SOLAR CELL AND AN ARRANGEMENT AND A METHOD FOR PRODUCING A SOLAR CELL

Abstract

The present invention relates generally to solar cells, material layers within solar cells, a production method of solar cells, and a manufacturing arrangement for producing solar cells. A solar cell according to the invention includes at least one layer with a surface, produced by laser ablation, wherein the uniform surface area to be produced includes at least an area 0.2 dm2 and the layer has been produced by employing ultra short pulsed laser deposition wherein pulsed laser beam is scanned with a rotating optical scanner including at least one mirror for reflecting the laser beam.

Description

FIELD OF INVENTION

The present invention relates generally to solar cells, material layers within solar cells, a production method of solar cells, and a manufacturing arrangement for producing solar cells. More specifically, the present invention relates to what is disclosed in the preamble of the independent claim.

BACKGROUND

Solar cells provide an ecological way of producing energy, and they have therefore been under intensive development. Solar cells are generally made of photovoltaic cells. A photovoltaic cell has a at least one semiconducting layer, wherein photons of light are absorbed. The absorption of light causes electrons or holes to transfer to a higher, conducting energy level, and this energy can be used as electricity.

In order to conduct the formed electricity out of the solar cells there must be a conducting layer at the both sides of the semiconducting layer(s). The conducting layer at the radiated surface of the solar cell must allow light to enter the semiconductor layer. A solar cell is usually partitioned into small cells which are connected in series or parallel. In this case the conducting layers and possibly the semiconductor layer(s) are patterned to provide the required circuitry.

The radiated surface of the solar cell is further coated with one or several layers for providing antireflection surface for the solar cell, and for protecting the solar cell from mechanical, chemical and physical stresses of the environment. Such surfaces may be radiation stabilized glass or plastic products. For example, a glass layer may include self-cleaning TiO₂ coating made by sputtering, Hot-Aerosol-Layering-Operation (nHALO) and by ALD-techniques. The outermost protecting layers may be integrated in the solar cell or they can be separated from the electrical layers.

At the time of filing this patent application there are two main technologies used for producing solar cells. In the first technology silicon or some other semiconducting material is used as a substrate, and further layers are provided on the substrate. So far, this technology is most generally used. However, the production of the silicon substrates as well as forming the further layers with the present manufacturing technology is costly. Also, the weight of large solar cells becomes high, and the large solar cells are relatively sensitive to mechanical strains. These disadvantages prevent an increased use of solar cells.

Another technology for producing solar cells is based on using some other substrate and producing the semiconducting layers as well as other layers as films on the substrate. The substrate may be e.g. glass or plastic. The substrate can be used as the radiated surface of the solar cell, in which case the substrate is made transparent. The solar cells made with this technology have less weight and are not as sensitive to mechanical stresses. However, it has been a problem to achieve sufficient efficiency; usually less than 10% of the energy of light can be converted into electrical energy. One reason for this is the non-homogeneity of the produced layers. Therefore the transparency of the radiated layers may be insufficient. Also, the non-homogeneity of semiconducting layers causes loss of energy.

One problem which causes lack of efficiency is the fact that a junction of semiconducting layer has a specified electric potential threshold, and the energy of photons can only be converted into an amount of energy which corresponds to the potential threshold. The solar light has a wide spectrum of wavelengths and thus the photons have a wide range of energies. If the energy of a photon is lower than the threshold potential of the semiconducting junction, the photon is not converted into electrical energy. On the other hand, if the energy of a photon is higher than the threshold potential of the semiconducting junction, the photon is converted into energy according to the potential threshold, but the energy of the photon above the threshold is converted into heat.

The problem of converting wide spectrum radiation into electrical energy could be solved by providing several successive, transparent semiconductor layers wherein each pair of semiconducting layers provides a junction for converting light to electricity. The semiconductor junctions nearest to the radiated surface have the highest threshold potential and the threshold potential decreases when the radiation enters the following junctions. This way a photon is converted into electricity at a junction which has a threshold potential close to the photon energy, and high efficiency could be achieved. However, it is difficult manufacture several successive, transparent semiconducting layers. If the surfaces of the layers are not sufficiently smooth, light is reflected at each junction layers thus decreasing the efficiency. Also, the non-homogeneity of several semiconductor layers causes loss of electrical energy due to e.g. short circuiting spots in the layer and other uneven distribution of electrical fields.

Further, the production of protecting layers at the radiated surface of a solar cell is also difficult and costly. The processes are slow and need to be made separately from producing the electrical part of the solar cell. Handling the parts in different processes and/or assembly phases may involve a risk of contamination and thus a further loss of efficiency of the final product.

The above mentioned problems become all much more difficult when producing large solar cells as it is necessary to produce layers of large surfaces. The known technologies are suitable for producing cells of small dimensions, e.g. areas of a few cm² at the most, but the quality of surfaces and homogeneity of materials become worse if known technologies would be applied in producing solar cells with layers of large surfaces.

The applicant has investigated possibilities for using laser cold ablation in production of solar cells. In the recent years, considerable development of the laser technology has provided means to produce very high-efficiency laser systems that are based on semi-conductor fibres, thus supporting advance in so called cold ablation methods. Cold ablation is based on forming high energy laser pulses of short duration, such as within picosecond range, and directing the pulses into the surface of a target material. A plume of plasma is thus ablated from the area where the laser beam hits the target. The applications of cold ablation include e.g. coating and machining.

