WO2010106534A1

WO2010106534A1 - Measurement of thin film photovoltaic solar panels

Info

Publication number: WO2010106534A1
Application number: PCT/IL2010/000175
Authority: WO
Inventors: David Scheiner; Nathan Persky; Benjamin Shoham
Original assignee: Brightview Systems Ltd.
Priority date: 2009-03-16
Filing date: 2010-03-03
Publication date: 2010-09-23
Also published as: TW201105949A

Abstract

A method for measuring characteristics of a stack of thin films including at least one thin film being an absorbing film. The measurement takes place in determined measurement locations utilizing existing and specially introduced photovoltaic panel features.

Description

MEASUREMENT OF THIN FILM PHOTOVOLTAIC SOLAR PANELS

TECHNOLOGY FIELD

[001 ] The method and apparatus relate to the field of photovoltaic thin film characteristics measurement and in particular to the measurement of parameters of photovoltaic thin film stacks including an absorbing thin film.

BACKGROUND

[002] Photovoltaic panels are an environmentally friendly source of electrical energy operated by absorbing incident solar radiation and converting it into photo-current. Thin film photovoltaic (PV) panels represent a plurality of thin films (TF) deposited on top of each other on a flexible or rigid substrate. Some of the thin films are contacts enabling collection of electric current produce by a thin film possessing photovoltaic properties. The TF PV panel produces the current by absorbing the incident solar radiation in a certain layer or layers and converting it into photo-current. The thin film layers with photovoltaic properties are also termed as absorbing films or layers. Some of the thin films forming the contacts are transparent and some are opaque or at least partially opaque.

[003] In order to provide high solar-energy to photo-current conversion efficiency and long-term stability, the optical absorption of the absorbing film should be optimized across the spectrum of the solar radiation or illumination.

[004] One of the optimization methods includes proper engineering of the Energy Gap (EG) of the absorbing film to approximately coincide with the long wavelength edge of the solar spectrum. (In this disclosure we also use the term Energy Gap for instances where the term optical band-gap, band-edge or absorption edge is sometimes used in the literature.) This is relevant for most PV materials including amorphous Silicon, micro-crystalline Silicon and cadmium telluride (CdTe) and ternary and quaternary materials such as copper indium di-selenide (CIS) and copper indium gallium di-selenide (CIGS), as well as others. The material characteristics to be controlled that can affect the EG include: stochiometry, crystal phase, level of crystal Unity, doping concentration, concentration of impurities, concentration of traps, grain-size, grain crystal orientation, grain shape, grain boundary passivation, void density and others.

[005] Spectral measurements such as reflectivity, transmission and spectral ellipsometry may be used to characterize such absorbing films. Optical models of thin films and thin film stacks may be used to provide corresponding theoretical spectra which could be fitted to the measured spectra. Optical models can be based on calculation of light propagation through the stack of materials where the layers can be defined by parameters such as thickness, refractive index and extinction coefficient as well as the effects of interfaces, scattering, spatial gradients in material characteristics and others.

[006] A fitting procedure is usually carried out whereby the parameters of the optical model are varied until a high level of correspondence or matching is achieved between the theoretical spectra and the actually measured spectra. The theoretical spectra characteristics correspond to the characteristics of the thin film actually measured.

[007] Reliable spectral measurements require a certain magnitude of reflected or transmitted illumination, which is not always available when the stack includes one or more absorbing or opaque films.

[008] There is a recognized need for a method of reliable measurement of characteristics of thin film stacks including at least one absorbing or partially opaque film.

BRIEF SUMMARY

[009] A method for measuring characteristics of absorbing layers of thin-film photovoltaic panels, where the panel includes a stack of thin films with at least one thin film being an absorbing film. A broadband illumination illuminates the stack in locations where measurement of characteristics takes place. A spectrometer with a built-in detector measures and determines the spectra of reflected or transmitted illumination. Thin film parameters are defined by correlation of the measured thin film spectra with thin film parameters corresponding to an optical model of the stack and a dielectric function model of the stack. [0010] Based on spectral measurements, a dielectric function model of at least some of the layers of the stack may be established and used in the production process control. The determined stack parameters may include the thin film characteristics such as energy gap, energy gap gradient, crystal unity, crystallinity gradient, the absorption of the absorbing film and the absorption gradient. The spectra measurements may be performed on a photovoltaic panel in a cell area, a scribe line area, and specially formed target openings formed in at least one layer of the thin film stack.

BRIEF DESCRIPTION OF THE DRAWINGS [001 1 ] In order to understand the apparatus and the method and to see how it may be carried out in practice, a number of exemplary embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0012] FIG. 1 is a schematic illustration of a typical thin film stack. [0013] FIG. 2 A is a schematic illustration of a typical thin film photo voltaic panel structure. [0014] FIGS. 2 B - 2C are enlarged sections providing additional details of the typical thin film photo voltaic panel structure of FIG 2. [0015] FIGS, 3A and 3B are schematic illustrations of an exemplary embodiment of a location suitable for measurement of parameters of an absorbing thin film deposited on top of a contact layer over a scribe line. [0016] FIGS. 4A and 4B are schematic illustrations of another exemplary embodiment of locations suitable for measurement of parameters of an absorbing thin film deposited in a measurement target area. [0017] FIG. 5 is a schematic illustration of an exemplary scribe line made in a deposited layer. [0018] FIGS. 6A and 6B are schematic illustrations of an exemplary embodiment of the present measurement method for measurement of thin film parameters with a large illumination spot. -A-

[0019J FIG. 7 is a schematic illustration of an exemplary embodiment of the present measurement method utilizing a single wide area illumination system. [0020] FIG. 8 is a magnification of FIG 2B and is a schematic illustration of a scribe lines zone. [0021 ] FIG. 9 is a schematic illustration of a typical thin film manufacturing line equipped with the present system for measurement of thin film photo voltaic panel. [0022] FIG. 10 is a flowchart illustrating an exemplary process of thin film photo voltaic panel parameter measurement process by the present system. [0023] FIGS. 1 IA -1 1 C are exemplary illustrations of transmission and reflectivity of a CIGS absorbing layer.

