DE102014213575B3 - Device and method for a spectrally resolved measurement of an object - Google Patents

Abstract

The invention relates to a device for a spectrally resolved measurement of an object, comprising a light source for generating a broadband output beam, an optical decomposition unit for spectrally decomposing the output beam into at least a first and a second spectral sub-beam, a light modulator unit for modulating the first and second spectral sub-beam and a optical convergence unit for merging the modulated spectral sub-beams to a measuring beam, as well as with a measuring unit for receiving measurement signals of the acted upon by the measuring beam object. The invention is characterized in that the light modulator unit is designed to modulate the first spectral sub-beam with a first modulation type and the second spectral sub-beam with a second modulation type, wherein the first and second types of modulation are different and in that the measuring unit is designed to receive first measurement signals, which coincide with the first modulation type are modulated and second measurement signals which are modulated with the second modulation type to separate.

Description

The invention relates to a device and a method for a spectrally resolved measurement of an object according to the preambles of claims 1 and 11.

For the spectrally resolved characterization of objects, in particular of photosensors or photovoltaic solar cells, typically the object is exposed to radiation of different wavelengths and a measurement is carried out separately for each wavelength.

Typical measuring methods provide for sequentially directing radiation with only one wavelength or in a narrow frequency range onto the object to be measured and performing the desired measurement. Such measuring methods have the disadvantage that a considerable total measuring time is necessary for a large number of separate wavelengths at which a measurement is to be carried out. Thus, in photovoltaic solar cells measuring methods for the determination of external quantum efficiency (EQE) are known in which the solar cell is applied temporally successive with different wavelengths typically in the range of 250 nm to 2.5 microns. However, such measurement techniques typically take at least 20 minutes total measurement time.

Out DE 699 30 411 T2 It is known, differently modulated spectral bands in a measuring beam for detecting fluorescent substances in a sample

In order to increase the quality of the measurement signal, it is known to modulate the measurement beam with a modulation frequency and to filter the measurement signal with respect to the modulation frequency in a conventional manner, for example by means of a bandpass filter or Fourier transform. Such a structure is for example in US 8,436,630 B2 described.

It is furthermore known to generate the radiation by means of a broadband light source, in particular a halogen lamp or xenon lamp, and to generate a measuring beam with the respectively desired wavelength via an optical decomposition unit such as, for example, a grating monochromator. Likewise, the use of a micromirror unit for influencing the spectrum of the measuring beam from US 8,436,630 B2 known.

To accelerate such spectrally resolved measurements is off US 8,299,416 B2 It is known to conduct light of several narrow-band light-emitting diodes with different wavelengths simultaneously onto the test object, each wavelength being modulated with a specific frequency, so that the measurement signal for each wavelength can be separated from the overall test signal via corresponding bandpass filters. As a result, a spectrally resolved measurement can thus take place at the same time, ie without a sequential, successively connected measurement of the different wavelengths, as a result of which the total measuring duration is considerably reduced.

The disadvantage here is that the emission of the LEDs with increasing wavelength is always broadband and thus the spectral resolution decreases with increasing wavelength. In addition, the efficiency of light-emitting diodes decreases in particular for wavelengths above 1000 nm, so that only a limited spectrum can be measured with this method.

The invention is therefore based on the object of improving the previously known devices and methods for the spectrally resolved measurement of an object in order to enable a spectrally resolved measurement over a larger frequency range with a reduced overall measurement duration.

This object is achieved by a device according to claim 1 and a method according to claim 11, Preferred embodiments of the device according to the invention can be found in claims 2 to 10 and the inventive method in claims 12 to 15. Hereby, the wording of all claims by reference included in the description.

The device according to the invention is preferably designed for carrying out the method according to the invention, in particular a preferred embodiment thereof. The inventive method is preferably designed for implementation by means of the device according to the invention, in particular a preferred embodiment thereof.

The device according to the invention for a spectrally resolved measurement of an object has a light source for generating a broadband output beam, and an optical decomposition unit for spectrally splitting the output beam into at least a first and a second spectral sub-beam, a light modulator unit for modulating the first and second spectral sub-beam and an optical Merging unit for merging the modulated spectral sub-beams into a measuring beam.