When employing novel cold-ablation, both qualitative and production rate related problems associated with coating, thin film production as well as cutting/grooving/carving etc. has been approached by focusing on increasing laser power and reducing the spot size of the laser beam on the target. However, most of the power increase was consumed to noise. The qualitative and production rate related problems were still remaining although some laser manufacturers resolved the laser power related problem. Representative samples for both coating/thin film as well as cutting/grooving/carving etc. could be produced only with low with repetition rates, narrow scanning widths and with long working time beyond industrial feasibility as such, highlighted especially for large bodies.

Because the energy content of a pulse, the power of the pulse increases in the decrease of the pulse duration, the problem significance increases with the decreasing laser-pulse duration. The problems occur significant even with the nano-second-pulse lasers, although they are not applied as such in cold ablation methods.

The pulse duration decrease further to femto or even to atto-second scale makes the problem almost irresolvable. For example, in a pico-second laser system with a pulse duration of 10-15 ps the pulse energy should be 5 μJ for a 10-30 μm spot, when the total power of the laser is 100 W and the repetition rate 20 MHz. Such a fibre to tolerate such a pulse is not available at the priority date of the current application according to the knowledge of the writer at the very date.

The prior art laser treatment systems most often include optical scanners which are based on vibrating mirrors. Such an optical scanner is disclosed in e.g. document DE10343080. A vibrating mirror oscillates between two determined angles relative to an axis which is parallel to the mirror. When a laser beam is directed to the mirror, it is reflected with an angle which depends on the position of the mirror at that moment. The vibrating mirror thus reflects or “scans” the laser beam into points of a line at the surface of a target material.

An example of a vibrating scanner or “galvano-scanner” is illustrated in FIG. 1a. It has two vibrating mirrors, one of which scans the beam relative to X-axis and another scans the beam relative to orthogonal y-axis.

The production rate is directly proportional to the repetition rate or repetition frequency. On one hand the known mirror-film scanners (galvano-scanners or back and worth wobbling type of scanners), which do their duty cycle in a way characterized by their back and forth movement, the stopping of the mirror at the both ends of the duty cycle is somewhat problematic as well as the accelerating and decelerating related to the turning point and the related momentary stop, which all limit the usability of the mirror as scanner, but especially also to the scanning width. The present coating methods employing galvano-scanners can produce scanning widths at most 10 cm, preferably less. If the production rate were tried to be scaled up, by increasing the repetition rate, the acceleration and deceleration cause either a narrow scanning range, or uneven distribution of the radiation and thus the plasma at the target when radiation hit the target via accelerating and/or decelerating mirror.

Conventionally galvanometric scanners are used to scan a laser beam with a typical maximum speed of about 2-3 m/s, in practice about 1 m/s. If trying to increase the coating/thin film production rate by simply increasing the pulse repetition rate, the present above mentioned known scanners direct the pulses to overlapping spot of the target area already at the low pulse repetition rates in kHz-range, in an uncontrolled way. With repetition rate of 2 MHz even 40-60 successive pulses are overlapping. The overlapping of spots 111 in such a situation are illustrated in FIG. 1b.

At worst, such an approach results in release of particles from the target material, instead of plasma but at least in particle formation into plasma. Once several successive laser pulses are directed into the same location of target surface, the cumulative effect seems to erode the target material unevenly and can lead to heating of the target material, the advantages of cold ablation being thus lost.

The same problems apply to nanosecond range lasers, the problem being naturally even more severe because of the long lasting pulse with high energy. Here, the target material heating occurs always, the target material temperature being elevated to approximately 5000 K. Thus, even one single nanosecond range pulse erodes the target material drastically, with aforesaid problems.

In the known techniques, the target may not only ware out unevenly but may also fragment easily and degrade the plasma quality. Thus, the surface to be coated with such plasma also suffers the detrimental effects of the plasma. The surface may comprise fragments, plasma may be not evenly distributed to form such a coating etc. which are problematic in accuracy demanding application, but may be not problematic, with paint or pigment for instance, provided that the defects keep below the detection limit of the very application.

The present methods ware out the target in a single use so that same target is not available for a further use from the same surface again. The problem has been tackled by utilising only a virgin surface of the target, by moving target material and/or the beam spot accordingly.

In machining or work-related applications the left-overs or the debris comprising some fragments also can make the cut-line uneven and thus inappropriate, as the case could for instance in flow-control drillings. Also the surface could be formed to have a random bumpy appearance caused by the released fragments, which may be not appropriate in manufacturing of solar cells.

In addition, the mirror-film scanners moving back and forth generate inertial forces that load the structure it self, but also to the bearings to which the mirror is attached and/or which cause the mirror movement. Such inertia little by little may loosen the attachment of the mirror, especially if such mirror were working nearly at the extreme range of the possible operational settings, and may lead to roaming of the settings in long time scale, which may be seen from uneven repeatability of the product quality. Because of the stoppings, as well as the direction and the related velocity changes of the movement, such a mirror-film scanner has a very limited scanning width so to be used for ablation and plasma production. The effective duty cycle is relatively short to the whole cycle, although the operation is anyway quite slow. In the point of view of increasing the productivity of a system utilising mirror-film scanners, the plasma making rate is in prerequisite slow, scanning width narrow, operation unstable for long time period scales, but yield also a very high probability to get involved with unwanted particle emission in to the plasma, and consequently to the products that are involved with the plasma via the machinery and/or coating.