BRIEF DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0024] FIG. 1 is a schematic illustration of a typical thin film stack. Such stacks are produced for different applications employing thin films and in particular in photovoltaic panels. The panel 100 includes a conductive film 104, e.g. metal or TCO (Transparent Conductive Oxide) deposited upon a transparent or opaque substrate 108 and coated by an absorbing or partially opaque film 1 12. In photovoltaic panels the absorbing thin film 1 12 would typically be a semiconductor material like silicon (Si). cadmium telluride (CdTe), copper indium gallium di-selenide (CIGS) or similar. Another conductive (TCO or opaque metal) film 1 16 covers the absorbing film 1 12. At least one of layers 104 and 1 16 is transparent. This typical photovoltaic thin film structure is used in solar panel production. The absorbing film I 12 contains p-n junctions and films 104 and 1 16 serve as conductive contacts to these junctions.

[0025] A typical thin-film solar panel structure is illustrated in FIGS. 2A - 2C. Panel 200 is usually cut by scribe line zones 202 into multiple strips 208, called cells, which are connected in series, thereby providing a combined high voltage output. This method of connecting cells in series is often called monolithic integration. The cells are usually formed by scribing, i.e. removing a narrow strip, of the material at least through some of the layers at a number, usually three, of stations in the manufacturing process. FIG. 2B illustrates a scribe line zone 202, which typically would be a cluster of three scribe lines 204 usually marked Pl , P2, and P3. FIG. 2C illustrates a cross- section of a typical scribe line zone after completion of the three scribe lines showing the cuts in the contact layer 104, absorbing layer 1 12, and contact layer 1 16 such that they enable series connection of individual cells.

[0026J Spectral measurements such as reflectivity, transmission, and spectral ellipsometry may be used to characterize the absorbing films. Such spectral measurement can be implemented as part of a scheme to control the material deposition conditions in order to maintain high quantum conversion efficiency. The deposition process parameters controlled can be at least some of the following: source materials flow rate, source materials flow ratio, ambient temperature, ambient pressure, substrate temperature, substrate motion speed, process time and others. In multiple step processes the above parameters, as well as relationships between parameters of the different steps, can be controlled. For example, in one type of CIGS multi-step deposition process where a ternary CIG (Copper Indium Gallium) material is converted into quaternary material (CIGS) by adding a fourth component by diffusion (Selenium), the relation of the deposition step time to the diffusion step time and temperature requires control.

[0027] Based on spectral measurements, a dielectric function model of at least some of the layers of the stack may be established and used in the production process control. The dielectric function model can be based on a number of known models such as Lorentz oscillator, Tauc, Drude, effective-medium approximation, Cauchy and others or combinations thereof.

[0028] Such dielectric function dispersion models can be developed to accurately fit the reflectivity, transmission and spectral ellipsometer signal of layers over a wide wavelength range. For layers whereby part of the spectrum is completely absorbed in the material it is not possible to directly measure the full spectral range of dielectric function. This is the situation with a number of solar panel types since the layers are designed to essentially absorb the wavelength range of terrestrial solar radiation.

[0029] The following describes methods enabling characterization of the dielectric function in the absorbing wavelength range during manufacturing of solar panels. A set of solar panel samples of nominal thickness is prepared with the full range of expected process variations. Variations can be in at least some of the following parameters: source materials flow rate, source materials flow ratio, ambient temperature, ambient pressure, substrate temperature, substrate motion speed, process time and others. When the material can be deposited at lower thickness than the nominal thickness used in manufacturing of the solar panels without significantly affecting the material characteristics, a second set of thin, essentially transparent, samples can be prepared. This set, which is at least partially transparent throughout the required wavelength range, is used to obtain a more accurate model of the dielectric function throughout the range. The second set can be prepared by deposition at reduced thickness and/or controlled removal of material by a process such as etching or chemical mechanical polishing (CMP). In the calibration process spectral measurements are carried out, fitting of optical models is performed and the dielectric functions for all samples is calculated. By matching the dielectric function of corresponding samples from the two sets, the applicability of the dielectric function for the full range of process variations may be verified. The dielectric function models are thus calibrated to enable control of material characteristics in the fully absorptive wavelength range during manufacturing by fitting the dielectric function in the non- absorptive wavelength range and performing extrapolation of the dielectric function into the absorptive wavelength range. 0] In cases where material characteristics are thickness dependent, a second thinner set of essentially transparent material is prepared in addition to the nominal thickness set,. Both sets are characterized throughout their range of transparency. In the calibration process spectral measurements are carried out, fitting of optical models is performed and the dielectric functions for all samples is calculated. A correspondence table or correspondence function is prepared, associating samples of the thick set with the closest sample or samples of the thin set, based on the dielectric function in the overlapping non-absorptive range. If required, additional thin samples can be prepared with additional process variation to widen the coverage, or alternatively provide interpolation, and enable essentially full extension of the dielectric function of the nominal set into the absorptive wavelength range. The dielectric function models are thus calibrated to enable control of material characteristics in the fully absorptive wavelength range during manufacturing by fitting the dielectric function in the non-absorptive wavelength range and performing extrapolation of the dielectric function into the absorptive wavelength range.

[0031] Due to the importance of controlling the quantum efficiency (QE) in solar panel manufacturing, a technique to obtain the relation between the spectral dependence of the QE and the spectral dependence of the absorption of the absorber layer may be employed, in addition to the dielectric function calibration previously described. This can be utilized in production to provide information on the expected end-of-line QE based on optical measurements performed after the deposition of the absorber layer, i.e. numerous process steps prior to formation of a complete electrically testable solar panel.

[0032] A correlation exists between the spectral dependence of the absorption of the absorber layer and the spectral dependence of the quantum efficiency (QE) of the completed solar panel. The factors that possibly reduce this correlation can include: absorption in other layers, light scatter, recombination of photo-generated carriers and others. Certain areas of the absorption spectrum have a higher correlation to the QE. for example near the wavelength associated with the EG. The reduction in correlation is also affected by changes in the absorber layer due to process variation. Changes in the absorber layer across the full range of process variation can induce changes in the correlation through a number of effects, for example: different effects of subsequent thermal budget, changes in energy band offsets, interface state density changes, changes in inter-diffusion of layers and others.

[0033] A set of solar panel samples is prepared with the full range of expected process variations. Thereafter, the samples (or an equivalent set) are used to form finished and operating solar cells and the spectral dependence of the QE is characterized. The dielectric function is characterized for each sample and, if required, extrapolated into the absorptive wavelength range, as described previously, and the corresponding spectral absorption dependence obtained. A wavelength dependent relation is found for each sample by calculating the ratio of the QE to the absorption of the absorbing layer. The wavelength dependent ratio of the QE to absorption is thus obtained for the range of expected process conditions. Thus changes in the process can be controlled with the QE as the target to be optimized. [0034] In order to maximize the amount of independent spectral information, and thereby enhance the accuracy of the dielectric function modeling, a large amount of independent spectral measurements at different measurement conditions is preferably made. These include such measurements as normal incidence transmission and reflectivity, oblique incidence transmission and reflectivity, and/or spectral ellipsometry. Measurements with variable collection angles, variable numerical apertures, and Fourier plane spatial filters can also be used, including wide angle collection with integrating spheres. In addition to this the broadband illumination may be selected to include at least one of illumination ranges or optical radiation ranges of for example, UV illumination, visible illumination, and IR illumination.

