter-electrode distance dj of electrode pair 108.1, the inter-electrode distance d2 of electrode pair 108.2, the inter-electrode distance d3 of electrode pair 108.3, and the inter-electrode distance d4 of electrode pair 108.4, these distances are indexed such that dj <d2< d3 < d4, c’est-à-dire telles que d j < d j+\ avec j nombre entier compris entre 1 et A-l.

[0066] Between two adjacent electrodes of a pair of electrodes 108.i separated by a distance dh, the electrical resistance Rpaire(di) measured across the terminals of these two electrodes has the following expression: with Rpaire(dd : resistance, in Q, measured between the two electrodes of the pair of adjacent measuring electrodes 108.i spaced apart by a distance d^ Rc: contact resistance, in Q, between an electrode of the electrode pair 108.i and the absorber material layer 112; Rsh-. layer resistance, in Q / D (Ohm / square).

[0067] Considering the example in [Fig. 1], it is assumed that the amorphous silicon layers 114, 116, 118, 126 exhibit 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 flows through the structure only in the crystalline silicon of layer 112, it is possible to consider that: - 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 on the front side of layer 112), a-Si:H(i) / a-Si:H(n) (contact resistance between layer 114 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) measuring electrodes), and - the layer resistance Rsh corresponds to that of layer 112.

[0068] A method for the electrical characterization of the photovoltaic sample 100 is described below. The steps of this method are symbolically represented in [Fig. 2].

[0069] First, during a step a) designated by reference 10 in Figure 2, a target value Clb!e of surface density of a photoluminescence signal intended to be emitted from regions of the photovoltaic sample 100 located between the measuring electrodes of each of the N pairs of adjacent measuring electrodes 108.1-108.4 is calculated (from data itself chosen or measured or calculated) or chosen.

[0070] According to a first example, the target value A pcMe can be defined directly from a measurement of a dsL value by illuminating the first face 106 or the second face 107 of the sample 100 with light, for example emitted by a solar simulator, whose spectral characteristics and intensity are predetermined (for example, a standardized intensity and spectrum such as AM 1.5, also called 1 sun). The predetermined spectral characteristics and intensity can correspond to the desired values ​​for which the user wishes to characterize sample 100 as precisely as possible. The spectrum of the light used is chosen so that it is compatible with light absorption by the absorber material layer 112. Part of this light spectrum may be absorbed by one or more of the layers located between the light source and the absorber material layer 112.

[0071] Alternatively, the target value can be predefined, i.e. chosen by the user from a range of interest to him.

[0072] According to a second example, the value d^L is obtained by calculation from a value ^lble of layer resistance itself obtained by the TLM method by illuminating the first face 106 or the second face 107 of the sample 100 with light, for example emitted by a solar simulator, whose spectral characteristics and intensity are predetermined (for example, a normalized intensity and spectrum such as AM 1.5, also called 1 sun). The predetermined spectral characteristics and intensity can 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 absorber material layer 112. Part of this light spectrum can be absorbed by one or more of the layers located between the light source and the absorber material layer 112.

[0073] For the implementation of the TLM method, it is possible, for example, to choose the two pairs of adjacent measuring electrodes whose characteristics most closely resemble those of the electrodes of the object under study (for example, a photovoltaic cell) and of which sample 100 is representative, and / or having inter-electrode distances closest to those of the electrodes of the object under study, and to measure the resistance values ​​Rpair(di) obtained for these pairs of adjacent measuring electrodes. A linear interpolation is then performed from the curve defined by the measured resistance values ​​Rpair(dt). The value Rble is then calculated from the slope of the line obtained at the end of the linear interpolation, the slope of this line being expressed as _ A". J “ ü

[0074] According to one variant, the value of d?L clble is obtained by calculation from a predefined or chosen layer resistance value R™hie.

[0075] According to one embodiment, the value d^L is obtained by calculation from a value A pc,bte of the charge carrier injection rate in the material layer chosen or predetermined absorber.