The product lifetime of solar cells should also be increased and the maintenance costs should be lowered, sustainable development being a prerequisite. The production of layers especially uniform layer surfaces of large solar cell with one or several of the following properties: excellent optical transparency, chemical and/or wear resistance, scratch-free surface, thermal resistance, coating adhesion, self-cleaning properties and properties derived from resistivity have remained an unsolved problem.

Neither recent high-technological coating methods, nor present coating techniques related to laser ablation either in nanosecond or cold ablation range (pico-, femto-second lasers) can provide any feasible method for industrial scale coating of glass products comprising larger surfaces. The present CVD- and PVD-coating technologies require high-vacuum conditions making the coating process batch wise, thus non-feasible for industrial scale production of solar cells. Moreover, the distance between the material to be coated and the coating material to be ablated is long, typically over 50 cm, making the coating chambers large and vacuum pumping periods time- and energy-consuming. Such high-volume vacuumed chambers are also easily contaminated with coating materials in the coating process itself, requiring continuous and time-consuming cleaning processes.

While trying to increase the production rate in present laser-assisted coating methods, various defects such as short circuiting defect factors, pinholes, increased surface roughness, decreased or disappearing optical transparency, particulates on layer surface, particulates in surface structure affecting corrosion pathways, decreased surface uniformity, decreased adhesion, etc. take place.

Plasma related quality problems are demonstrated in FIGS. 2a and 2b, which indicate plasma generation according to known techniques. A laser pulse 214 hits a target surface 211. As the pulse is a long pulse, the depth h and the beam diameter d are of the same magnitude, as the heat of the pulse 214 also heat the surface at the hit spot area, but also beneath the surface 211 in deeper than the depth h. The structure experiences thermal shock and tensions are building, which while breaking, produce fragments illustrated F. As the plasma may be in the example quite poor in quality, there appears to be also molecules and clusters of them indicate by the small dots 215, as in the relation to the reference by the numeral 215 for the nuclei or clusters of similar structures, as formed from the gases 216 demonstrated in the FIG. 2b. The letter “o”s demonstrate particles that can form and grow from the gases and/or via agglomeration. The released fragments may also grow by condensation and/or agglomeration, which is indicated by the curved arrows from the dots to Fs and from the os to the Fs. Curved arrows indicate also phase transitions from plasma 213 to gas 216 and further to particles 215 and increased particles 217 in size. As the ablation plume in FIG. 2b can comprise fragments F as well as particles built of the vapours and gases, because of the bad plasma production, the plasma is not continuous as plasma region, and thus variation of the quality may be met within a single pulse plume. Because of defects in composition and/or structure beneath the deepness h as well as the resulting variations of the deepness (FIG. 2a), the target surface 211 in FIG. 2b is not any more available for a further ablations, and the target is wasted, although there were some material available.

SUMMARY OF THE INVENTION

An object of the present invention is to provide solar cells, as well as an arrangement and method of their production, wherein the described disadvantages of the prior art are avoided or reduced.

The object of the invention is therefore to provide a technology for producing layers with certain surface by pulsed laser deposition that so that the uniform surface area to be coated comprises at least 0.2 dm².

A second object of this invention is to provide new solar cell products wherein layers are produced by pulsed laser deposition so that the uniform surface area of the layer comprises an area of at least at least 0.2 dm².

A third object of this invention is to solve a problem how to provide available such fine plasma practically from a target to be used in solar cell products, so that the target material do not form into the plasma any particulate fragments either at all, i.e. the plasma is pure plasma, or the fragments, if exist, are rare and at least smaller in size than the ablation depth to which the plasma is generated by ablation from said target.

A fourth object of the invention is to provide at least a new method and/or related means to solve how to provide the uniform surface area of a layer in a solar cell product with the high quality plasma without particulate fragments larger in size than the ablation depth to which the plasma is generated by ablation from said target, i.e. to coat substrates with pure plasma.

A fifth object of this invention is to is to provide a good adhesion of the coating to the uniform surface area of a glass product by said pure plasma, so that wasting the kinetic energy to particulate fragments is suppressed by limiting the existence of the particulate fragments or their size smaller than said ablation depth. Simultaneously, the particulate fragments because of their lacking existence in significant manner, they do not form cool surfaces that could influence on the homogeneity of the plasma plume via nucleation and condensation related phenomena.

A sixth object of the invention is to provide at least a new method and/or related means to solve a problem how to provide a broad scanning width simultaneously with fine plasma quality and broad coating width even for large solar cell bodies in industrial manner.

A seventh object of the invention is to provide at least a new method and/or related means to solve a problem how to provide a high repetition rate to be used to provide industrial scale applications in accordance with the objects of the invention mentioned above.

An eighth object of the invention is to provide at least a new method and/or related means to solve a problem how to provide good quality plasma for coating of uniform glass surfaces to manufacture solar cell products according to the first to seven objects, but still save target material to be used in the coating phases producing same quality coatings/thin films where needed.

A further object of the invention is to use such method and means according previous objects to solve a problem how to cold-work and/or produce layers of a solar cell.

The present invention is based on the surprising discovery that layers for solar cell products comprising large surfaces can be produced with industrial production rates and excellent qualities regarding one or more of technical features such as optical transparency, chemical and/or wear resistance, scratch-free-properties, thermal resistance and/or conductivity, resistivity, coating adhesion, self-cleaning properties, particulate-free coatings, pinhole-free coatings and electronic conductivity by employing ultra short pulsed laser deposition in a manner wherein pulsed laser beam is scanned with a rotating optical scanner comprising at least one mirror for reflecting said laser beam. Moreover, the present method accomplishes the economical use of target materials, because they are ablated in a manner accomplishing the reuse of already subjected material with retained high coating results. The present invention further accomplishes the producing of product layers in low vacuum conditions with simultaneously high coating properties. Moreover, the required coating chamber volumes are dramatically smaller than in competing methods. Such features decrease dramatically the overall equipment cost and increase the coating production rate. In many preferable cases, the coating equipment can be fitted into production-line in online manner.