[0035] Performing all of these measurements within the manufacturing process flow is difficult because many TF PV manufacturing processes utilize opaque substrates or are performed with an initial coating of opaque conducting material over the supporting transparent substrate.

[0036] Information from multiple measurement channels obtained through the different measurements, attributed to the same location may be obtained by making measurements in nearby locations of maximum predefined separation. Due to the typically large variation length scales of the TF PV processes, this can be a separation of the order often millimeters, i.e. on the scale of a cell width. Thus different types of measurements can be carried out with different optical systems and the measurements subsequently combined for analysis.

[0037] In processes with an initial thin film coating of opaque conductor over the supporting transparent substrate, reliable transmission measurements of the absorber layer deposited on the opaque layer may be performed by forming an area devoid of the opaque material. In one exemplary embodiment, this can be achieved without additional production processes or operation steps by measuring the thin film characteristics in the scribed lines or areas, which are formed to separate between the cells of the solar panel. FIG. 3 is a schematic illustration of an absorbing thin film 312 deposited on top of a contact layer 308 after formation of a scribe line 304 in the contact layer. This scribe line is typically called P l and in some cases the contact layer consists of opaque material. The scribe lines 304 are relatively narrow stripes where the conductor 308 is removed prior to the absorber 312 thin film deposition. Measurements can be performed directly in the scribe lines after the conductor layer is removed and the absorbing layer is deposited directly on the transparent substrate 316. For example, in a CIGS solar panel production process where a thick opaque layer of Molybdenum, acting as a conductor layer 308, is initially deposited on a glass substrate, the scribe lines remove the Molybdenum layer permitting transmission measurements of the subsequently deposited CIGS absorbing film.

[0038] A reflectivity measurement in the wavelength range from about 400nm up to at least l OOOnm is performed on the cell area where the layer stack is CIGS on Molybdenum. Additional measurement may be made on the scribe line 304 where the layer stack is CIGS on glass 316. This second measurement can be reflectivity or transmission and may be performed on measurement targets opened in the Molybdenum layer within the cell area. In an embodiment, an apparatus with optical systems located above the panel with spot size larger than the scribe line width and wavelength range of about 400nm to about 1700nm, performs separate reflectivity measurements on the cell area and on the scribe line. The scribe line signal is separated from the cell signal by the weighted method described below. The two separate cell and scribe line layer stacks are fitted by two optical models with common layers but different substrates, thereby providing enhanced information of the CIGS layer stack in the non-absorbing range above 800nm.

[0039] The method may be applied for characterizing the EG, absorption and thickness of amorphous Silicon (a-Si) during the manufacturing process where the absorber layer 330 is deposited on a transparent conductive oxide (TCO) 334 in FIG.3B and to some extent repeats the profile of the layer on which it is deposited. In many manufacturing processes TCO with a high degree of surface roughness 338 is used which also results in roughness in the subsequent layers deposited on it. The roughness causes light scattering, thereby distorting the optical signal in transmission, reflection and spectral ellipsometry measurements. This distortion inhibits the ability to correctly model and measure the optical parameters of the a-Si absorber layer. Performing measurements on the scribe line 342, where the TCO has been removed, enables a clearer and more representative signal to be obtained from the a-Si layer thereby enabling more accurate measurements of the characteristics of the layer. Similarly, implementing measurement targets in the TCO layer enables a clearer measurement.

[0040] Measurements on the scribe line with a large measurement spot are possible whereby the scribe line signal is separated from the cell signal by the weighted measurement method described below. In certain cases approximate optical models taking into account the scattering caused by the layer roughness can be used for direct measurement on the rough areas. The separation of a signal from the scribe line by the weighted measurement method enables enhancement of the measurement accuracy of the layer characterization. To characterize the a-Si absorber layer, the two separate cell and scribe line layer stacks are fitted by two optical models with common layers but different substrates and roughness effects, the additional measurement information thereby providing enhanced accuracy of the characteristics of the a-Si layer. This measurement can be performed by reflectivity, transmission or spectral cllipsometry in the wavelength range from about 400nm up to about lOOOnm. When it is possible to implement in the manufacturing process, measurement targets opened in the TCO layer in the cell area can be substituted for the scribe line measurements. The advantage of measurements directly on the scribe line is the ability to perform the characterization without the need for changes to be implemented in the manufacturing process.

[0041 ] In an additional embodiment shown in FIGS. 4A and 4B, where specific contact material removal regions (measurement targets) can be formed at predefined locations across the solar panel. The material is removed during the scribing process step, usually performed by laser, which takes place prior to absorber layer deposition. These targets are subsequently coated with absorber material, and spectral measurements including transmission can be performed.

[0042] Implementing measurement targets can be beneficial both in opaque and transparent conductive layers. TCO layers have a rough surface dispersing the incident and transmitted illumination and adversely affecting the measurement results. Measurement targets formed whereby such films are removed may alleviate the surface roughness influence and enable higher quality of measurements to be performed on layers subsequently deposited.

[0043] The area of the target 404 as compared to the area of the cell 208 is small and does not significantly affect the output of the cell. Therefore, if the area of the target 404 relative to the area of the cell 208 is small, at a level less than the statistical variation of the photocurrent of various cells in the solar panel, the degradation of the solar panel energy efficiency will be negligible. The shape of the targets 404 can be, for example, a square island enclosed within the cell. Alternatively, it can be added as a lateral extension of the scribe line on the side of which no additional scribe lines are added at subsequent steps of the process. The size of the targets 404 may be much larger than the width of the scribe lines 204, thus relaxing the requirements for spot- size and alignment of the optical system.

[0044] In some cases where the manufacturing process does not allow implementation of such measurement targets, for example if a needle-based mechanical scriber is used, the transmission measurements can be performed in the scribe lines. In order to alleviate the influence of possible roughness of the edges and floor of the scribe lines, the transmission signal may be measured and averaged in a number of locations along the line. Alternatively, the measurements may be performed over the scribe line area with a large illumination spot whereby a transmission signal is collected.