[0076] According to a third example, the value dPL able is obtained by calculation from a value ap,:ible of the charge carrier injection rate in the chosen or predetermined absorbing material layer.

[0077] It is possible to determine from and to determine from of A pcMe using the following equations and under the following assumptions.

[0078] Indeed, from this predetermined value A, it is possible to determine the value associated with the charge carrier injection rate A pcMe by the following two equations: with pable corresponding to the electrical resistivity, in Q.cm, of the absorption material layer; q corresponding to the elementary charge, in C; pn corresponding to the mobility of electrons in the absorbing material, in cm2 / (Vs); pp corresponding to the mobility of holes in the absorber material, in cm2 / (Vs); Nd corresponding to the density of dark-type donor charge carriers in the absorber material, i.e. the concentration of active dopant atoms in the absorber material, in cm3; A pcMe corresponding to the predetermined value of the target charge carrier injection rate in the absorber material layer, in cm3; corresponding to the target value of the layer resistance of the absorber material layer, in Q / D (Ohm / square); e corresponding to the thickness of the equivalent layer, i.e. the absorbing material layer, in cm.

[0079] The values ​​of the parameters pn, pp, and ND of the absorber material can be obtained from known technical data specific 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 ND in the absorber material of sample 100 by performing measurements of the electrical resistivity q of the absorber material layer in the dark, for example, by a four-point method or by implementing a conventional TLM method using a few selected pairs of adjacent measuring electrodes (at least two pairs), and then using the following equation to calculate the charge carrier density ND in the dark: *7>+ fjp N 4)

[0080] with q corresponding to the elementary charge, in C; Hn corresponding to the mobility of electrons in the absorbing material, in cm2 / (Vs); pp corresponding to the mobility of the holes in the absorbing material, in cm2 / (Vs); Nd corresponds to the density of donor-type charge carriers in the dark in the absorber material, in cm3; Na corresponds to the density of acceptor-type charge carriers in the absorber material, in cm3 (of zero value in the case of an n-type semiconductor layer).

[0081] In the case where the relationship between the charge carrier injection rate a pcible and the light intensity with which the sample 100 is illuminated is known (this relationship being able to be determined by non-contact measurements and by analytical calculations taking into account the light absorption by the sample), it is possible to directly define a light intensity jc^Lc,ble allowing the value to be reached 1 i A ptarget C( clonc R^ble then clhle.

[0082] For example, it is possible to estimate the value of the light intensity to be applied by calculation to obtain the target charge carrier injection rate Apcible using the following formula: Td^Ll"Me _ 04 ? ^pah!e Î ~ Jst with q corresponding to the elementary charge, in C; e corresponding to the thickness of the equivalent layer, i.e. the absorbing material layer, in cm; A pcible corresponding to the predetermined value of the target charge carrier injection rate, in cm3; corresponding to light intensity, in suns, such that 1 sun = 100 mW / cm2; Jsc corresponding to the short-circuit current density, in A / cm2; Teff corresponds to the lifetime of the load carriers, in seconds.

[0083] The value of t,,B can be obtained by measurement with equipment marketed under the name WCT-120 by the company Sinton Instruments, on a sample or 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 an IV measurement of photovoltaic cell performance under illumination of intensity jd^LcMe on a sample or a cell equivalent to the sample 100 in terms of passivation and layers contributing to passivation and light absorption or by integrating the spectral response measured over the spectral range of the incident light spectrum.

[0084] Alternatively, it is possible to calculate the target value c,ble from a value of the target charge carrier injection rate A pable itself calculated from photoluminescence signals measured on sample 100.