More specifically, the object of the invention is achieved by providing a method for producing by laser ablation at least one layer having a surface and to be used as part of a solar cell, which is characterized in that the surface area to be produced comprises at least an area 0.2 dm² and the coating is performed by employing ultra short pulsed laser deposition wherein pulsed laser beam is scanned with a rotating optical scanner comprising at least one mirror for reflecting said laser beam.

The invention also relates to a solar cell comprising at least one layer with a surface, produced by laser ablation, which is characterized in that the uniform surface area to be produced comprises at least an area 0.2 dm² and the layer has been produced by employing ultra short pulsed laser deposition wherein pulsed laser beam is scanned with a rotating optical scanner comprising at least one mirror for reflecting said laser beam.

Some embodiments of the invention are described in dependent claims.

In this patent application term “light” means any electromagnetic radiation which can be used for cold ablation and “laser” means light which is coherent or a light source producing such light. “Light or “laser” is thus not restricted in any way to the visible part of the light spectrum.

In this patent application term “ultra short pulse laser deposition” means that a certain point at the target surface is radiated with a laser beam for a time period of less than 1 ns, preferably less than 100 ps at a time. Such an exposure may be repeated at the same location of the target.

In this patent application term “coating” means forming material layer of any thickness on a substrate. Coating thus may also mean producing thin films with a thickness of e.g. <1 μm.

In this patent application term “surface” may mean surface of a layer, coating and/or, wherein the surface may be an outer surface or it may form an interface with other layer/coating/substrate. The surface may also be a surface of a half-finished product, which may be further processed to achieve a final product.

BRIEF DESCRIPTION OF THE DRAWINGS

The described and other advantages of the invention will become apparent from the following detailed description and by referring to the drawings where:

FIG. 1 illustrates an exemplary galvano-scanner set-up employed in state of the art cold ablation coating/thin-film production and in machining and other work-related applications.

FIG. 1b illustrates the situation wherein prior art galvanometric scanner is employed in scanning laser beam resulting in heavy overlapping of pulses with repetition rate of 2 Mhz.

FIG. 2a illustrates plasma-related problems of known techniques.

FIG. 2b illustrates further plasma-related problems of known techniques.

FIG. 3 illustrates exemplary layers produced for a solar cell.

FIG. 4 illustrates an exemplary arrangement according to the invention for producing a layer for a solar cell using pulsed laser technology.

FIG. 5 illustrates an exemplary arrangement according to the invention for producing several layers of a solar cell using pulsed laser technology.

FIG. 6a illustrates one possible turbine scanner mirror employed in a method according to the invention,

FIG. 6b illustrates the movement of the ablating beam achieved by each mirror in the example of FIG. 6a.

FIG. 7 illustrates beam guidance through one possible rotating scanner to be employed according to the invention.

FIG. 8a illustrates beam guidance through another possible rotating scanner to be employed according to the invention.

FIG. 8b illustrates beam guidance through a further possible rotating scanner to be employed according to the invention.

FIG. 10a illustrates an embodiment according to the invention, wherein target material ablated by scanning the laser beam with rotating scanner (turbine scanner).

FIG. 10b illustrates an exemplary part of target material of FIG. 10a.

FIG. 10c illustrates an exemplary ablated spot of target material of FIG. 110b.

FIG. 11 illustrates an exemplary way according to the invention to scan and ablate target material with a rotating scanner.

DETAILED DESCRIPTION

FIGS. 1a, 1b, 2a and 2b where already described above in the prior art description.

FIG. 3 illustrates exemplary layers of a solar cell, which is based on film layer technology. The substrate 360 may be e.g. glass or plastic material. At the radiated surface of the solar cell there is a antireflection layer 362. There may also be other or additional layers for keeping the outer surface clean and protected from environmental stresses. At the inner surface of the substrate 360 there is an electrically conducting layer 364 which may be patterned according to the circuit layout and partitioning of the solar cell. The conducting layer is preferably transparent and/or the conductive wiring is made of narrow leads which cover only a small part of the surface area. Next, above the conductive layer, there is one or several semiconducting layers 366. Finally, there is another conductive layer 368 for providing wiring of a second electrical potential of the solar sell. The second conductive layer need not be transparent if there are no further semiconducting layers behind the conducting layer. There may also be an additional, protecting layer at the surface of the second conductive layer.

If a solar cell is produced with a semiconducting substrate, there exists similar layers in similar order, but the production is implemented by starting with a semiconducting substrate and producing other layers on that substrate.

FIG. 4 illustrates an exemplary system for treating material with laser ablation. A laser beam formed by a laser source 44 and scanned with a rotating optical scanner 10 towards the target. The target 47 has a form of a band which is spooled from a feed roll 48 into a discharge roll 46. The target is supported with a support plate 51 which has an opening 52 at the location of ablation. However, the target may alternatively be other than band, such as a rotating cylinder of target material. When the laser beam 49 received from the scanner hits the target, material is ablated, and a plasma plume is provided. A substrate 50 is provided into the plasma plume. The substrate will thus be coated with a layer of target material. If a layer is to be machined after the deposition, this can be made with a laser beam.