[0045] FIG 5 which is a schematic illustration of an exemplary scribe line made in a layer 508. If the floor 500 of the scribe line 504 is not flat, as illustrated in FIG 5, for example due to the concave indentations 512 in the substrate 516 caused by the pulsed laser scribing, the spectral characteristics along the scribe line 508 could vary considerably. Generally, the characteristics along the scribe line may vary with each step 520 of the scribing laser and the variations may be both along and across the scribe line (both the width and the thickness of the scribe line). If the thickness variation of a thin layer located in the scribe line is of the order of more than tens of nanometers, the spectra from high and low regions could possess considerable differences in location of maxima, whether measured by reflection, transmission or other type of spectral signal. Measurement with a spot size large enough to contain areas of such varying thickness could lead to weakening or even cancellation of the expected spectral oscillations in the measurement signal due to averaging of the signals from the different regions.

[0046] Use of a small spot size can enable local sampling of varying thickness regions. Due to the continuous motion of the panel in relation to the optical system, a very short measurement sampling time is required to limit the above averaging effect. The measurement can be performed with multiple short measurements, possibly with strobe-illumination, which are subsequently separated into groups of similar characteristics. The signal to noise of the signal can be improved by averaging within each group. The spot size required to perform this method is of the order of the scribe line width or less. The signals could be grouped such as to provide information on maximum and minimum thickness within the scribe line or alternatively if the spot size is sufficiently small, semi-continuous information on the profile of the floor of the scribe line.

[0047] Typically the scribe line width is between 25 and 50 microns and therefore a spot size of 10 to 20 microns may be suitable for measurements within the scribe line. If a Xenon flash lamp is used (for example Hamamatsu L9455 series) with repetition rate set at 100Hz and effective pulse length of 1 microsecond, and the solar panel travels at a velocity of 3 meters per minute, then the smearing of the spot-size due to the relative motion will be a negligible 50 nanometers and the spacing between measurements along the scribe line may be 500 microns.

[0048] Alternatively, an optional motion system can be implemented to compensate for the relative movement of the sample in relation to the optical system. The optical system can be placed on a motion system or any known in the art optical scanning methods may be employed that would scan in the direction matching the motion of the panel, "freezing" the image and thereby enabling effectively static measurement at any predetermined location. The range of motion is defined by the measurement time requirements. Based on the above example, a scanning range of 0.5 mm would be required for a 10 millisecond measurement time.

[0049] FIG 6A is a schematic illustration of an exemplary embodiment of the present measurement method for measurement of thin film parameters with a large illumination spot 604. In this embodiment, the received or detected signal intensity is enhanced by specific shaping of the illumination spot 604 into a long strip aligned in a direction parallel to the scribe line 204 (FIG 2). The illumination spot is configured to have a relatively large overlap with the scribe line and increase the transmitted signal. This strip shaped illumination spot can also be used for measuring the cell area for both transmission and reflection measurements. In order to simplify the optical system and eliminate the requirement for active adjustment of the lateral placement of the measurement location, the spot 604 width may be defined to be a certain multiple of the scribe line 204 width, depending on the lateral alignment variation of the scribe line location. The lateral alignment variation is affected by the variation of the location of the scribe line 204 in relation to the edge of the solar panel and the variation in the lateral placement of the solar panel in relation to the optical system. If this variation is large in relation to the spot width, then the optical system may be required to perform lateral alignment of the spot location relative to the solar panel prior to the measurement in order provide proper overlap of the spot with the scribe line. To improve the quality of signal measured from the scribe line, when the signal from the cell area is not negligible, an additional measurement can be carried out within the cell area only. After correctly weighting the cell measurement by the cell to scribe area ratios within the spot size, it can be subtracted from the scribe line measurement and the signal is renormalized in order to obtain a pure scribe line signal. In case of transmission measurements, this is useful if the cell area is at least partially transmitting. With reflection measurements this technique is useful in most cases.

[0050] In an alternative exemplary embodiment (F1G-6B) a large illumination spot 608 could be used, with dimension of at least the width of a cell, whereby the collecting optics for the transmitted light could collect from a large area of at least one cell width thus enabling transmission measurements through at least two scribe lines. Use of a larger spot size enables simplification of the optical system and reduces the need for active lateral motion of the measurement location. f 0051 ] Further simplification of the optical system for transmission measurements can be achieved by implementing a single wide area illumination (FIG 7) system 702 which illuminates a strip along the whole width of the solar panel 704 while a series of collecting optics systems 708 is located on the opposite side of the panel where each col lector receives its signal from a small number of scribe lines. It is also possible to use a smaller number of collecting optics systems and scan them along the illuminated area while performing measurements.

[0052] FlG 8 is a magnification of FIG 2B and is a schematic illustration of a scribe lines zone showing measurements at different locations and the weighted contributions of the various features to the measured signal to enable a weighted measurement method to separate the contributions of the features, where the term features can include at least some of cell area, Pl scribe line, P2 scribe line and P3 scribe line. Measurements are carried out at later stages of the manufacturing process after formation of two or more scribe lines in the scribe line zone, for example P l for isolation of contact layer 104 and P2 for separation of absorption layer 1 12 regions. In order to separate the signal of the scribe lines from the signal of the cell and also separate between the scribe line signals, it is necessary to perform at least two measurements and often even more than two. If the transition of the edge of the spot size is well defined and smaller than the distance between the different scribe lines within a single scribe line zone, multiple measurements are carried out on the cell (SO), on cell and first scribe line P l (measurement signal S0*(1 -a)+S l *a). and on the cell both first Pl and second P2 scribe lines (measurement signal S0*(l -b- c)+S l *b+S2*c), where SO, S l , and S2 are the pure measurement signals of the cell. Pl , and P2 areas respectively, and a, b or c are coefficients determining relative contribution of each area to the signal.

[0053] Coefficients a, b, and c can vary by wavelength depending on the variation of measurement spot size by wavelength. Additional measurements can be carried out to capture different ratios of signals from the different features. If the signal contributed by the cell area to the measured spectrum is negligible, for example due to strong scatter caused by a rough surface or in a transmission measurement where the cell area is highly absorbing, then only the latter scribe line measurements are required. If the intensity transition at the edge of the spot is not sharp, i.e. longer than the distance between the scribe lines, then a series of measurements is required with a controlled movement between them perpendicular to the scribe lines. [0054J The series of measurements should include at least a cell only measurement (measurement signal SO), a measurement with partial contribution from first scribe line (measurement signal S0*(l-a)+Sl *a), a measurement with partial contribution from first scribe line and partial contribution from second scribe line (measurement signal S0*(l-b-c)+S l *b+S2*c). Additional measurements can be carried out to capture different ratios of signals from the different features. Based on data of the relative lateral position of the measurement points, the measurements can be fitted to a function of the lateral spot intensity distribution convoluted with the contribution of the two scribe lines as illustrated in FIG 8. This can be carried out separately for each wavelength of the spectrum if the spot profile is different for different wavelengths. The spot lateral spectral intensity distribution can be found separately by various means, such as scanning over a knife-edge or knife-edge mirror or narrow slit.