[0085] Indeed, the photoluminescence signal density emitted from the region of the photovoltaic sample 100 located between adjacent measuring electrodes having the inter-electrode distance dt can be expressed by the equation: = Kji.p, with K: optical constant whose value depends on the properties of the illumination equipment of the photovoltaic sample 100 used and of a photoluminescence signal measurement equipment used, as well as of the photovoltaic sample 100 (presence or absence of textures, anti-reflective layers, resolution of the equipment, etc.); n: the free electron density, expressed by the equation n = ND + An^ with ND corresponding to the density of donor-type charge carriers in the dark in the absorbing material, in cm3, and An corresponding to the density of electrons generated in excess under light in the absorbing material; p: the free hole density, expressed by the equation P = NA + Ap, with NA corresponding to the density of acceptor-type charge carriers in the absorber material, in cm3, and of zero value in the case of an n-type semiconductor layer, and Ap corresponding to the density of electrons generated in excess under light in the absorber material.

[0086] When the absorber material of the photovoltaic sample 100 is an n-type semiconductor, and illuminating the photovoltaic sample in a light excitation range such that An = Ap, the measured photoluminescence signal density d^L can therefore be expressed by the equation: d^=K\ND + Ap).Ap

[0087] For a given sample of 100 and illumination and measurement equipment, the values ​​of K and ND are constant. The photoluminescence measurements of the sample can therefore be seen as measurements of the parameter Ap in the absorber material and which directly affect the value of the layer resistance of the absorbing material layer. If the measured value dPL cihle is constant from one pixel to another or from one group of pixels to another in the measurement specimen, this means that the value of the parameter Ap is constant for these pixels or these different groups of pixels.

[0088] The surface density value of the photoluminescence signal emitted from the region of the photovoltaic sample located between the adjacent measuring electrodes having the inter-electrode distance dh can be defined as the sum of the photoluminescent signal measured on the surface of interest which corresponds to the surface equal to the width of the electrodes (parallel side of the electrodes 2 to 2) multiplied by the inter-electrode distance d;.

[0089] The target value dPL c,bîe can be calculated from the value of ND, the constant K, and the target value A pcMe. In this case, the value of ND can be obtained by a 4-point or TLM measurement in the dark. The value of K can be determined by calibrating the measurement system using photoluminescence for each type of photovoltaic sample (the constant K depends on the light transmission to the absorber material).

[0090] After calculating or choosing the target value dPL able, for each of the N pairs of adjacent measuring electrodes having the inter-electrode distances dh with i an integer between 1 and N, a value jdpsLaolc of a luminous intensity, for the SPL spectrum illuminating the first face 106 or the second face 107 of the photovoltaic sample 100, is determined, such that a value (jPL of surface density of a photoluminescence signal emitted from the region of the photovoltaic sample 100 located between the adjacent measuring electrodes having the inter-electrode distance dh is as close as possible to the target value dPL Clble (step b) designated by reference 20 on the [Fig.2]).

[0091] In sample 100, for the same illumination, the layer resistance and the surface density of the photoluminescent signal (dPL) differ between two different pairs of adjacent measuring electrodes due to the amount of illumination, shading, and reflections of the illumination of the measuring electrode patterns, which varies with the inter-electrode distance and modifies the injection rate of photogenerated carriers as a function of this inter-electrode distance. The pairs of adjacent measuring electrodes with the closest inter-electrode distances therefore have the closest values ​​for layer resistance and surface density of the photoluminescent signal for the same illumination.

[0092] In this method, the values ​​of the electrical resistances between the electrodes of adjacent measuring electrode pairs, denoted Rpair(dd for a pair of electrodes of Adjacent inter-electrode distances, d, are measured using SMU (source and measurement unit) type electrical measuring equipment, advantageously by a 4-wire (4W) method. In [Fig. 1], the arrows designated by reference 124 symbolically represent the measuring probes applied to the electrodes when the resistances of the different electrode pairs are measured by a 4-wire (4W) method.

[0093] Determining the values ​​rdPLc!t,ic for which the values ​​of d?L are closest to dPL ahle allows the illumination of the sample with the light intensities rdsLcM, for each of the N pairs of adjacent measuring electrodes to be applied, leading to obtaining a value of surface density of photoluminescence signal of the absorbing material layer that is as close as possible to dPLc,ble- These light intensity values ​​can be obtained by different methods, for example by successive trials or by scanning the different possible values ​​of the illumination (advantageously a scanning with the finest possible step for greater accuracy).

