Title of Invention

"DEVICE AND METHOD FOR ABLATING THIN-FILM LAYER AND A METHOD OF FORMING A SOLAR CELL"

Abstract The invention relates to a device and a method for removing thin layers on a support material, especially for removing barrier layers of a thin-layer solar cell. The aim of the invention is to provide an economical means of removing strips of upto a few millimetres in width without damaging the substrate of the thin-layer solar cell underlying the layer to be removed. To this end, a laser treatment device with a laser resonator and an optical system is provided. The optical system projects the treatment beam produced by the layer resonator over an area of 1 mm2 to 1 cm2 on the surface to be trreated with an essentially homogenous distribution of power. Thin layers can be effectively removed from the substrate at pulse width of less than 100 ns. and with a pulse energy density of 0.1 J/cm2 to 10 J/cm2.
Full Text DEVICE METHOD FOR ABLATING THIN-FILM LAYER AND A METHOD
FOR ABLATING THIN-FILM LAYER AND A METHOD OF FORMING
A SOLAR CELL
The invention relates to a method and device for thin-film ablation of a substrate, for example, in this case for delamination of laminated ceramics or glasses. More particularly the invention is intended for surface layer ablation of a thin-film solar cell In addition the invention relates to a method for encapsulating a thin-film solar module comprising a thin-film laminated substrate.
Conventional solar modules of crystalline silicon are based on wafer fabrication with subsequent electrical wiring, resulting in relatively small power unit of apporx 1w silicon wafers then needing as a rule to be circuited into 50 -100 W modules

As an alternative to these conventional solar modules thin-film solar cells have become known on the basis of micrometer film thicknesses. The substantial elemen|s of a thin-film solar cell are shown in Fig. 2 and consist of a p/n junction between the absorber layer and the window layer.
Unlike conventional silicon wafer wiring, thin-film cells can be circuited integrated: following the individual coating steps on the total surface area a) the back electrode b) the sandwiched cell and c) the front electrode are sliced into longitudinal strips. Staggering these three slices relative to each other forms an electrical connection between cells adjoining the front and back electrode. Slicing may be done by scribing or laser slicing in permitting cost-effective fabrication of a standard solar module for 12 V applications on a size of approx. 0.5 x 0.5 m2, for example.
The useful life of such a solar module is substantially dictated by how well the thin-film layers are protected from the weather and environment. Achieving a long life of 30 years and more requires the thin-film layers to withstand extreme exposure to sunlight, moisture and air pollutants. The requirements as to moisture stability and voltage strength can thus only be satisfied when the thin-film solar cell insufficiently encapsulated and the current-carrying components are adequately insulated electrically.

For this purpose the current-carrying components of a thin-film solar cell are encapsulated laminated. Encapsulation is achieved in that, after coating the substrate with the current-carrying film layers, the surface portion of the substrate is delaminated and a laminate then deposited on the complete film-layer. This results in laminate and substrate being surface bonded resistant to corrosion in thus reliably protecting internal portions from moisture degradation.
To make this clear, Fig. 1 is a diagrammatic representation of a section through an encapsulated solar cell, showing how patterned film-layers 3 deposited on the substrate 4 are delaminated in the surface areas 5 and encapsulated by a laminate layer 2. Deposited over the laminate layer 2 is a layer of window glass 1.
One problem in making such an encapsulating of a thin-film solar cell is delaminating the thin-film surface layers. Conventional methods of delamination, such as for instance sandblasting or delamination by grinding unavoidably also result in damage to the substrate surface and in the formation of microcracks therein. The great differences in temperature in a thin-film module once in operation and the resulting tensile stresses add to the risk of fracture and ultimately to the solar cell being damaged due to cracks forming in the surface. Accordingly, surface delamination needs to be undertaken with particular care in the surface usually a few millimeters to centimeters wide.
Chemical methods of ablation are known in principle for machining solar cells which, however, have the drawback of lengthy machining times and involve complicated steps in machining.
This is why removing the surface areas as described continues to be done by mechanical methods such as grinding or sandblasting since these methods permit precisely defining material ablation. In addition to the damage done to the substrate surface and the formation of microcracks as already described, these methods have the additional drawback that the workpiece as a rule needs to be subsequently chemically cleaned in an ultrasonic bath since the plume of the ablated film-layers soils the module undesirably.
It is known furthermore to produce the steps as described above for integrated circuiting a thin-film solar module by a laser beam for interconnecting the resulting individual strips in series.