[0055] Following the fitting of the scribe line contributions to the convolution signal, these contributions can be separated and analyzed for their respective spectral characteristics in order to fit the optical model and calculate the parameters of the respective layer stacks in each scribe line. This method can be carried out using reflection, transmission or spectral ellipsometry measurements and combinations thereof.

[0056] Transmission measurements can also be carried out in the scribe line during relative motion between the optical system and the solar panel. In one embodiment, where the panel is located on a continuously moving conveyer, the optical system is aligned over the scribe line and the panel travels in a direction essentially parallel to the scribe line. In this way, the measurement time can be extended, thereby improving the signal to noise ratio and smoothing out effects of possible local roughness in the scribe line. The optical system can be pre-aligned in the manufacturing line to overlap a specific scribe line. Multiple optical systems can be placed to simultaneously sample multiple scribe lines across the width of the panel in order to provide mapping capability and enable control of the lateral uniformity of the manufacturing process. In another embodiment, a single optical system can be aligned to measure on a single scribe line, and shifted in steps which are a multiple of the cell width, thereby sequentially sampling multiple scribe lines across the width of the panel to provide scribe line mapping capability. In certain conditions, where rotation of the solar panel in relation to the direction of movement is large, a system of active lateral alignment of the measurement spot location could be required to maintain proper overlap of the measurement spot with the scribe line. If multiple optical systems are used, they could be moved simultaneously to follow the scribe lines and maintain proper overlap of the measurement spot. The multiple optical systems could be attached to a common mechanical interface allowing a single motion mechanism to be used.

[0057] In thin film photovoltaic panel production processes where the thin films are deposited on opaque substrates, transmission measurements cannot be performed. Enhanced information can be obtained in this case by measuring reflectivity and/or spectral ellipsometry at different incidence angles. It is also possible to add information on the layer by performing separate reflectivity measurements of the absorber layer within the cell area as well as in the scribe lines. This provides two independent sets of measurements on layer stacks with effectively different substrates. Measurement targets, as described previously, can be implemented during the scribing step, thus enabling relaxed requirements of illumination spot-size and alignment for the measurement on the scribe line layer stack.

[0058] FIG. 9 is a schematic illustration of a typical thin film manufacturing line equipped with the present system for measurement of thin film photo voltaic panel parameters. Each layer is deposited at an appropriate deposition workstation and a conveyor 900 advances the panel 200 (FIG. 2) between the stations. Following deposition of the absorber layer a solar panel 200 usually advances along a conveyor system 900 and passes through an apparatus 904 consisting of multiple optical systems exemplified by 916 and 920. The optical systems may be located above the panel, below the panel, and both above and below the panel. The optical systems are pre-aligned so as to be located above and/or below specific areas of the moving panel 900. At least some of the optical systems, for example systems 916, can be located whereby they measure in the cell 208 area, some systems, for example systems 920. can be located on the scribe lines and some can be located to enable measurement on measurement targets 404 (FIG. 4). An optional position control module or modules 908 can be operative to provide lateral and longitudinal positioning movement as indicated by arrows 910 and 912 to compensate for the location of the optical systems in relation to the location of the panel 900 and the scribe lines 204. Position control module 908 may be further operative to provide rotation and compensate for the location of the optical systems in relation to the location of the panel 900 and the scribe lines 204. The positioning module can rotate the whole apparatus 904 or rotate each of the optical systems 916 and 920 separately. One or more detectors 928 sense orientation of the panel 900 with respect to optical systems 916 and 920 orientation. A controller 932 controls and synchronizes operation of all units of the system. 9] FIG. 10 is a flowchart illustrating an exemplary process of thin film photo voltaic panel parameter measurement process by the present system. Upon receiving an input-signal that a panel is approaching (Block 1000), the apparatus initiates a measurement sequence. The signal for panel arrival is received from the conveyer system 900 or is generated by a specific detector 928 placed upstream of the optical systems. The detector 928 senses orientation of the panel 900 (Block 1004), and the lateral offset and angle of the scribe line 204 (Block 1008), in relation to a nominal position and nominal angle. The information is sent to the system controller which calculates corrective motion and sends a correction signal to a positioning module that controls the lateral position of the multiple optical systems. The positioning module corrects the lateral location of the multiple optical systems (Block 1012), so that the optical systems pre-determined to measure on specific features such as scribe lines, cells or measurement targets are well aligned to the respective features and, if needed, continuously offset to follow the possible diagonal movement of the features. Controller 932 synchronizes the measurements of the different optical systems 916 and 920 based on a predefined measurement plan (Block 1016). Optionally, the detector 928 can also be positioned so as to be able to detect the presence and longitudinal location of a measurement target 404 on the moving panel thereafter a signal is sent to the controller 932 in addition to the panel orientation information. The controller calculates the required timing for measurement on the easurement targets and thereafter the required optical systems are appropriately activated to perform synchronized measurements on the targets (included in Block 1016). [0060] Measurements are repeated at multiple positions along the length of the panel in order to generate a map of the panel characteristics. Data from all measurement channels is received by the controller (Block 1020) and transferred to a data system. Measurements from multiple locations within a predefined distance, usually similar to a cell width, are combined into an extended data set. The extended data set is analyzed by comparing each measurement of the set to an appropriate optical model. Each optical model consists of at least one thin film or thin film layer stack which is used to calculate a corresponding theoretical spectrum fitted to a measured spectrum. Optical models are based on calculation of light propagation through the stack of materials where the layers are defined by parameters such as thickness, refractive index and extinction coefficient as well as the effects of interfaces, scattering, spatial gradients in material characteristics and others.

[0061] A fitting procedure is carried out whereby the parameters of the optical model are varied until a high level of correspondence or matching is achieved between the theoretical spectra and the actually measured spectra. The theoretical spectra characteristics correspond to those of the thin film actually measured.