It is essential that the light modulator unit is designed to modulate the first spectral sub-beam with a first modulation type and the second spectral sub-beam with a second modulation type, wherein first and second Modulation type are different. The measuring unit is designed accordingly, first measuring signals which are modulated with the first modulation type and second measuring signals which are modulated with the second modulation type to separate.

The invention is based on the recognition that the combination of a broadband light source with a light modulator unit, which is used to modulate different spectral sub-beams with different modulation types, offers considerable advantages over previously known devices for the spectrally resolved measurement of objects: The use of a broadband light source enables the Measurement over a broad spectrum, since in particular per se known xenon lamps or halogen lamps can be used, which cover a considerably broader spectrum, compared with commercially available light-emitting diodes.

Furthermore, the measuring time is considerably shortened by the simultaneous application of at least two differently modulated partial spectra to previously known devices with xenon or halogen lamps.

In addition, the device according to the invention over prior art devices with tunable light sources such as tunable lasers considerably cheaper to produce.

The method according to the invention for the spectrally resolved measurement of an object comprises the following method steps:
In a method step A, a broadband output beam is generated and a spectral decomposition of the output beam into at least a first and a second spectral sub-beam. In a method step B, the modulation of the first and second spectral sub-beam by means of a light modulator unit. In a method step C, the first and second spectral sub-beams are merged to form a measuring beam. In a method step D, the object is exposed to the measuring beam, and in a method step E, a measuring signal of the object is measured.

It is essential that in method step B the first spectral part is modulated with a first modulation type and the second spectral part is modulated with a second modulation type, the first and second types of modulation being different. Furthermore, in method step E the measurement signal is processed by separating first measurement signals, which are modulated with the first modulation type, and second measurement signals, which are modulated with the second modulation type.

Preferably, the modulation is effected by a frequency modulation in that the first spectral part is modulated with a first modulation frequency and the second spectral part with a second modulation frequency, wherein the first and second modulation frequencies are different. This has the advantage that several spectral components can be modulated with frequencies of any phase.

In a further preferred embodiment, the modulation is effected by a phase modulation in that the first spectral part is modulated with a first phase change and the second spectral part with a second phase change, wherein first and second phase changes are different. This has the advantage that a plurality of spectral components with the same modulation frequency can be resolved via their phase offset. In particular, the first spectral part is preferably modulated into a first phase and the second spectral part is modulated into a second phase, wherein the first and second phases are different. The phases differ in terms of their phase orientation.

It is also within the scope of the invention to modulate both the frequency and the phase of the spectral components. This results in the advantage that despite physical limitations of the usable frequency space, such as the inertia of the object to be characterized, to enable a further modulation diversity over the phase space.

The inventive method thus has the advantages already mentioned in the device according to the invention, in particular, as by the use of a broadband output beam, which is preferably produced by a broadband light source such as in particular a xenon lamp or halogen lamp, a wide range can be covered and a simultaneous application of the object with the first and second spectral components.

Thus, even in the method according to the invention, no sequential measurement is necessary first with the first spectral component and then with the second spectral component since, despite the simultaneous measurement due to the different types of modulation, first measurement signals, which are due in particular to the first spectral component and second measurement signals, which can be separated, in particular, by application of the second spectral component.

First and second spectral sub-beams differ with respect to their spectral Composition. The spectral beams preferably have only a small wavelength range (ie only a small frequency width), in particular each partial beam preferably has a spectral half-width equal to the minimum half-width, preferably smaller than the minimum half-width of the spectral properties of the object to be examined. Corresponding half-value widths are preferably in the range 100 nm to 0.1 nm.

In order to allow as extensive a characterization as possible, the output beam is preferably decomposed into a plurality of spectral sub-beams, preferably at least ten spectral sub-beams, in particular at least 20 spectral sub-beams, particularly preferably in the range 20 to 50 spectral sub-beams, and a separation of the measurement signals for each of the spectral partial beams accordingly takes place.

Preferably, the spectral sub-beams do not overlap each other in terms of wavelengths, i. H. Each wavelength is assigned to a maximum of one spectral sub-beam. Likewise, it is within the scope of the invention that there is a slight overlap of the partial spectra of the spectral sub-beams.