[0094] Another method for determining the set of light intensity values ​​jdPLcMe for which the dPL values ​​are closest to the target dPL is to perform a mapping, using the SPL spectrum but under Icarto intensity illumination, of the surface photoluminescence density (PL image) of sample 100. These measurements allow us to obtain the surface densities of the photoluminescence signal dPL(lcar / ^) between the different pairs of measuring electrodes for the Icarto light intensity. It is then possible to calculate the different jdPLcMe values ​​for which the dPP values ​​are closest to the target dPL using the following formula: _d^ Icarte

[0095] Then, during a step c) designated by reference numeral 30 in Figure 2, for each of the N pairs of adjacent measuring electrodes, with inter-electrode distance d, electrical resistance lair i\]PL target between adjacent measuring electrodes The inter-electrode distance dt is measured during illumination of the photovoltaic sample 100 with the SPL spectrum applied at the target light intensity L d' ■

[0096] During a step d) designated by reference numeral 40 in Figure 2, the value of Rsh of the layer resistance of the absorber material layer and the Rc value of the re contact resistance of the electrodes with the absorption material layer are then determined by linear interpolation between at least two of the values ​​(d^ measured in step c). The value Rsh is calculated by determining the slope / of the line obtained by this linear interpolation and using the equation y_, and the value R,

[0097] 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. In general, the curve from which this linear interpolation is implemented can correspond to that plotted from all or part of the R^L^ie (d) values ​​measured for the adjacent measuring electrode pairs. used when sample 100 is illuminated with the different associated fdPLc,ble light intensity values ​​and the SPL spectrum.

[0098] From the determined values ​​of Rsh and R, it is possible to determine, during a step e) bearing reference 50 on [Fig.2], the specific contact resistivity Pc and the transfer length LT of the absorber material layer, which are obtained by solving the following system of equations:

[0099] = Rsh.L^

[0100] with LT corresponds to the transfer distance, in cm, and Pc corresponds to the specific contact resistivity, in Q.cm2.

[0101] As an alternative to the process described above, during the different steps, it is possible to illuminate the second face 107, opposite to the first face 106, of the photovoltaic sample 100.

[0102] In the method described above, the photoluminescence signal measurements are implemented by a photoluminescence measuring device configured to measure a photoluminescence signal emitted from the photovoltaic sample 100 and positioned on the side of one of the faces 106, 107 of the photovoltaic sample 100. When the photoluminescence measuring device is positioned on the side of the front face 106, the spacings between the measuring electrodes present on the front face 106 are clearly visible on the measured photoluminescence images.When the photoluminescence measurement device is positioned on the rear face 107, the spacing between the measurement electrodes present on the front face 106 is almost not visible on the measured photoluminescence images and it is therefore necessary to locate and take into account these electrodes when processing the images obtained to calculate the surface density of photoluminescent signal d^L.

[0103] Regardless of the embodiment or variant envisaged, the illumination of The photovoltaic sample can be prepared on either the first face 106 or the second face 107 of the sample. Similarly, photoluminescence signal measurements can be performed from either the first face 106 or the second face 107 of the sample (regardless of which face is illuminated). However, if photoluminescence measurements are performed in step a), then the face from which the measurements are taken remains unchanged for steps a) and b). The illuminated face remains unchanged during steps b) and c) of the characterization process.

[0104] Fig. 3 schematically represents a characterization device 200 of a photovoltaic sample 100 used to implement the characterization process described above.

[0105] The device 200 includes a measuring device 202 IV under illumination allowing the various resistance measurements of the measuring electrode pairs described above to be carried out, for example a source and measuring unit SMU.

[0106] The device 200 also includes a variable intensity illumination device 203 corresponding for example to a solar simulator.

[0107] The device 200 also includes a photoluminescence signal measuring device 205 configured to measure the photoluminescence signals emitted by the photovoltaic sample 100 when it is illuminated.