[0062] The information determined on the thin film characteristics of at least the absorber layer may be communicated to upstream and downstream located production equipment and wherein the communicated parameters enable absorbing layer formation process control. The process parameters controlled can be at least some of the following: source materials flow rate, source materials flow ratio, ambient temperature, ambient pressure, substrate temperature, substrate motion speed, process time and others.

[0063] To facilitate measurement of layers and layer stacks with multiple varying parameters, as much independent information as possible needs to be collected. Expanding the wavelength range of collected light improves the ability to separate effects of different parameter changes in the layers. Combining at least two of the three wavelength ranges of ultra-violet, visible and infra-red facilitates such an enhancement. For example combining spectral sensors of VIS-NlR (400nm-1000nm) and IR (950nm- 1700nm) creates an optical system that covers the operating range of the solar panels as well as the lower energy IR range where the materials become transparent.

[0064] One of the techniques used to enhance the QE of the solar panels is based on engineering of the materials by controlled variation of the depth dependency of the material characteristics. For example, the stochiometry of the materials is varied during deposition in order to form a grading of the EG, thereby improving current and voltage characteristics of the cell. In order to control such a process, the information gathered by the measurement is required to be extensive enough to enable modeling of the EG as a function of depth and not just an average value for the layer stack. In order to facilitate characterization of a multi-layer or graded-layer absorber stack, a single- layer stack optical model is used to fit the measured reflectivity signal in the fully absorbing wavelength range below the EG (FIG. 1 IA), usually in the range from 400nm to about 800nm or that indicated as absorption region in FIG. 1 1C, the longer wavelengths are determined by the EG of the absorbing material measured. A full layer stack optical model is used for the transition and transparent region (FIG. 1 1 B). from about 800nm, where the top layer 1 104 of the complete stack model is common with the single-layer stack and the rest of the full layer stack 1 106 is modeled as graded or step-wise. The boundary wavelength between the two wavelength regions is determined by the type of absorber material and its nominal thickness. Depending on the value of EG, the layer stack is usually transparent from about wavelength IOOOnm and up (FIG. l 1C). This separation into wavelength regions with different optical models, though with common parameters, enables a faster calculation convergence.

[0065] Transmission measurements performed on the same layer stack yield no signal in the fully absorbing wavelength range (FIG. 1 1C). The signal however, begins to increase in the transition range from about 800nm, depending on EG. In the transparent range from about I OOOnm and up, both the reflectivity and transmission spectra contain oscillations which are dependent on the thickness and dielectric function of the layers, especially of the absorbing layers. Fitting an optical model to at least two of the following four measurements, where at least one is a reflectivity measurement: reflectivity from the cell area, transmission from the cell area, reflectivity from the scribe line area and transmission from the scribe line area, enables the absorbing layers dielectric function, gradients and layer thickness to be characterized. The existence of gradients in material properties is recognizable by changes in the amplitudes of the oscillations in the transparent range. The direction of gradient in the layers can be defined by fitting at least some parameters of the dielectric function of the surface layer 1 104 as measured by reflectivity in the fully absorbing wavelength range (FIG. 1 1 C).

[0066] The above technique can be implemented when there is an additional. essentially transparent layer, on top of the absorbing layer. In this case, the additional layer is added to the top of each layer model, i.e. on top of the common layer.

[0067] A known technique to increase the efficiency of CIGS solar panels is by forming gradients in the composition of the CIGS layer thereby inducing EG gradients and formation of internal electrical fields which act to increase the quantum efficiency. The analysis using at least the cell reflectivity measurement can provide information on such EG gradients and absorption gradients. The technique described above for separating the models used in different wavelength ranges can be implemented for the CIGS process.

[0068] In order to enhance the efficiency of the solar panels by more efficient capture of the solar spectrum, tandem or multi-junction structures are fabricated with multiple absorber layers with different EG deposited in series to form a stack. The present method may also be applied for characterizing the EG, absorption, crystal unity, and thickness of the layers of tandem structures such as micro-crystalline Silicon (μc-Si) on amorphous Silicon layer where the absorber layers are deposited on a usually rough transparent conductive oxide (TCO). The μc-Si layer typically consists of varying concentration of small grains of crystalline Silicon imbedded in a-Si. The level of crystallinity is often defined in units of volume fraction. Implementing a scribe line or measurement target measurement greatly enhances the ability to separately characterize the a-Si and μc-Si layers and provide details of the crystallinity and crystallinity gradients within the μc-Si layer. A reflectivity measurement in the wavelength range from about 400nm up to about I OOOnm is performed on the cell area where the layer stack is μc-Si on a-Si on TCO. Additional measurement may be made on the scribe line area where the layer stack is u-Si on a-Si on glass. This measurement can be performed by reflectivity, transmission or spectral ellipsometry in the wavelength range from about 400nm up to about l OOOnm. When it is possible to implement in the manufacturing process, measurement targets opened in the TCO layer in the cell area can be substituted for the scribe line measurements. The advantage of measurements directly on the scribe line is the ability to perform the characterization without the need for changes to be implemented in the manufacturing process. The analysis using at least the cell reflectivity measurement can provide information on EG and EG gradients, absorption and absorption gradients and crystallinity and crystallinity gradients, of the constituent layers.

[0069] The method may also be used for characterizing the absorption and EG of CdTe within the manufacturing process where the absorber layer is deposited on a CdS layer.

[0070] Incorporation of sodium into the polycrystalline structure of CIGS material has been found to be a critical factor in providing high photo-conversion efficiency. The Na atoms undergo diffusion in the material and passivate the surface states at the grain boundaries. The range of required Na concentration is defined on the one hand by a minimal level in order to access all the grain boundary surface area of the material while the maximum value is at the level where adhesion of the CIGS layer starts to deteriorate. The Na concentration also has an effect on the surface morphology of the CIGS layer. The reflectivity of the CIGS layer is affected by the Na incorporation level and concentration. Therefore, in addition to the energy gap, the dielectric function model can provide information on the Na concentration, while variations of the surface roughness, which can also be modeled, provide additional information on the Na concentration.

[0071] A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the method and electrode structure. Accordingly, other embodiments are within the scope of the following claims:

Claims

What is claimed is:

1. A method for measuring characteristics of absorbing layers of thin-film photovoltaic panels, said method comprising: providing a thin film photovoltaic panel including a stack of thin films with at least one thin film being an absorbing film and determining measurement locations; providing a broadband illumination system generating an illumination beam operatively adapted to illuminate the determined measurement locations; receiving the illumination reflected or transmitted by the measurement location by a detector and determining the spectra of said illumination; employing the determined spectra in calculating a dielectric function model of at least said absorbing film by fitting the measurement results to an optical model of the stack.