Known, for example, from US 4,734,550 is a method for machining thin-film layers with a laser, one special application cited being machining photoelectric film-layers generated by thin-film technology. The objective of the machining method is to notch the thin-film layers by directing the machining beam on the surface of each workpiece so that the power distribution applied at the time remains as homogenous as possible. This is achieved by a rectangularly focussed beam having a flat intensity distribution, steering the beam controlled being additional such that the overlapping portions of the rectangularly focussed beam results in an intensity distribution as uniform as possible. This method is said to permit notching to a precise and even depth for series circuiting solar cells.
The objective of all methods for series circuiting solar cells is to attain a track width as narrow as possible for minimum electric power degradation of the solar module, track widths of the order of 50 urn being cited, for example, in US 4,734,550.
Supplementary thereto, optimum power densities are cited in Nakano, S., et al., "Laser Patterning Method for Integrated Type a-Si Solar Cell Submodules, in: Jap. J. of Appl. Phys. Vol. 25, No. 12,1986, pages 1936-1943 for laser beam machining solar modules in obtaining series circuiting. In this case, power densities of the order of 1 . 106 W/cm2 are cited suitable for a track width of 50 m.
Since, as aforementioned, the delamination methods for series circuiting has the objective of attaining a minimum track width, they are unsuitable for surface delamination of solar modules, since for this application surface strips a few millimeters wide need to be delaminated. This is why the aforementioned mechanical methods are used, now as then, despite the aforementioned drawbacks, for surface delamination.
It is thus the objective of the invention to provide a device and a method for thin-film ablation of a solar cell permitting cost-effective ablation of strips up to a few millimeters wide without damaging the substrate located beneath the layer to be ablated.
This objective is achieved by a device having the features as set forth in claims 1 to 11 and by a method having the features as set forth in claims 12 to 22.

In addition, the device in accordance with the invention can be put to use advantageously in a method for encapsulating a thin-film solar module as set forth in claim 23.
The invention is based on having discovered that, contrary to applications known hitherto, laser ablation can also be put to use surprisingly for ablation widths in the millimeter range. As compared to methods for series circuiting solar cells, the machining surface area of the laser beam is expanded via a suitable optical system in a range of approximately 1 mm2 up to 1 cm2 (i.e. several magnitudes higher). Surprisingly, results have shown that even when expanding the machining beam to this extent, relatively thin-film delamination of a substrate is still possible when light pulses of the machining beam are generated with pulse durations smaller than 100 ns and a pulse energy density in the range 0.1 J/cm2 to 10 J/cm2. It appears to have been assumed that in such an expansion of the machining beam the irradiated energy can no longer be sufficiently absorbed. The ablation process is namely still lacking a full explanation also for the tracks widths used in series circuiting. It seems that the light pulses generate in the topmost micrometers of the thin-film a plasma whose expansion entails a shock wave. The heated material is thus subjected to a high internal pressure so that plasma particles are ejected from the irradiated site. In this respect it could not be anticipated that in expanding the machining beam several magnitudes larger similar good effects can still be attained when the remaining surface parameters are selected in suitable ranges. Decisive, in addition, is that the power distribution in the machining beam is configured substantially homogenous. Although a Gaussian power distribution can usually be assumed for the machining beam, the invention teaches that the optical system needs to be configured so that an homogenous power distribution results in broad ranges over the surface area being machined. Otherwise no satisfactory ablation results could be achieved in expanding the machining beam in accordance with the invention.
To attain the ablation results in accordance with the invention it has furthermore been found out in the invention that the machining beam needs to be moved relative to the workpiece so that each unit of surface area of the workpiece to be ablated receives a substantial constant amount of energy.
With the device in accordance with the invention it is now more particularly possible to cost-effectively encapsulate a thin-film solar module comprising a substrate coated with thin-film layers. In this arrangement the substrate is accordingly first coated over the full surface area with thin-film layers of the order of a few m. Then, using the