It is also to possible to provide the laser ablation with many other alternative structures and arrangements. For example, it is naturally possible to provide the deposition from under or above the substrate or both. It is also possible to use target material which is provided on a transparent sheet. In such an arrangement it is possible to provide the target material very close to the substrate and to provide the laser beam to the target material through the transparent part of the sheet. If the target material is a thin film at the sheet, it will ablate towards the substrate. The target sheet can be first produced by ablating the target material on a transparent sheet.

FIG. 5 illustrates an exemplary production line arrangement for producing layers for a solar cell. The arrangement includes five laser processing units 571-575 within a same processing chamber 510. Above the processing unit there is a conveyor 591 for transferring substrates 581-585 along the line. Each processing unit provides a certain process for the substrate. The processing units may produce layers or they may provide laser machining of the substrate or produced layers. Naturally, there may also be other types of processing units within the production line. It is an important advantage of the invention that layers of different materials can be deposited within a same chamber on the same production line. It is even possible to provide possibly required laser patterning. When all or most of the layers are produced in the same chamber, the risk of contamination or other defects due to handling of semi-finished products is minimal.

Next, the physical basis and structure of suitable rotating scanners is described. According to the invention there is provided a method for providing a layer for a solar cell with a certain surface by laser ablation in which method the surface area to be coated comprises at least 0.2 dm² and the depositing is carried by employing ultra short pulsed laser deposition wherein pulsed laser beam is scanned with a rotating optical scanner comprising at least one mirror for reflecting said laser beam.

Ultra Short Laser Pulsed Deposition is often shortened USPLD. Said deposition is also called cold ablation, in which one of the characteristic features is that opposite for example to competing nanosecond lasers, practically no heat transfer takes place from the exposed target area to the surroundings of this area, the laser pulse energies being still enough to exceed ablation threshold of target material. The pulse lengths are typically under 50 ps, such as 5-30 ps. i.e. ultra short, the phenomena of cold ablation being reached with pico-second but also femto-second and atto-second pulsed lasers. The material evaporated from the target by laser ablation is deposited onto a substrate that can be held near room temperature. Still, the plasma temperature reaches 1,000,000 K on exposed target area. The plasma speed is superior, gaining 100,000 m/s and thus, leading to better adhesion of coating/thin-film produced. In a more preferred embodiment of the invention, said uniform surface area comprises at least 0.5 dm². In a still more preferred embodiment of the invention, said uniform surface area comprises at least 1.0 dm². The invention accomplishes easily also the coating of products comprising uniform coated surface areas larger than 0.5 m², such as 1 m² and over. The process is especially beneficial for coating large surfaces of layers for solar cells with high quality plasma.

In industrial applications, it is important to achieve high efficiency of laser treatment. In cold ablation, the intensity of laser pulses must exceed a predetermined threshold value in order to facilitate the cold ablation phenomenon. This threshold value depends on the target material. In order to achieve high treatment efficiency and thus, industrial productivity, the repetition rate of the pulses should be high, such as 1 MHz, preferably over 2 MHz and more preferably over 5 MHz. As mentioned earlier, it is advantageous not to direct several pulses into same location of the target surface because this causes a cumulating effect in the target material, with particle deposition leading to bad quality plasma and thus, bad quality coatings and thin-films, undesirable eroding of the target material, possible target material heating etc. Therefore, to achieve a high efficiency of treatment, it is also necessary to have a high scanning speed of the laser beam. According to the invention, the velocity of the beam at the surface of the target should generally be more than 10 m/s to achieve efficient processing, and preferably more than 50 m/s and more preferably more than 100 m/s, even such speeds as 2000 m/s.

FIG. 6a illustrates an example of a rotating turbine scanner, which can be used in implementing the invention. According to this embodiment, rotating optical scanner comprises at least three mirrors for reflecting laser beam. In one embodiment of the invention, in the coating method employs a polygonal prism illustrated in FIG. 5. Here, a polygonal prism has faces 21, 22, 23, 24, 25, 26, 27 and 28. Arrow 20 indicates that the prism can be rotated around its axis 19, which is the symmetry axis of the prism. When the faces of the prism of the FIG. 6a are mirror faces, advantageously oblique in order to achieve scanning line, arranged such that each face in its turn will change, by means of reflection, the direction of radiation incident on the mirror surface as the prism is rotated around its axis, the prism is applicable in the method according to an embodiment of the invention, in its radiation transmission line, as part of a rotating scanner, i.e. turbine scanner. FIG. 6a shows 8 faces, but there may be considerably more faces than that, even dozens or hundreds of them. FIG. 6a also shows that the mirrors are at the same oblique angle to the axis, but especially in an embodiment including several mirrors, the said angle may vary in steps so that, by means of stepping within a certain range, a certain stepped shift on the work spot is achieved on the target, illustrated in FIG. 6b. The different embodiments of invention are not to be limited into various turbine scanner mirror arrangements regarding for example the size, shape and number of laser beam reflecting mirrors.

The structure of the turbine scanner, FIG. 6a, includes at least 2 mirrors, preferably more than 6 mirrors, e.g. 8 mirrors (21 to 28) positioned symmetrically around the central axis 19. As the prism 21 in the turbine scanner rotates 20 around the central axis 19, the mirrors direct the radiation, a laser beam, for instance, reflected from spot 29, accurately onto the line-shaped area, always starting from one and the same direction (FIG. 6b). The mirror structure of the turbine scanner may be non-tilted (FIG. 7) or tilted at a desired angle, e.g. FIGS. 8a and 8b. The size and proportions of the turbine scanner can be freely chosen. In one advantageous embodiment of the coating method it has a perimeter of 30 cm, diameter of 12 cm, and a height of 5 cm.