2. The method according to claim 1 wherein the dielectric function model includes at least one of a group of thin film characteristics consisting of at least one of the energy gap and the absorption of said absorbing film.

3. The method according to claim 1 wherein the dielectric function model of the absorbing film is analyzed and at least one of the energy gap, crystal unity and the absorption of said absorbing layer is determined.

4. The method according to claim 1 wherein the dielectric function model of the absorbing film is analyzed and at least one of the energy gap gradient, crystallinity gradient and the absorption gradient of said absorbing layer is determined.

5. The method according to claim 1 further comprising communicating the determined thin film characteristics to upstream and downstream located production equipment and wherein the communicated parameters enable absorbing layer formation process control.

6. The method according to claim I wherein the determined measurement locations are at least one of a group consisting of a cell area, a scribe line area, and specially formed target openings formed in at least one layer of the thin film stack.

7. The method of claim 6 wherein the openings are formed by a laser scribing apparatus.

8. The method of claim 6 wherein the openings are formed in an opaque layer.

9. The method of claim 6 wherein the openings are formed in a layer with surface roughness.

10. The method according to claim 1 wherein illuminating the stack of thin films means illuminating by at least one of a group of illuminations consisting of normal incident illumination, oblique incident illumination, and spectral ellipsometry illumination.

11. The method according to claim 1 wherein the broadband illumination includes at least two of three illumination ranges of LJV illumination, visible illumination, and IR illumination.

12. The method according to claim 1 wherein receiving the reflected illumination by a detector means illumination consisting of at least one of a group of normal incident illumination, oblique incident illumination and spectral ellipsometry illumination.

13. The method according to claim 1 wherein the illumination and the detector are operatively configured for measuring spectral ellipsometry.

14. The method according to claim 1 wherein the fitting of the optical model of the stack to at least one measurement enables determination of an accurate dielectric function model of at least the absorbing film.

15. The method according to claim 1 wherein the fitting of the optical model of the stack to at least one measurement enables determination of an accurate dielectric function model of gradients in the absorbing film.

16. The method according to claim 15 wherein fitting of the optical model includes at least one of the fitted parameters consisting of the energy gap and absorption.

17. The method according to claim 16 wherein fitting of the optical model includes at least one of the fitted parameters consisting of the energy gap gradient and absorption gradient.

18. The method according to claim 1 further comprising communicating the photo voltaic panel orientation and correcting it to match at least the detector orientation.

19. An apparatus for measurement of characteristics of absorbing layers of thin-film photovoltaic panel, said apparatus comprising: one or more broadband illumination sources operatively adapted to illuminate a predetermined location on said photovoltaic panel bearing a stack of thin films with at least one film being an absorbing film; at least one detector operatively adapted to receive the radiation of the illumination reflected or transmitted by the panel; a support operatively configured to enable relative displacement between the photovoltaic panel and the at least one illumination source and at least one detector such as to enable illumination of predetermined locations and reception of the reflected or transmitted illumination; a mechanism operatively configured to determine the location of the predetermined locations on the photovoltaic panel; and a controller synchronizing the operation of the illumination sources, illumination detector, and the support movement.

20. The apparatus according to claim 19 wherein said illumination sources provide illumination being at least one of a group consisting of normally incident illumination, oblique incident illumination.

21. The apparatus.according to claim 19 wherein said illumination sources further provide spectral ellipsometry illumination.

22. The apparatus according to claim 19 wherein said illumination sources provide illumination consisting of at least two of three ranges: UV range, visible range, and IR range.

23. The apparatus according to claim 19 wherein said illumination sources form on the photovoltaic panel a large, a small, or elongated illumination spot.

24. The apparatus according to claim 19 wherein said illumination detector receives illumination reflected or transmitted by the thin film stack.

25. The apparatus according to claim 19 further comprising a mechanism for fitting an optical model to at least one measurement and calculating an accurate dielectric function model of at least the absorbing layer.

26. The apparatus according to claim 19 further comprising a mechanism for fitting an optical model to at least one measurement and calculating an accurate dielectric function model of the gradients of the absorbing layer.

27. The apparatus according to claim 26 wherein said mechanism for fitting the optical model to at least one measurement and calculating an accurate dielectric function includes parameters of at least energy gap and absorption.

28. The apparatus according to claim 26 wherein said mechanism for fitting the optical model to at least one measurement and calculating an accurate dielectric function includes parameters of at least the energy gap gradient and the absorption gradient.

29. The apparatus according to claim 21 further comprising a mechanism for orienting at least the detector to match orientation of the measurement targets.

30. The apparatus according to claim 21 wherein at least one broad band illumination source is a single wide area illumination source operatively adapted to form an illuminated line along the whole width of the panel.

31. The apparatus according to claim 30 further comprising a plurality of illumination collecting optical systems located opposite the single wide area illumination source such that each of the collection optical systems collects light transmitted through one or more scribe lines.

32. A method for measuring characteristics of absorbing layers on a rough surface of thin- film photovoltaic panels, said method comprising: providing a thin film photovoltaic panel including a stack of thin films with at least one thin film having a rough surface; generating an opening in at least the thin film layer having a rough surface; coating the panel with at least one absorbing film; illuminating the opening by a broadband illumination; receiving the illumination reflected or transmitted by the opening by a detector and determining the spectra of said illumination; employing the determined spectra in calculating a dielectric function model of at least one absorbing film of the stack by fitting the measurement results to an optical model of the stack.

33. The method according to claim 32 wherein the dielectric function model includes at least one of a group of thin film characteristics consisting of at least one of the energy gap and the absorption of said absorbing film.

34. The method according to claim 32 wherein the dielectric function model of the absorbing film is analyzed and at least one of the energy gap, crystal Unity and the absorption of said absorbing layer is determined.

35. The method according to claim 32 wherein the dielectric function model of the absorbing film is analyzed and at least one of the energy gap gradient, crystallinity gradient and the absorption gradient of said absorbing film is determined.

36. The method according to claim 32 further comprising communicating the determined thin film characteristics to upstream and downstream located production equipment and wherein the communicated parameters enable absorbing film formation process control.

37. The method according to claim 32 wherein the determined measurement locations are at least one of a group consisting of a cell area, a scribe line area, and specially formed target openings formed in at least one thin film of the thin film stack.