Amended Pages 5, 5a, 5b
Supplementary thereto, optimum power densities are cited in Nakano, S., et al., ,,Laser Patterning Method for Integrated Type a-Si Solar Cell Submodules, in: Jap. J. of Appl. Phys. Vol. 25, No, 12,1986, pages 1936-1943 for laser beam machining solar modules in obtaining series circuiting. In this case, power densities of the order of 1 . 106 \V/cm2 are cited suitable for a track width of 50 urn.
Since, as aforementioned, the delamination methods for series circuiting has the objective of attaining a minimum track width, they are unsuitable for surface delamination of solar modules, since for this application surface strips a few millimeters wide need to be delaminated. This is why the aforementioned mechanical methods are used, now as then, despite the aforementioned drawbacks, for surface delamination.
US 5,151,135 discloses a device for cleaning the surfaces of solar cells and other means, it comprising a laser resonator for generating a light pulse machining beam having pulse durations smaller than 100 ns and a pulse energy density in the range 0.1 J/cm2 to 10 J/cm2, an optical system for imaging the machining beam generated by the laser resonator on the surface to be cleaned over a surface area in the range of 1 mm2 to a few cm2 with a substantially homogenous power distribution, a first positioner for a predefined relative movement between the surface to be cleaned and the machining beam, and including a controller for signalling the first positioner such that each unit of surface area is beamed with a substantially constant amount of energy.
JP 10 052 780 A discloses a device for thin-film ablation of a thin-film solar cell comprising a laser resonator for generating a light pulse machining beam, an optical system comprising a lens and a pin-hole diaphragm for imaging the machining beam generated by the laser resonator on the surface to be machined over a surface area in the range of a 1 mm" to 1 cm" with a substantially homogenous power distribution, a first positioner for a predefined relative movement between the workpiece and the machining beam, and including a controller for signalling said first positioner such that each unit of surface area is beamed with a substantially constant amount of energy.

The invention is based on the objective of providing a device and a method for thin-film ablation of a solar cell permitting cost-effective ablation of strips up to a few
millimeters wide without damaging the substrate located beneath the layer to be ablated.
In accordance with the invention, this objective is achieved as taught by the claims 1 and 13 respectively.
Further aspects of the invention read from the claims subordinate to each of these claims.

machining angle. More particularly, in the case of a thin-film configuration as shown in Fig. 2 a machining angle was found by mechanisms which are still awaiting satisfactory explanation for permitting ablation of the film-layer of the front electrode and absorber layer with no degradation of the back electrode.
To permit reproducible settings of the machining angle as established in trial and error, it is provided for in accordance with a preferred embodiment to enable the second positioner to be likewise signaled by the controller, it more particularly being provided for that the controller comprises a memory and input unit. An optimum machining angle is memorized for each type of delamination process in the memory and on inputting a type of a delamination process into the input unit the corresponding control signals for an optimum machining angle; are communicated from the controller to the second positioner.
In exposing a back electrode of a thin-film solar cell it has been discovered that preferably an angle in excess of 0°, more particularly between 5° and 10° needs to be selected. It is assumed that inclining the optical axis to the incidence perpendicular results in the film-layers located beneath the layer to be ablated have a lesser tendency to absorb the laser beams so that these film-layers remain totally free of degradation.
For total ablation of all film-layers it has been discovered to be good practice to select the so-called Brewster angle as the optimum machining angle, especially when the machining beam is suitably polarized, the tangent of the Brewster angle equaling the diffraction number of the layer to be ablated.
In accordance with another preferred embodiment it is provided for that the light pulses are generated by modulating the pumping power. By modulating the pumping power for the active medium of a laser, the machining parameters in accordance with the invention can still be made available cost-effectively with pulse durations of just less than 100 ns. Shorter light pulses and higher power is achievable, however, by the Q modulation method. This enables light pulses to be made available of the order of 10 ns with sufficient power. For some applications, pulse durations of the order of 25 ns have also proven to be particularly of advantage. To achieve even shorter pulse times, recourse can be made, in conclusion, to the so-called mode coupling method.
In accordance with yet another preferred embodiment it is provided for that the machining beam for mode mixing is communicated via an optical fiber so that a power

