GB2184601A - A process for producing a solar cell arrangement - Google Patents

Abstract

On a substrate 1 a first electrode layer 2 is firstly deposited over a large area and excavated in regions 3. In considerable simplification of conventional processes, a photosensitive semiconductor layer 5 as well as a second electrode layer 6 are then directly successively applied over the same large area by vacuum deposition. Only after this is the excavation of these layers in regions 7 and 9 as well as the final series wiring by appropriate contact elements 10 effected. The second electrode layer 6 is advantageously excavated by etching, the semiconductor layer 5 by local application of ultrasonics. <IMAGE>

Description

SPECIFICATION A process for producing a Solar Cell Arrangement This invention relates to a process for producing a solar cell arrangement in series connection and integrated thin layer technology.

Such a process is known from German Patent Specification DE-A1-32 742. In a first step of this known process, a transparent metal layer serving as a first electrode layer is deposited by evaporation over a large area of a glass substrate.

Then this first electrode layer is excavated in specific regions, preferably by scratching, in order to produce trenches reaching right down to the substrate surface. This process step predetermines the eventual structuring into a sequence of individual solar cells lying side-by-side. A continuous semiconductor layer is then deposited in a similarwidespread manner onto the now separated zones of the first electrode layer. In this respect, the semiconductor material is preferably amorphous silicon, which has, for example, a pinlayer structure. The large-area deposition of the semiconductor layer is effected in a quasi-vacuum with the aid of a glow-discharge process, for example, from a silane-containing gas atmosphere, as for instance in U.S. Patent Specification No. 4064 521.Then, separate contact elements, which are later supposed to serve for series connection of the individual solar cells, are applied to the continuous semiconductor layer, which is internally so structured that incident electromagnetic energy, more especially in the form of light, is converted into electrical charge. These contact elements, consisting, for example, of aluminium, are deposited in a strip-shaped manner by vaporization with the aid of masking processes or in a photolithographical way above the trenches which have arisen because of the regional removal of the first electrode layer. In a subsequent process step a continuous second electrode layer, consisting for example of indium tin oxide (ITO), is deposited by evaporation over the semiconductor layer with the contact element strips present thereon. This generally also happens in a vacuum.In the solar cell arrangement thus far constructed the individual solar cells are still electrically short-circuited by the continuous second electrode layer over their upper side surface. In order to abolish this short-circuit, the second electrode layer as well as the semiconductor layer beside next to the contact element strips is scratched away up to the surface of the first electrode layer, for example in the same way as in the case of the first electrode layer using a laser beam. The individual solar cells are thereby electrically insulated from one another. In order to bring about series connection of the solar cells one with the other, the arrangement is then subjected to heat treatment so that the metallic contact elements melt and spread through the semiconductor layer so far as the surface of the respective first electrode layer of the neighbouring solar cell.In this way electrical contacts between the first and second electrode layer of respective neighbouring solar cells are established.

This known production process proves, as a whole, to be relatively complex. Apart from the first electrode layer, the two further layers, namely the semiconductor layer as well as the second electrode layer, are deposited over a large area by a vacuum process, but these two process steps are interrupted by an intermediate process step wherein the stripshaped metallic contact elements are applied. This takes place using a masking process or by lithographical means. These two process variants are relatively complex and necessitate an interruption of the vacuum process. Furthermore, the establishment of the series connection of the individual solar cells by heat treatment is relatively uncertain.In this respect uniform melting and spreading of the metallic contact elements through the semiconductor layer cannot be adequately controlled so the contacts which are made are possibly non-uniform.

The object of the invention is to make available a simplified process of solar cell production wherein series connection of the individual solar cells is effected in a more reliable and uniform manner than hitherto.

In accordance with the invention, this object is achieved by a process for producing a solar cell arrangement in series connection and integrated thin layer technology, in which first of all a first electrode layer is applied over a large area of a substrate and then excavated in specific regions, then a semiconductor layer suitably structured for the conversion of incident electromagnetic radiation into electric energy is applied by vacuum deposition from the gas phase, over a similar large area, and in a further process cycle a second electrode layer is deposited over a similar large area and separate contact elemets serving for series connection of the individual solar cells are applied, characterised in that the semiconductor layer and the second electrode layer are applied directly in succession by vacuum deposition, then the second electrode layer is removed in separate regions approximately following the pattern of the excavated regions of the first electrode layer, those regions of the semiconductor layer which are thus exposed are at least partially excavated, and finally the separate contact elements are applied in the layer gaps afforded by the removed and excavated regions of the second electrode layer and the semiconductor layer to provide electrical contact exclusively between the first and second electrode layers of respective neighbouring solar cells.

The particular advantage of the process in accordance with the invention is that the vacuum processes necessary for the application of the semiconductor layer as well as of the second electrode layer directly follow one another. The substrate with the excavated first electrode layer can thus be channeled directly successively through two neighbouring vacuum chambers, in the first of which the semiconductor layer and in the second of which the second electrode layer is applied over a similar large area. In contrast to the previously known process, the semi-finished solar cell arrangement after application of the semiconductor layer does not have to be removed from the vacuum in order, in a complex process step, to apply seperate contact elements.Thus it is not necessary to fumigate the semiconductor surface prior to the depositing by evaporation of the second electrode layer, which takes place in a further vacuum process. Moreover the danger of damaging the semiconductor layer in the course of application of the contact elements does not exist.

Furthermore, as a result of the further process steps provided in accordance with the invention the series connection takes place by providing the contact elements in a reliable and easily controllable manner.