38. The method of claim 37 wherein the openings are formed by a laser scribing apparatus.

39. The method according to claim 32 further comprising orienting illumination sources and the detector to match the orientation of the measurement locations.

40. A method for measuring characteristics of absorbing layers of thin-film photovoltaic panels, said method comprising: providing a thin film photovoltaic panel including a stack of thin films with at least one thin film being an absorbing film and determining measurement locations; providing a broadband illumination system generating an illumination spot operatively adapted to illuminate the determined measurement locations; receiving the illumination reflected or transmitted by the measurement location by a detector generating a signal determining the spectra of said illumination; employing the determined spectra in calculating a dielectric function model of at least said absorbing film by fitting the measurement results to an optical model of the stack.

41. The method according to claim 40 further comprising enhancing the signal intensity by specific shaping of the illumination spot into a long strip overlapping a measured scribe line and aligned in a direction parallel to the scribe line.

42. The method according to claim 40 further comprising employing a illumination spot which is multiple of a scribe line width and reducing a need for active lateral motion of the measurement location.

43. The method according to claim 41 further comprising weighting the cell measurement by the cell to scribe area ratios within the spot size and obtaining the signal of the scribe line.

44. A method of controlling Quantum Efficiency (QE) of a photovoltaic panel in a photovoltaic panel production process, said method comprising: preparing a set of photovoltaic panel samples including a full range of expected process variations; characterizing dielectric function for each of the photovoltaic including extrapolating the function into absorptive wavelength range; calculating the ratio of the QE to the absorption of the absorbing layer and obtaining the corresponding spectral absorption dependence; and establishing a target quantum efficiency and selecting process parameters enabling achievement of this quantum efficiency.

45. A method for measuring characteristics of thin films of thin-film photovoltaic panels, said method comprising: providing a thin film photovoltaic panel including a stack of thin films and determining measurement locations and nearby locations with a predetermined separation; providing a broadband illumination system generating an illumination spot operatively adapted to illuminate the determined measurement locations and nearby locations with a predetermined separation; receiving the illumination reflected or transmitted by the measurement location by a detector generating a signal determining the spectra of said illumination; employing the determined spectra in calculating a dielectric function model of at least said thin film by fitting the measurement results to an optical model of the stack.

46. The method according to claim 46 wherein the photovoltaic panel further comprises a plurality of photovoltaic cells having a predetermined cell size.

47. The method according to claim 47 wherein the separation between the measurement locations is about a cell size.

48. A method for measuring characteristics of thin films of thin-film photovoltaic panels, said method comprising: utilizing for measurement purposes Standard present on the panel production features void of at least one thin film; forming special void of at least one thin layer areas such as measurement targets; and performing thin film characteristics measurement in these areas.

49. A method for measuring characteristics of absorbing layers on an opaque layer of thin- film photovoltaic panels, said method comprising: providing a thin film photovoltaic panel including a stack of thin films with at least one opaque thin film; generating an opening in at least the opaque thin film layer; coating the panel with at least one absorbing film illuminating the opening by a broadband illumination; receiving the illumination reflected or transmitted by the opening by a detector and determining the spectra of said illumination; employing the determined spectra in calculating a dielectric function model of at least one absorbing film of the stack by fitting the measurement results to an optical model of the stack.

50. The method according to claim 49 wherein the dielectric function model includes at least one of a group of thin film characteristics consisting of at least one of the energy gap and the absorption of said absorbing film repeating the rough surface.

51. The method according to claim 49 wherein the dielectric function model of the absorbing film is analyzed and at least one of the energy gap, crystallinity and the absorption of said absorbing layer is determined.

52. The method according to claim 49 wherein the dielectric function model of the absorbing film is analyzed and at least one of the energy gap gradient, crystallinity gradient and the absorption gradient of said absorbing film is determined.

53. The method according to claim 49 further comprising communicating the determined thin film characteristics to upstream and downstream located production equipment and wherein the communicated parameters enable absorbing film formation process control.

54. The method according to claim 49 wherein the determined measurement locations are at least one of a group consisting of a cell area, a scribe line area, and specially formed target openings formed in at least one thin film of the thin film stack.

55. The method of claim 54 wherein the openings are formed by a laser scribing apparatus.

56. The method according to claim 49 further comprising orienting illumination sources and the detector to match the orientation of the measurement locations.

57. The method according to claim 49 wherein transmission measured through the opening is combined with reflection measurements on the cell in calculating a dielectric function model of at least one absorbing film of the stack by fitting the measurement results to optical models of the stacks.

58. The method according to claim 49 wherein the absorbing layer is a CIGS material and the opaque layer is Molybdenum.

59. The method according to claim 57 wherein the absorbing layer is a CIGS material and the opaque layer is Molybdenum.

60. An apparatus for measurement of characteristics of absorbing layers of thin-film photovoltaic panel, said apparatus comprising: a support operatively configured to enable relative displacement between the photovoltaic panel and at least one illumination source and at least one detector such as to enable illumination of predetermined locations and reception of reflected or transmitted illumination; one or more broadband illumination sources operatively adapted to illuminate a predetermined location on said photovoltaic panel bearing a stack of thin films with at least one film being an absorbing film; at least one detector operatively adapted to receive the radiation of the illumination reflected or transmitted by the panel; a mechanism operatively configured to determine the location of the predetermined locations on the photovoltaic panel; and a controller synchronizing the operation of the illumination sources, illumination detector, and the support movement.

61. The apparatus according to claim 60 wherein said controller and mechanism are configured to continuously follow features on the panel surface.

62. The apparatus according to claim 60 wherein said controller and mechanism are configured to perform measurements on openings in at least one thin film layer.

63. The apparatus according to claim 62 wherein said openings are scribe lines.

64. The apparatus according to claim 60 wherein said controller and mechanism are configured to perform multiple measurements on the panel.

65. The apparatus according to claim 64 wherein said multiple measurements are analyzed to generate a map of the panel characteristics.

66. A method for measuring characteristics of absorbing layers of thin-film photovoltaic panels, said method comprising: preparing one or more measurement locations on a thin film photovoltaic panel including a stack of thin films with at least one thin film being an absorbing film; illuminating said locations by a broadband illumination interacting with said locations and receiving the products of the illumination-film interaction by a detector operatively configured to determine the illumination-film interaction spectra; employing the determined spectra in calculating a dielectric function model of at least said absorbing film by fitting the measurement results into an optical model of the stack and communicating the absorbing film parameters to photovoltaic panel production equipment.

67. The method according to claim 66 further comprising orientating illumination sources and the detector to match the orientation of the measurement locations.