profile having approximately the shape of a truncated cone materializes for the power distribution. Mode mixing in the optical fiber translates the known Gaussian power profile into a trapezoidal or, as viewed three-dimensionally, truncated cone, power profile.
In accordance with another preferred embodiment it is provided for that the speed with which the relative movement advances and the pulse repetition rate of the light pulses are adapted so that a unit of surface area is no longer beamed by the machining beam as soon as the film-layer to be ablated has been removed. For example, the first positioner may be signaled such that the relative movement produces a traveling speed of the order of 1 cm/s for a pulse repetition frequency of the laser resonator of around 50 Hz.
It has been discovered to be particular good practice to beam a unit of surface area substantially with but a single light pulse or at least with but a few light pulses. The material of a unit of surface area to be ablated should thus be substantially "spalled" by a single light pulse with minimum degradation of the substrate underneath.
The wavelength of the laser resonator needs to be adapted to the film-layer to be ablated such that the light pulses are substantially absorbed thereby and not absorbed by the substrate material. In delaminating thin-film solar cells good results have been obtained, for example, with a Nd:YAG-type laser resonator having wavelength of 1.064 urn.
In yet another preferred embodiment a suction exhaust device for exhausting resulting dusts and vapors is provided in protecting personnel therefrom and, for example, avoiding deposits thereof on the workpiece which could degrade the surface quality of the film-layer to be exposed.
In a final preferred embodiment it is provided for that the first positioner consists of means for mechanically steering the machining beam together with the optical system over the workpiece. In this case the workpiece accordingly remains stationary whilst the optical means is movably steered. For this purpose the machining beam is communicated to advantage via an optical fiber cable. As an alternative it is however conceivable that the first positioner consists of adjustable deviating mirrors via which the machining beam is steered to the workpiece. The deviating mirror assembly may include, for example, two deviating mirrors, the axes of rotation of which are located perpendicular to each other so that the machining beam can be simply moved over a

larger plane. In addition, it is also possible to mount the optical system stationary whilst the workpiece is guided, for example on an xy table, relative to the fixed machining beam. In conclusion, combinations of the aforementioned systems are conceivable in which both the machining beam and the workpiece are movably guided.
In addition to being used for delamination of thin-film solar cells the device in accordance with the invention may, of course, be put to use for the delamination of all thin-film coated glasses or ceramics; further applications accordingly possibly being:
modem insulated window glazing, so-called "k glasses" comprise additional vacuum deposited layers to reduce the transparency of the glazing to thermal radiation. Typical insulated glazing comprises at least two panes bonded in a frame profile into a dual pane so that, here too, surface delamination is needed;
a wealth of delamination processes are likewise involved in all aspects of display systems;
in conclusion, further applications come into consideration in which coated glazing needs to be further processed, one example of which are so-called "switchable windows" which change their transparency to light on applicantion of an electrical field.
Accordingly, the present invention provides a device for ablating at least one

thin-film layer selected from the group having a front electrode, amabsorber layer

and a back electrode of a substrate of a workpiece, comprising : a laser resonator for generating a light pulse machining beam having pulse durations smaller than 100 ns and a pulse energy density in a range 0.1 J/cm2 to 10 J/cm2; an optical system arranged in a path of the machining beam, the optical system having an optical fibre cable serving mode mixing and an optical imaging member for imaging an output of the optical fibre cable on a surface of the workpiece to be machined, and configured such that, in a plane of the surface to be machines, power distribution in a surface area range of 1 mm2 to 1cm2 is substantially homogenous ; and a positioner, controllable by a controller, for positioning the workpiece relative to the machining beam such that for a relative movement an amount of energy impinging the surface to be machined is substantially constant for each unit of surface area.