In an embodiment of the invention it is advantageous that the mirrors 21 to 28 of the turbine scanner are preferably positioned at oblique angles to the central axis 19, because then the laser beam is easily conducted into the scanner system.

In a turbine scanner according to be employed according to an embodiment of the invention (FIG. 6a) the mirrors 21 to 28 can deviate from each other in such a manner that during one round of rotational movement there are scanned as many line-shaped areas (FIG. 6b) 29 as there are mirrors 21 to 28.

According to one embodiment of the invention, rotating optical is here meant scanners comprising at least one mirror for reflecting laser beam. Such a scanner and its applications are described in patent application F120065867. FIG. 9 illustrates a scanner 910 with one rotating mirror. The mirror 914 is arranged to rotate around the axis of rotation 916. FIG. 9 also shows the side view and the end view of the mirror. The mirror has a shape of a cylinder, which is slightly tilted in relation to the axis of rotation 916. The mirror is shown as a tilted cylinder in order to better visualize the form of the mirror, and the ends of the mirror are therefore oblique. However, it would also be possible to have edges which are perpendicular to the axis of rotation. The optical scanner has an axle at the axis of rotation, in which the mirror is connected. The mirror may be connected to the rotating axle with e.g. end plates or spokes (not shown in the Figure).

FIG. 10a demonstrates a target material ablated with pico-second-range pulsed laser employing rotating scanner with speed accomplishing the ablation of target material with slight overlapping of adjacent pulses, avoiding the problems associated with prior art galvano-scanners. FIG. 10b shows enlarged picture of one part of the ablated material, clearly demonstrating the smooth and controlled ablation of material on both x- and y-axis and thus, generation of high quality, particle-free plasma and further, high quality thin-films and coatings. FIG. 10c demonstrates one example of possible x- and y-dimensions of one single ablation spot achieved by one or few pulses. Here, it can be clearly seen, that the invention accomplishes the ablation of material in a manner wherein the width of the ablated spot is always much bigger than the depth of the ablated spot area. Theoretically, the possible particles (if they would be generated) could now have a maximum size of the spot depth. The rotating scanner now accomplishes the production of good quality, particle free plasma with great production rate, with simultaneously large scanning width, especially beneficial for substrates comprising large surface areas to be coated. Furthermore, the FIGS. 10a, 10b and 10c clearly demonstrate that opposite to present techniques, the already ablated target material area can be ablated for new generation of high class plasma—reducing thus radically the overall coating/thin-film producing cost.

FIG. 11 demonstrates an example wherein coating is carried out by employing a pico-second USPLD-laser and scanning the laser pulses with turbine scanner. Here, the scanning speed is 30 m/s, the laser spot-width being 30 μm. In this example, there is ⅓ overlapping between the adjacent pulses.

Next some materials are described which are suitable as target materials for providing layers of the solar cell. The layer of conductive transparent material can be made of e.g. indium tin oxide, aluminum doped zinc oxide, tin oxide or fluorine-doped tin oxide. The layer of conductive non-transparent material can be made of e.g. aluminum, copper or silver. The layer of semiconducting material can be made of e.g. silicon, germanium indium tin oxide, aluminum doped zinc oxide, tin oxide or fluorine-doped tin oxide. The layer of antireflective coating can be made of e.g. of silicon nitride or titanium oxide. However, this are just some examples of commonly used materials. Next, some further alternatives are discussed in more detail.

Advantageous metal oxides include for example aluminum oxide and its different composites such as aluminum titan oxide (ATO). Due to its resistivity, high-optical transparencies possessing high-quality indium tin oxide (ITO) is especially preferred in applications wherein the coating can be employed to warm-up the coated surface. It can also be employed in solar-control Yttrium stabilized zirconium oxide is another example of different oxides possessing both excellent optical, wear-resistant properties.

Some further metals can also be applied in solar cell applications. Here, the optical properties of metal-derived thin-films are somewhat different from those of bulk metals. In ultrathin films (<100 Å thick) variations make the concept of optical constants problematic, the quality and surface roughness of the coating (thin film) being thus critical technical features. Such coatings can easily be produced with the method of present invention.

Dielectric materials employed in present applications include fluorides (e.g. MgF₂, CeF₃), oxides (e.g. Al₂O₃, TiO₂, SiO₂), sulfides (e.g. ZnS, CdS) and assorted compounds such as ZnSe and ZnTe. An essential common feature of dielectric optical materials in their very low absorption (α<10³/cm) in some relevant portion of the spectrum; in this region they are essentially transparent (e.g. fluorides and oxides in the visible and infrared, chalcogenides in the infrared). Dielectric coatings can be advantageously produced with the method of present invention.

Transparent conducting films may consist either of very thin metals or semiconducting oxides and/ and most presently even nitrides such as indium gallium nitride in front electrodes for solar cells.

Metals that have conventionally been employed be as transparent conductors include Au, Pt, Rh, Ag, Cu, Fe and Ni. Simultaneous optimization of conductivity and transparency presents a considerable challenge in film deposition. At one extreme are discontinuous islands of considerable transparency but high resistivity; at the other are films that coalesce early and are continuous, possessing high conductivity but low transparency. For these reasons, the semi-conducting oxides such as SnO₂, In₂O₃, CdO, and, more commonly, their alloys (e.g. ITO), doped In₂O₃ (with Sn, Sb) and doped SnO₂ (with F, Cl, etc.) are used.