The decomposition unit is used for the spectral decomposition of the output beam. It may, for example, comprise an optical prism. In particular, it is advantageous that the dismantling unit comprises an optical grating. An optical grating has the advantage that the dispersion of the spectrally dispersed light is linear. Due to this linearity, a simple mechanical adjustment of the grating over a prism, in which the dispersion is non-linear, made possible. In addition, a grating is less expensive compared to a prism.

In particular, it is advantageous for the optical grating and the light modulator unit to be configured and arranged in such a way that the output beam spectrally split by means of the optical grating meets the light modulator unit and the at least two modulated spectral sub-beams strike this grating again. This has the advantage that only one optical grating must be used.

In a further preferred embodiment, the decomposing unit has at least one first and one second optical grating which are designed and arranged cooperatively with the light modulator unit such that the output beam spectrally decomposed by the first grating meets the light modulator unit and the at least two modulated spectral partial beams impinge on the light modulator unit hit second grid.

Preferably, the decomposing unit comprises a collimator and a dispersive element to image the output beam collimated onto the dispersive element. This results in a simplified geometric structure. In particular, it is advantageous in this case that the collimator comprises a concave mirror, preferably a parabolic mirror. Such mirrors can be purchased inexpensively commercially.

As already stated above, the decomposing unit and the light modulator unit are preferably designed to cooperate such that at least ten, preferably at least 20, more preferably at least 80, in particular at least 100 spectral sub-beams can be modulated with different types of modulation. In this way, a spectrally high-resolution measurement can be made simultaneously. In particular, it is advantageous in this case that the modulation types are different in pairs.

When modulating by means of a modulation frequency, the separation of the measurement signals can be effected in a manner known per se, depending on the respective modulation frequency:
Thus, it is within the scope of the invention that the measuring unit comprises at least a first bandpass filter for the first modulation frequency. Advantageously, the measuring unit additionally has a second bandpass filter for the second modulation frequency, so that the separation of the measuring signals takes place by means of the bandpass filter.

In a further preferred embodiment, the measuring signals are separated by means of a Fourier transformation, particularly preferably by means of a fast Fourier transformation (FFT). The measuring unit is therefore preferably designed for carrying out a Fourier transformation, in particular FFT, of the measuring signals.

When modulating by means of a phase modulation, the separation of the measurement signals depending on the respective modulation frequency in a conventional manner: It is preferably provided per se known phase filter so that separately on the one hand only portions of the measuring beam with the first phase and on the other hand only portions of the measuring beam evaluated in the second phase.

The device according to the invention of the method according to the invention is suitable for the spectrally resolved measurement of an object, in particular of photoelectric objects such as light sensors. In particular, the device according to the invention and the method according to the invention are suitable for the spectrally resolved measurement of a photovoltaic solar cell, in particular for determining the external and / or internal quantum efficiency of a photovoltaic solar cell.

The fundamental structure of a device for determining the quantum efficiency and for carrying out a corresponding measurement method is known per se, in particular from MA Green, "Solar Cells - Operating Principles, Technology and System Applications", Prentice-Hall, Inc. (Spectral response: pp 98 -100, Bernhard Fischer, "Let Analysis of Crystalline Silicon Solar Cells Using Photoconductivity and Quantum Efficiency Measurements", Dissertation, University of Konstanz, 2003, pp. 39-46 and Carsten Hampe, "Investigation of influenzated and diffused pn-transitions of terrestrial and Thermophotovoltaic silicon solar cells ", VDI-Verlag, VDI Series 9 No. 352 (2002), pp. 56-60. Preferably, the method and the device according to the invention are analogous to those formed in one or more of the sources cited here, wherein the light modulator unit as described above, or the light modulation is carried out as described above ,

Due to the high measuring speed, the device according to the invention and the method according to the invention are particularly suitable for use within a process line in the production of the solar cell for routine characterization.

Further preferred embodiments and preferred features are described below with reference to the figures and exemplary embodiments. Showing:

1 A first embodiment of a device according to the invention, in which the dismantling unit comprises an optical grating and

2 A second embodiment of a device according to the invention, in which the dismantling unit comprises two optical gratings.