-8A-
The present invention also provides a method for ablating at least one thin-film layer selected from the group having a front electrode, an absorber layer and a back electrode of a substrate of a workpiece, comprising the steps of: generating a light pulse machining beam having pulse durations smaller than 100 ns and a pulse energy density in a range 0.1 J/cm2 to 10 J/cm2, communicating the machining beam via an optical fibre cable that serves mode mixing ; imaging an output of the optical fibre cable on a surface of the workpiece to be machined such that, in a plane of a surface to be machined, power distribution in a surface area of 1 mm2 to 1cm2 is substantially homogenous ; and positioning the workpiece relative to the machining beam such that for relative movement, an amount of energy impinging the surface to be machined is substantially constant for each unit of surface area.
The present invention further, provides a method of forming a solar cell,
comprising the steps of : coating a substrate with at least one thin film-layer ; performing a thin-film ablation of the substrate, comprising : generating a light pulse machining beam having pulse durations smaller than 100 ns and a pulse energy
density in a range 0.1 J/cm2 to 10 J/cm2, communicating the machining beam via an optical fibre cable that serves mode mixing ; imaging an output of the optical fibre cable on a surface of the substrate such that, in a plane of the surface, power distribution in a surface area range of 1 mm2 to 1 cm2 is substantially homogenous ; and positioning the substrate relative to the machining beam such that for a relative movement an amount of energy impinging the surface is substantially constant for each unit of surface area ; covering the at least one thin-film layer with a laminate that encapsulates the substrate, thereby forming the solar cell.

8B
The invention will now be detailed by way of various example embodiments with reference to the attached drawings in which:
Fig. 1 is a cross-section through an encapsulated thin-film solar cell,
Fig. 2 is a cross-section through an encapsulated thin-film solar cell showing the film-layer sequence and contacting of the back electrode,
Fig. 3 is a diagrammatic representation of a first embodiment of a device for delaminating solar cells and
Fig. 4 is a diagrammatic representation of a second embodiment of a device for delaminating solar cells.

9


Referring now to Fig. 1 there is illustrated a cross-section through an encapsulated thin-film solar cell. The solar cell substantially consists of a substrate 4, the film-layers 3 deposited and patterned thereon, a laminate layer 2 and a layer of window glass applied thereto. The current-carrying film-layers 3 have a thickness in the range 0.1 to 5 urn and the substrate 4 is preferably made of float glass. To eliminate current paths to the current-carrying film-layers 3 and a moisture degradation of the film-layers themselves the surface region 5 of the substrate 4 must not contain any current-carrying layers. This is why the surface region 5 is delaminated in accordance with the invention.
Referring now to Fig. 2 there is illustrated a cross-section through an encapsulated thin-film solar cell showing the film-layer sequence and contacting of the back electrode. In substrate thin-film solar cells the film-layer sequence is made up of the back electrode 24, the absorber layer 23 and the front electrode 22. The film-layers are deposited on the substrate 25 and protected at the front electrode 22 side by the laminate 21. The laminate 21 is closed off by a layer 20 of window glass.
Marked in Fig. 2 are two sites A and B representing the various results of possible delamination processes in the case of a thin-film solar cell.
In site A a complete delamination of the substrate has been undertaken with no degradation of the remaining surface of the substrate itself. In site B a selective delamination of the front electrode and absorber layer has been undertaken so that the back electrode is left standing. For contacting the back electrode the film-layers thereabove need to be selectively removed without any substantial degradation of the back electrode itself. The exposed sites are then contacted with metal bands 26.
When removing the film-layers above the sites to be contacted the light needs to be incident at the film-layer side of the front electrode 22.
For assessing the quality of the delamination process, metal bands were applied to the exposed back electrode sites using a current standard contacting process. The good bond of the bands showed that the delamination in accordance with the invention with a laser device is also suitable for exposing the sites of the back electrode to be contacted, this thus replacing mechanical delamination also in the case of exposing the back electrode.