The metal oxide coatings can be produced by either ablating metal or metals in active oxygen atmosphere or by ablating oxide-materials. Even in latter possibility, it is possible to enhance the coating quality and/or production rate by conducting the ablation in reactive oxygen. When producing nitrides it is according to the invention possible to use nitrogen atmosphere or liquid ammonia in order to enhance the coating quality. A representative example of invention is production of carbon nitride (C₃N₄ films).

According another embodiment of the invention, said uniform surface area of solar cell layer is produced with carbon material comprising over 90 atomic-% of carbon, with more than 70% of sp³-bonding. Such materials include for example amorphous diamond, nano-crystalline diamond or even pseudo-monocrystalline diamond. Various diamond coatings give the glass product excellent tribological, wear- and scratch-free properties but increase also the heat-conductivity and -resistance. Diamond-coatings on glass can be used with special preference in solar cells, if of high quality, i.e. crystalline form.

In a still another embodiment of the invention, said uniform surface area of may be produced of material comprising carbon, nitrogen and/or boron in different ratios. Such materials include boron carbon nitride, carbon nitride (both C₂N₂ and C₃N₄), boron nitride, boron carbide or phases of different hybridizations of B—N, B—C and C—N phases. Said materials are diamond-like materials having low densities, are extremely wear-resistant, and are generally chemically inert. For example carbon nitrides can be employed to protect glass products against corrosive conditions, as coatings in solar cells.

According to one embodiment of invention, the outer surface of the solar cell product is coated with only one single coating. According to another embodiment of the invention, said uniform surface of the solar cell is coated with multilayered coating. Several coatings can be produced in for different reasons. One reason might be to enhance the adhesion of certain coatings to glass product surfaced by manufacturing a first set of coating having better adhesion to glass surface and possessing such properties that the following coating layer has better adhesion to said layer than to glass surface itself. Additionally, the multilayered coating can possess several functions not achievable without said structure. The present invention accomplishes the production of several coatings in one single coating chamber or in the adjacent chambers.

The present invention further accomplishes the production of composite layers/coatings to solar cells ablating simultaneously one composite material target or two or more target materials comprising one or more substances.

A suitable thickness of an ablated layer is e.g. between 20 nm and 20 μm, preferably between 100 nm and 5 μm. The coating thicknesses must not be limited to those, because the present invention accomplishes the preparation of molecular scale coatings on the other hand, very thick coatings such as 100 μm and over, on the other hand.

According to the invention there may also provided a solar cell product comprising a certain surface being coated by laser ablation wherein the coated uniform surface area comprises at least 0.2 dm² and that the coating has been carried by employing ultra short pulsed laser deposition wherein pulsed laser beam is scanned with a rotating optical scanner comprising at least one mirror for reflecting said laser beam. The benefits received with these products are described in more detail in the previous description of the method.

In a more preferred embodiment of the invention said uniform surface area comprises at least 0.5 dm². In a still more preferable embodiment of the invention said uniform surface area comprises at least 1.0 dm². The invention accomplishes easily also the products comprising uniform coated surface areas larger than 0.5 m², such as 1 m² and over.

According to one embodiment of the invention the average surface roughness of produced coating on said uniform surface area is less than 100 nm as scanned from an area of 100 μm² with Atomic Force Microscope (AFM).

According to another embodiment of the invention the optical transmission of produced coating on said uniform surface area is no less than 88%, preferably no less than 90% and most preferably no less than 92%. In some cases the optical transparency can exceed 98%.

According to still another embodiment of the invention said uniform surface area is coated in a manner wherein the first 50% of said coating on said uniform surface area does not contain any particles having a diameter exceeding 1000 nm, preferably 100 nm and most preferably 30 nm.

According to one embodiment of the invention said layer comprises metal, metal oxide, metal nitride, metal carbide or mixtures of these. The possible metals were described earlier in description of now invented coating method.

According to another embodiment of the invention said uniform surface area of glass product is coated with carbon material comprising over 90 atomic-% of carbon, with more than 70% of sp³-bonding. The possible carbon materials were described earlier in description of now invented coating method.

According to still another embodiment of the invention said uniform surface area comprises carbon, nitrogen and/or boron in different ratios. Such materials were described earlier in description of now invented coating method.

According to still another embodiment of the invention said uniform surface area the product is coated with organic polymer material. Such materials were described earlier in more detail in description of now invented coating method.

According to one preferred embodiment of the invention the thickness of said coating on uniform surface of glass product is between 20 nm and 20 μm, preferably between 100 nm and 5 μm. The invention accomplishes also coated glass products comprising one or several atomic layer coatings and thick coatings such as exceeding 100 μm, for example 1 mm.

In this patent specification the structure of the other various components of a laser ablation apparatus is not described in more detail as they can be implemented using the description above and the general knowledge of a person skilled in the art.

Above, only some embodiments of the solution according to the invention have been described. The principle according to the invention can naturally be modified within the frame of the scope defined by the claims, for example, by modification of the details of the implementation and ranges of use.

For example, only a few structures of solar cells have been discussed as examples. There are many other types of other alternative structures, wherein the structure comprises one or several layers of different materials, commonly semiconducting, conductive, insulating and transparent materials. In is naturally possible to use to apply the present invention also in such other types of structures of solar cells.