The device according to the invention 1 is used for spectrally resolved measurement, in particular determination of the external quantum efficiency of a photovoltaic solar cell S. The device has a designed as a xenon lamp light source L. The output beam generated by the light source L 5 is coupled into a housing G, in which housing G, an optical decomposition unit and an optical light modulator unit are arranged.

The optical decomposition unit is used for the spectral decomposition of the output beam 5 and has concave parabolic levels 3 as well as an optical grid 2 on. The output beam 5 first meets a first parabolic mirror 3 , which serves as a collimator, so that the output beam is substantially parallelized to the optical grating 2 incident. The optical grid 2 is designed such that a spectral decomposition of the output beam takes place. Via a second parabolic mirror, the spectrally decomposed output beam is converted to a micromirror unit 4 formed light modulator unit shown.

By means of the micromirror unit 4 a modulation with a modulation frequency and modulation phase, wherein different micromirrors are each modulated with a different frequency, so that beam splitter, which at different locations on the micromirror unit 4 be correspondingly modulated with different modulation frequencies, This will be in a simple way by means of the optical grating 2 generated spectral sub-beams each assigned a different modulation types.

The at the micromirror unit 4 reflected and modulated spectral sub-beams are returned via the second parabolic mirror 3 on the optical grating 2 imaged and thereby combined into a beam, which in turn on the first parabolic mirror 3 and a deflection mirror U, which is designed as a planar mirror is guided to a measuring beam output, so that the measuring beam 6 meets the solar cell S.

The second embodiment according to 2 has a fundamentally comparable to the first embodiment construction. In the following, therefore, to avoid repetition, only the essential differences will be discussed. Same reference numerals in FIG 1 and 2 denote identical or equivalent elements.

In contrast to the first embodiment, the in 2 illustrated second embodiment of two optical grating 2A and 2 B on. The output beam generated by the light source L 5 will have a first parabolic mirror 3A on the first optical grating 2A collimated and there spectrally decomposed as described above and a second parabolic mirror 3B on the as a micromirror unit 4 formed light modulator unit shown. By means of the micromirror unit 4 As described above, a modulation of the spectral sub-beams with different modulation frequencies. The at the micromirror unit 4 however, reflected and frequency-modulated spectral sub-beams are transmitted via another parabolic mirror 3C on a second optical grating 2 B imaged, merged by means of this into a beam and a fourth parabolic mirror 3D deflected to a deflecting mirror U finally around as a measuring beam 6 impinging on the solar cell S to be measured.

The main difference in the use of an optical grating according to the first embodiment or two optical grids according to the second embodiment is that in the embodiment with a grating the cost factor for coupling and decoupling and the spectral decomposition of the measuring beam is reduced by half. In contrast, in the embodiment by means of two optical grating a simpler and independent adjustment of the incident and exiting measuring beam is made possible.

It can also be seen in FIG. 2 that by means of the first optical grating 2A the input beam 5 is divided into a plurality of spectral sub-beams (for ease of illustration only two are shown), which different surface areas of the second parabolic mirror 3B cover: A first spectral sub-beam covers the area F1 and a second spectral sub-beam covers the area F2. As a result, the first spectral sub-beam is at a point P1 and thus a first micromirror on the micromirror unit 4 and the second spectral sub-beam at a point P2 and thus a second micromirror on the micromirror unit 4 displayed. In reverse order this is done starting from the micromirror unit 4 , about the parabolic mirror 3C and the optical grating of the optical grating 2 , so that the (now differently modulated) spectral sub-beams are brought together again to form an optical beam.

In 1 the spatial distribution is analogous.

In the 1 and 2 For simplicity, only two spectral sub-beams are shown. However, typical embodiments have a multiplicity, for example 100 spectral sub-beams, which are correspondingly imaged on 100 different micromirrors and modulated with 100 mutually different modulation frequencies. In the in the 1 and 2 The half-width of each spectral sub-beam is 1 nm. The spectral sub-beams have in this case pairs of different maxima, the maxima covering a frequency range from 200 Hz to 2 kHz approximately equidistantly.