10
Referring now to Fig. 3 there is illustrated a first embodiment of a device for dela-minating solar cells. Delamination was done with a pulsed ND:YAG-type laser. Preferably the laser resonator is operated by the Q modulation method with a pulse duration of the order of 25 ns. The machining beam is communicated with the aid of an optical fiber cable 40 to an imaging optical system including a focussing lens 34. The output 35 of the optical fiber cable 40 is imaged via the focussing lens 34 on the workpiece 31 in the machining site 41.
In this configuration the pulse energy density at the workpiece materializes from the pulse energy of the laser, the optical losses and the imaging scale of the optical system employed. The necessary pulse energy density as well as the speed at which the laser beam is traveled relative to the workpiece to be delaminated for a given power distribution depends on the laminate to be removed. For example, the laminates of thin-film solar modules tested permitted removal with pulse energy densities of the order of 1 J/cm2 with a traveling speed of the order of 1 cm/s and a pulse frequency of 50 Hz. .
In delaminating the back electrode as shown in Fig. 2, the necessary pulse energy density as well as the speed at which the laser beam is traveled relative to the workpiece to be delaminated for a given pulse frequency likewise depends on the laminate involved. Successful delamination of the back electrode of thin-film solar modules was achieved, for example, with pulse energy densities of the order of 1 J/cm2 with a traveling speed of the order of 3 cm/s and a pulse frequency of 50 Hz.
Evident from Fig. 3 is how the workpiece 31 is mounted by a corresponding tool holder 32 which may be, for example, a vacuum clamping bench. The tool holder 32 is in turn mounted on a CNC xy table 33. The table 33 including the tool holder 32 and the work-piece 31 can be traveled at constant speed so that the machining site 41 for delaminating the solar cell 31 is movable along a defined distance. Resulting vapors and dusts are exhausted via suction exhaust devices 36, 38. For special applications nozzles 37, 39 are provided to protect the surface to be exposed from oxidation or other chemical reactions with the atmosphere. In this case, particularly nitrogen proved to be a suitable inert gas. The nozzles 37, 39 are set so that at the machining site an even flow of the inert gas over the surface of the workpiece is assured.
Optimum machining results are attained when the optical axis 46 of the imaging optics is set to a machining angle to be defined as an optimum for the particular application relative to the incidence perpendicular 43, tilt angles in the range 5° to 10° having

11
proven to be particularly favorable in the case of exposing a back electrode of a thin-film solar cell.
Referring now to Fig. 4 there is illustrated a second embodiment for delaminating solar cells. The mounting configuration of the solar cell 31 as evident from the first embodiment was retained, it being identified by the same reference numerals. The substantial difference of the second embodiment as shown in Fig. 4 as compared to the first embodiment is that delamination as shown in Fig. 4 is in the region of the bottom substrate layer.
This application comes into consideration in all processes for delaminating solar cells involving a light-transparent substrate which needs to be totally exposed in defined areas. Whilst fine hair cracks materialized in the delaminated site with light incidence at the coated side, the glass substrate with light incidence at the substrate side permitted delamination with no degradation of the substrate as evident under an optical microscope.
Otherwise the optical configuration is the same as that of the first embodiment so that likewise the machining beam is communicated via a optical fiber cable 50 to an imaging optical system including a focussing lens 54 which, in turn, images the output portion 55 of the optical fiber cable 50 on the workpiece 31 in the machining site 51.
In the delamination method in accordance with the second embodiment good results were attained, for example, when the machining angle of the optical axis 56 was set to the incidence perpendicular.
In the second embodiment too, dusts and vapors generated during lasering are exhausted. Subsequent cleaning is necessary neither for the substrate side variant nor for the laminate side variant in applying the delamination methods as employed hitherto. Both variants of the novel laser delamination system are thus to be given preference over existing mechanical systems.
It is to be noted in particular as regards the second embodiment as shown in Fig. 4, however, that fully machining the solar cell at the substrate side may require corresponding cutouts to be provided in the xy table 33 and tool holder 32 so that the machining beam is unobstructed in attaining all sites of the solar cell to be delaminated.

12
More particularly for products in which even the finest of microcracks in the substrate could pose a problem, the variant having light incidence at the substrate side should be employed. In less critical applications as regards microcracks in the substrate - or where other substrate types are concerned - delamination with the simpler arrangement of mounting the workpiece is possible with light incidence at the coated side. It is also particularly advantageous when the methods in accordance with these embodiments can be suitably combined. Thus, for example, the fracture-sensitive surface sites of the substrate can be delaminated in accordance with the second embodiment at the substrate side, since these surface sites have facilitated access in this case too in thus eliminating the need for cutouts in the tool holder and in the clamping table, whereas delamination in accordance with the first embodiment can be done at the coated side where central sites require delamination in special applications.
14