Claims

1-41. (canceled)

42. A method for producing by laser ablation at least one layer having a surface and to be used as part of a solar cell, characterized in that the surface area to be produced comprises at least an area 0.2 dm2 and the coating is performed by employing ultra short pulsed laser deposition wherein pulsed laser beam is scanned with a rotating optical scanner comprising at least one mirror for reflecting said laser beam.

43. A method according to claim 42, characterized in that said surface area is a uniform surface area.

44. A method according to claim 42, characterized in that said surface area comprises at least an area 0.5 dm2, preferably at least an area 1.0 dm2.

45. A method according to claim 42, characterized in that the employed pulse frequency of said laser deposition is at least 1 MHz.

46. A method according to claim 42, characterized in that the surface of the semiconductor or conductive layer does not comprise short circuiting defect factors.

47. A method according to claim 42, characterized in that the average surface roughness of produced layer on said uniform surface area is less than 100 nm as scanned from an area of 100 μm2 with Atomic Force Microscope (AFM).

48. A method according to claim 42, characterized in that the optical transmission of a produced layer on said uniform surface area is no less than 88%, preferably no less than 90% and most preferably no less than 92%.

49. A method according to claim 42, characterized in that a layer of conductive transparent material is made of indium tin oxide, aluminum doped zinc oxide, tin oxide or fluorine-doped tin oxide.

50. A method according to claim 42, characterized in that a layer of conductive non-transparent material is made of aluminum or copper.

51. A method according to claim 42, characterized in that a layer of semiconducting material is made of silicon, germanium indium tin oxide, aluminum doped zinc oxide, tin oxide or fluorine-doped tin oxide.

52. A method according to claim 42, characterized in that a layer of antireflective coating is made of silicon nitride or titanium oxide.

53. A method according to claim 42, characterized in that the layer comprises at least one of following materials or a mixture of these:

at least 80% metal oxide or composition thereof; or

carbon, nitrogen and/or boron; or

carbon material comprising over 90 atomic-% of carbon, with more than 70% of sp3-bonding.

54. A method according to claim 42, characterized in that the outer surface of said solar cell is coated with multilayered coating.

55. A method according to claim 42, characterized in that the thickness of the layer is between 20 nm and 20 μm, preferably between 100 nm and 5 μm.

56. A solar cell comprising at least one layer with a surface, produced by laser ablation, characterized in that the surface area to be produced comprises at least an area 0.2 dm2 and the layer has been produced by employing ultra short pulsed laser deposition wherein pulsed laser beam is scanned with a rotating optical scanner comprising at least one mirror for reflecting said laser beam.

57. A solar cell according to claim 56, characterized in that said surface area is a uniform surface area.

58. A solar cell according to claim 56, characterized in that said surface area comprises at least an area 0.5 dm2, preferably at least an area 1.0 dm2.

59. A solar cell according to claim 56, characterized in that the average surface roughness of produced coating on said uniform surface area is less than 100 nm as scanned from an area of 100 μm2 with Atomic Force Microscope (AFM).

60. A solar cell according to claim 56, characterized in that the surface does not comprise short circuiting defect factors.

61. A solar cell according to claim 56, characterized in that the optical transmission of produced coating on said uniform surface area is no less than 88%, preferably no less than 90% and most preferably no less than 92%.

62. A solar cell according to claim 56, characterized in that said surface area is coated in a manner wherein the first 50% of said coating on said uniform surface area does not contain any particles having a diameter exceeding 1000 nm, preferably 100 nm and most preferably 30 nm.

63. A solar cell according to claim 56, characterized in that a layer of conductive transparent material is made of indium tin oxide, aluminum doped zinc oxide, tin oxide or fluorine-doped tin oxide.

64. A solar cell according to claim 56, characterized in that a layer of conductive non-transparent material comprises aluminum, copper or silver.

65. A solar cell according to claim 56, characterized in that a layer of semiconducting material comprises silicon, germanium indium tin oxide, aluminum doped zinc oxide, tin oxide or fluorine-doped tin oxide.

66. A solar cell according to claim 56, characterized in that a layer of antireflective coating comprises silicon nitride or titanium oxide.

67. A solar cell according to claim 56, characterized in that said layer comprises at least one of following materials or a mixture of these:

metal, metal oxide, metal nitride, and/or metal carbide; or

carbon, nitrogen and/or boron; or

carbon material comprising over 90 atomic-% of carbon, with more than 70% of sp3-bonding.

68. A solar cell according to claim 56, characterized in that the outer surface of the solar cell has a multilayered coating.

69. A solar cell according to claim 56, characterized in that the thickness of said layer for a solar cell is between 20 nm and 20 μm, preferably between 100 nm and 5 μm.

70. An arrangement for producing at least one part of a solar cell, the apparatus comprising means for producing at least one layer with a surface by laser ablation, characterized in that the surface area to be produced comprises at least an area 0.2 dm2 and the arrangement comprises means for providing the layer by employing ultra short pulsed laser deposition wherein the arrangement comprises a rotating optical scanner for scanning pulsed laser beam, the rotating scanner comprising at least one mirror for reflecting said laser beam.

71. An arrangement according to claim 70, characterized in that said surface area is a uniform surface area.

72. An arrangement according to claim 70, characterized in that the arrangement comprises means for producing at least two layers for a same solar cell within a same chamber.

73. An arrangement according to claim 70, characterized in that the arrangement comprises means for machining layers or substrate of a same solar cell within a same chamber.