Claims (15)

Device for a spectrally resolved measurement of an object, comprising a light source (L) for generating a broadband output beam, an optical decomposition unit for spectrally splitting the output beam into at least a first and a second spectral sub-beam, a light modulator unit for modulating the first and second spectral sub-beam and an optical Merging unit for merging the modulated spectral sub-beams into a measuring beam, and with a measuring unit for recording measurement signals of the measuring beam ( 6 ) , in which the light modulator unit is designed to modulate the first spectral sub-beam with a first modulation type and the second spectral sub-beam with a second modulation type, wherein the first and second types of modulation are different and in that the measuring unit is designed, first measuring signals, which with the first modulation type are modulated and second measurement signals which are modulated with the second modulation type to separate. Apparatus according to claim 1, characterized in that the decomposing unit comprises an optical prism. Device according to one of the preceding claims, characterized in that the dismantling unit is an optical grating ( 2 ), Device according to Claim 3, characterized in that the optical grating ( 2 ) and the light modulator unit are designed and arranged to cooperate in such a way that the output beam spectrally separated by the grating ( 5 ) strikes the light modulator unit and the at least two modulated spectral sub-beams strike this grating again. Apparatus according to claim 3, characterized in that the decomposing unit comprises at least a first and a second optical grating ( 2 ) which are designed and arranged to cooperate with the light modulator unit in such a way that the output beam spectrally decomposed by the first grating ( 5 ) impinges on the light modulator unit and the at least two modulated spectral sub-beams strike the second grid. Device according to one of the preceding claims, characterized in that the decomposing unit comprises a collimator and a dispersive element in order to control the output beam ( 5 ) collimated onto the dispersive element, in particular that the collimator has a concave mirror, preferably a parabolic mirror ( 3 ). Device according to one of the preceding claims, characterized in that the breaking unit and light modulator unit are formed cooperatively such that at least 10, preferably at least 20, more preferably at least 30 spectral sub-beams with different modulation types, preferably in pairs different modulation types are modulated. Device according to one of the preceding claims, characterized in that the modulation is a frequency modulation in that the first spectral part with a first modulation frequency and the second spectral part are modulated with a second modulation frequency, wherein first and second modulation frequency are different, in particular that the measuring unit at least a first bandpass filter for the first modulation frequency, preferably additionally comprises a second bandpass filter for the second modulation frequency, in particular that the measuring unit comprises a LockIn amplifier and / or that the measuring unit is designed for performing a Fourier transformation of the measurement signals. Device according to one of the preceding claims, characterized in that the modulation is a phase modulation by the first spectral part with a first phase change and the second spectral part are modulated with a second phase change, wherein first and second phase change are different, in particular that the measuring unit at least comprises a first phase filter for the first phase change, preferably additionally a second phase filter for the second phase change, Device according to one of the preceding claims, characterized in that the device for determining the spectral sensitivity of an optoelectronic element, in particular a solar cell (S) is formed. A method for the spectrally resolved measurement of an object, comprising the following method steps: A generating a broadband output beam and spectrally splitting the output beam into at least a first and a second spectral sub-beam; B modulation of the first and second spectral sub-beam by means of a light modulator unit; C merging the first and second spectral sub-beams into a measuring beam; D applying the measuring beam to the object ( 6 ) and E measuring a measurement signal of the object; characterized in that in method step B, the first spectral part is modulated with a first modulation type and the second spectral part with a second modulation, wherein first and second types of modulation are different and that in step E the measurement signal is processed by first measurement signals, which with the first Modulationsart are modulated and second measurement signals which are modulated with the second modulation type are separated A method according to claim 11, characterized in that in method step E, the first and second measuring signals are separated by means of at least one bandpass filter, preferably by means of at least two bandpass filters, in particular that the separation takes place by means of a LockIn method. A method according to claim 11, characterized in that in step E, the first and second measurement signals are separated by Fourier transformation. Method according to one of claims 11 to 13, characterized in that takes place in step A of the spectral decomposition of the output beam by means of an optical grating, in particular, that after modulation according to method step B, the two spectral sub-beams impinge again on the optical grating. Method according to one of claims 11 to 14, characterized in that a spectral sensitivity of the object is determined.

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