-13-
WE CLAIM :
1. A device for ablating at least one thin-film layer selected from the group having
a front electrode, an absorber layer and a back electrode of a substrate of a
workpiece, comprising:
a laser resonator for generating a light pulse machining beam having pulse durations smaller than 100 ns and a pulse energy density in a range 0.1 J/cm2 to 10 J/cm2;
an optical system arranged in a path of the machining beam, the optical system having an optical fibre cable serving mode mixing and an optical imaging member for imaging an output of the optical fibre cable on a surface of the workpiece to be machined, and configured such that, in a plane of the surface to be machines, power distribution in a surface area range of 1 mm2 to 1cm2 is substantially homogenous ; and
a positioner, controllable by a controller, for positioning the workpiece relative to the machining beam such that for a relative movement an amount of energy impinging the surface to be machined is substantially constant for each unit of surface area.
2. The device as claimed in claim 1, wherein the workpiece is a thin film solar
cell.
3. The device as claimed in claim 1, wherein the laser resonator generates the
light pulse machining beam by modulating a pumping power of the laser resonator.
4. The device as claimed in claim 1, wherein the laser resonator generates the
light pulse machining beam by Q modulation.

-14-
5. The device as claimed in claim 1, wherein the pulse durations are
approximately 25 ns.
6. The device as claimed in claim 1, wherein a relative advancing speed of the
positioner is approximately 1 cm/s, and light pulses of the light pulse machining
beam are generated by the laser resonator with a pulse repetition frequency of
approximately 50 Hz.
7. The device as claimed in claim 1, wherein a relative advancing speed of the
positioner and a pulse repetition frequency of light pulses in the machining beam are
adapted to each other such that a unit of surface area of the surface of the workpiece
to be machined is beamed by a single or few light pulses.

8. The device as claimed in claim 1, wherein a wavelength of the machining
beam generated by the laser resonator is such that the machining beam is
substantially absorbed by a film-layer of the workpiece to be ablated and is
substantially not absorbed by the substrate of the workpiece.
9. The device as claimed in claim 8, wherein the laser resonator is a ND:YAG-
type laser resonator having a wavelength of 1.064 micrometer.
10. The device as claimed in claim 1, wherein the optical imaging member is
variably adjustable for changing an angle of its optical axis relative to the plane of the
surface of the workpiece to be machined.
11. The device as claimed in claim 1, wherein a suction exhaust means is
provided in a vicinity of an effective site of the machining beam.

-15-
12. The device as claimed in claim 1, wherein a nozzle means for supplying an
inert gas is provided in a vicinity of an effective site of the machining beam.
13. A method for ablating at least one thin-film layer selected from the group
having a front electrode, an absorber layer and a back electrode of a substrate of a
workpiece, comprising the steps of:
generating a light pulse machining beam having pulse durations smaller than 100 ns and a pulse energy density in a range 0.1 J/cm2 to 10 J/cm2, communicating the machining beam via an optical fibre cable that serves mode mixing ;
imaging an output of the optical fibre cable on a surface of the workpiece to be
machined such that, in a plane of a surface to be machined, power distribution in a
surface area of 1 mm2 to 1cm2 is substantially homogenous ; and
positioning the workpiece relative to the machining beam such that for relative movement, an amount of energy impinging the surface to be machined is substantially constant for each unit of surface area.
14. The method as claimed in claim 13, wherein the workpiece is a thin-film solar
cell.
15. The method as claimed in claim 13, wherein generating the light pulse
machining beam comprises modulating a pumping power of a laser resonator that
generates the light pulse machining beam.
16. The method as claimed in claim 13, wherein generating the light pulse
machining beam comprises generating light pulses by Q modulation.

-16-
17. The method as claimed in claim 13, wherein generating the light pulse
machining beam comprises generating light pulses having a pulse duration of
approximately 25 ns.
18. The method as claimed in claim 13, wherein :
positioning the workpiece comprises advancing the workpiece relative to the machining beam at a speed of approximately 1 cm/s ; and generating the light pulse machining beam comprises generating light pulses with a pulse repetition frequency of approximately 50 Hz.
19. The method as claimed in claim 13, compnsing an act of adapting a relative
speed between the workpiece and the machining-beam and a pulse repetition
frequency in the machining beam to each other; such that a unit of surfafce area of
the workpiece surface to be machined is beamed by a single or few light pulses.
20. The method as claimed in claim 13, wherein generating the machining beam
comprises generating a machining beam having a wavelength such that the
machining beam is substantially absorbed by a film-layer of the workpiece to be
ablated and is substantially not absorbed by the substrate of the workpiece.
21. The method as claimed in claim 20, wherein generating the light pulse
machining beam comprises generating the light pulse machining beam with a
ND:YAG-type laser resonator having a wavelength of 1.064 micrometer.
22. The method as claimed in claim 13, comprising variably adjusting an angle of
the machining beam relative to the plane of the surface of the workpiece to be
machined.