[0108] Advantageously, the device 200 also includes a second variable intensity illumination device 206, separate from the variable intensity illumination device 203 and intended to illuminate the photovoltaic sample 100 with a light source adapted to maximize the photoluminescence signals that will be emitted by the photovoltaic sample 100 when illuminated, for example a laser source configured to emit light whose wavelength maximizes the photoluminescence phenomenon of the photovoltaic sample 100.

[0109] The device 200 also includes a computing unit 204, for example a computer, for processing the various measurement results and performing the calculations of the characterization process described above. This computing unit 204 can also be used to control the illumination devices 203, 206.

Claims

Demands

1. A method for electrically characterizing 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 dimensions 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 dr dN, with N an integer greater than or equal to 2, 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 surface density of a photoluminescence signal intended to be emitted from regions of the photovoltaic sample (100) located between the measuring electrodes of each of the N pairs of adjacent measuring electrodes (108.1 - 108.4); b) for each of the N pairs of adjacent measuring electrodes (108.1 -108.4), with inter-electrode distances dh with i an integer between 1 and N, determination (20) of a value of an intensity luminous, for a given SPL spectrum illuminating a face, corresponding to the first face (106) of the photovoltaic sample (100) or to a second face (107), opposite to the first face, of the photovoltaic sample (100), such that a value d^L of surface density of a photoluminescence signal emitted from the region of the photovoltaic sample (100) located between the adjacent measuring electrodes having the inter-electrode distance di, is as close as possible to the target value d?L cMe; c) for each of the N pairs of adjacent measuring electrodes (108.1 -108.4), with inter-electrode distance di, measurement (30) of an electrical resistance cntrc 'cs adjacent measuring electrodes presenting the inter-electrode distance dh during an illumination of said face of the photovoltaic sample (100) with the SPL spectrum applied with the light intensity jdPLable; 1 i d) determination (40) of a layer resistance value Rsh of the absorber material layer (112) and of a resistance value Rc of contact of one of the measuring electrodes with the absorbing material layer (112), by linear interpolation between at least two of the values ​​measured in step c).

2. Method according to claim 1, wherein the target value cMe is calculated from a target value of layer resistance of the absorber material layer (112) or from a target value A pcMe cpun charge carrier injection rate in the absorber material layer (112).

3. Method according to claim 2, wherein the value is calculated by TLM method by illuminating said first face (106) of the photovoltaic sample (100) with light whose spectral characteristics and intensity are predetermined, or wherein the value R^le is predefined.

4. A method according to claim 2, wherein the value R^le is obtained by calculation from the target value A p^6-

5. A method according to claim 1, wherein the target value cMe is defined from a photoluminescence measurement of a value dsL by illuminating the photovoltaic sample (100) with light whose spectral characteristics and intensity are predetermined; the illumination of the photovoltaic sample and the photoluminescence measurement are carried out on said first face.

6. Method according to claim 1, wherein the target value cMe is predefined.

7. A method according to any one of the preceding claims, wherein step b) is carried out: - by mapping, with the SPL spectrum and under an illumination intensity Imap, the surface density of the photoluminescence signal dL( / map) of the photovoltaic sample (100) between each of the A pairs of adjacent measuring electrodes (108.1 - 108.4), and by calculating the different values ​​of jdPL,cMe allowing the same value cMe to be obtained between each pair of electrodes such that ^map fch OR - by successive trials or with a sweep of different possible values ​​of jdPL,Me.

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

9. A method according to any one of the preceding claims, wherein the absorber material layer (112) comprises a crystalline semiconductor layer, the layer stack further comprising at least two amorphous semiconductor layers (114, 116, 118, 126) between which the absorber material layer (112) is disposed.

10. A method according to any one of the preceding claims, wherein each of the measuring electrodes comprises a portion of metal (122) disposed on a portion of conductive transparent oxide (120).

11. 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 dimensions 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, with N an integer greater than or equal to 2, 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.