-17-
23. A method of forming a solar cell, comprising the steps of:
coating a substrate with at least one thin film-layer;
performing a thin-film ablation of the substrate, comprising : generating a light pulse machining beam having pulse durations smaller than 100 ns and a pulse energy density in a range 0.1 J/cm2 to 10 J/cm2, communicating the machining beam via an optical fibre cable that serves mode mixing ;
imaging an output of the optical fibre cable on a surface of the substrate such that, in a plane of the surface, power distribution in a surface area range of 1 mm2 to 1 cm2 is substantially homogenous ; and
positioning the substrate relative to the machining beam such that for a relative movement an amount of energy impingirig the surface is substantially constant for each unit of surface area ; covering the at least one thin-film layer with a laminate that encapsulates the substrate, there by forming the solar cell.


24. A device for ablating at least one thin-film layer, substantially as herein
described, particularly with reference to and as illustrated in the accompanying
drawings.
25. A method for ablating at least one thin-film layer, substantially as herein
described, particularly with reference to the accompanying drawings.
26. The method of forming a solar cell, substantially as herein described,
particularly with reference to the accompanying drawings.
The invention relates to a device and a method for removing thin layers on a support material, especially for removing barrier layers of a thin-layer solar cell. The aim of the invention is to provide an economical means of removing strips of upto a few millimetres in width without damaging the substrate of the thin-layer solar cell underlying the layer to be removed. To this end, a laser treatment device with a laser resonator and an optical system is provided. The optical system projects the treatment beam produced by the layer resonator over an area of 1 mm2 to 1 cm2 on the surface to be trreated with an essentially homogenous distribution of power. Thin layers can be effectively removed from the substrate at pulse width of less than 100 ns. and with a pulse energy density of 0.1 J/cm2 to 10 J/cm2.

Documents:

in-pct-2001-01030-kol abstract.pdf

in-pct-2001-01030-kol assignment.pdf

in-pct-2001-01030-kol claims.pdf

in-pct-2001-01030-kol correspondence.pdf

in-pct-2001-01030-kol description(complete).pdf

in-pct-2001-01030-kol drawings.pdf

in-pct-2001-01030-kol form-1.pdf

in-pct-2001-01030-kol form-13.pdf

in-pct-2001-01030-kol form-18.pdf

in-pct-2001-01030-kol form-3.pdf

in-pct-2001-01030-kol form-5.pdf

in-pct-2001-01030-kol g.p.a.pdf

in-pct-2001-01030-kol letters patent.pdf

in-pct-2001-01030-kol priority document others.pdf

in-pct-2001-01030-kol priority document.pdf

in-pct-2001-01030-kol reply f.e.r.pdf

IN-PCT-2001-01030-KOL-FORM-27.pdf

IN-PCT-2001-1030-KOL-CORRESPONDENCE.pdf

IN-PCT-2001-1030-KOL-FORM 27-1.1.pdf

IN-PCT-2001-1030-KOL-FORM 27.pdf

IN-PCT-2001-1030-KOL-FORM-27.pdf


Patent Number 202615
Indian Patent Application Number IN/PCT/2001/1030/KOL
PG Journal Number 09/2007
Publication Date 02-Mar-2007
Grant Date 02-Mar-2007
Date of Filing 03-Oct-2001
Name of Patentee SHELL SOLAR GMBH
Applicant Address FRANKFURTER RING 152, 80807 MUNCHEN
Inventors:
# Inventor's Name Inventor's Address
1 VOGT HELMUT KNORRSTRASSE 83B ,80807 MUNCHEN
2 KARG FRANZ JUNKERSTRASSE 20, 80689 MUNCHEN
PCT International Classification Number B 23 K 26/00
PCT International Application Number PCT/RP00/03132
PCT International Filing date 2000-04-07
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 199 33 703.9 1999-07-19 Germany
2 199 15 640.9 1999-04-07 Germany
3 199 27 529.7 1999-06-16 Germany