If the light is incident from the substrate side the second electrode layer is advantageously a metal layer which is excavated in specific separate regions by etching. With this means of removal, the semiconductor layer lying thereunder is not damaged.

The surface regions of the semiconductor layer exposed by the aforesaid etching can then advantageously be excavated, at least partially, by localised use of ultrasonics, and also by etching if necessary. With the aid of an ultrasonic probe it is possible to excavate the semiconductor manner locally in A well planned manner without damaging neighbouring regions of this layer or the first electrode layer lying therebelow, which, in the event of light incidence from the substrate side, is advantageously a transparent conductive oxide. The second electrode layer and the semiconductor layer which are applied directly successively and both over the same large area can also be jointly excavated, for example by etching.

An exemplified embodiment of the invention will be described in more detail hereinunderwith reference to the figures which represent successive stages in the process. Schematically and respectively in cross-section: Fig. 1 is a substrate with a first electrode layer; Fig. 2 is the arrangement in accordance with Fig. 1 after excavation of specific regions of the first electrode layer; Fig. 3 is the arrangement in accordance with Fig. 2 after application of a semiconductor layer over a large area; Fig. 4 is the arrangement in accordance with Fig. 3 after application of a second electrode layer over a similar large area; Fig. 5 is the arrangement in accordance with Fig. 4 after removal of specific regions of the second electrode layer; Fig. 6 is the arrangement in accordance with Fig. 5 after excavation of separate specific regions of the semiconductor layer;; and Fig. 7 is the arrangement in accordance with Fig. 6 after application of separate contact elements.

The process steps shown in the figures relate to a solar cell arrangement in which the light is incident from the substrate side. Therefore a transparent substrate 1, for example glass, is used. To begin with, in accordance with Fig. 1, a continuous first electrode layer 2 is applied over a large area of this substrate. The electrode material may, for example, be a transparent conductive oxide (TCO), for instance indium oxide, tin oxide or indium oxide (ITO). This first electrode layer is applied in the acccustomed manner, for example by sputtering or deposition by vaporization. Subsequently, in accordance with Fig. 2, the first electrode layer 2 is excavated at specific regions 3. As a result of this excavation, the splitting up of the surface into individual solar cells 4, 8 is predetermined.In the exemplified embodiment the regions 3 extend in a trench-shaped manner perpendicular to the drawing plane. Photolithography, laser beams or other partinent methods can be used for this excavation of the first electrode layer 2. In particular, the use of electroerosion wherein an appropriately shaped probe, which has a potential difference relative to the elelctrode layer, is conducted across the latter, proves to be advantageous. In this respect, the electrode layer can be covered with an at least weakly conductive liquid, so that the layer in its entirety is held at the same potential. As well as eiectroerosion and laser scratching, other pertinent processes are also usable for structuring the first electrode layer consisting of a transparent conductive oxide.

Subsequently, in accordance with the invention, two immediately consecutive vacuum process steps are carried out. In accordance with Fig. 3, first of all a continuous semiconductor layer 5 is applied over a large area. This may consist of an amorphous silicon layer with pin-layer structure, but other materials customary in the thin-layer solar cell technique are also usable, for instance amorphous germanium, gallium arsenide or cadmium sulphide/ copper sulphide. The semiconductor layer 5 should, in any case, be so constructed by pin-transition or barrier-layer zones that conversion of incident electromagnetic energy, preferably in the form of light, into electrical energy, i.e. separate charges, is possible.

In the case of an amorphous silicon layer as semiconductor layer 5, this can be deposited in the customary manner by glow discharge from a gas atmosphere which contains a silicon-containing compound, for instance silane or a halogencontaining silane, as well as possibly hydrogen or carbon constituents. Of course, during this deposition process, doping elements can be admixed in the necessary manner with the gas atmosphere.

As an alternative to glow discharge in a quasivacuum, other vacuum processes are permissible for the deposition of the semiconductor layer 5, for example those using thermal or photochemical decomposition of silicon-containing molecules in the gas phase, or even sputtering.

In accordance with Fig. 4 in a second, immediately subsequent, vacuum process step a continuous second electrode layer is applied over a large area of the semiconductor layer 5. In the event of light incidence from the substrate side, the second electrode material can be a thin metal layer, for example of aluminium, nickel, silver, gold or titanium, of individual elements or mixtures, for instance aluminium and silicon. This second electrode layer 6 is advantageously deposited by evaporation in a vacuum or else applied by sputtering.

In order to cancel the short-circuit existing through the as yet uninterrupted second electrode layer 6 at the surface of all the individual solar cells, this electrode layer 6 is now removed in specific regions 7. The position of these regions 7 is to some extent predetermined by the position of the regions 3, and in the exemplified embodiment in accordance with Fig. 5 a laterally offset parallel position is chosen. The separate regions 7 in which the semiconductor layer 5 lying thereunder is exposed thus follow approximately the pattern of the excavated regions 3 of the first electrode layer 2.

The second electrode layer 6, consisting of metal, is removed in these predetermined regions 7 preferably by etching. By selecting a suitable etching agent, for example a mixture of phosphoric acid (H3PO4) and nitric acid (N HO3) in the case of a metal layer 5 thereunder, here an amorphous silicon layer, is not damaged. As an alternative to etching, the metal layer 6 could be removed in the regions 7 by laser scratching. If circumstances permit, however, an etching process is less complex with regard to apparatus required and with such a process a clean excavation or removal of the second electrode layer 6 is possible. In order to remove residues from the surface of the solar cell arrangement, this is subsequently rinsed.

In a following process step in accordance with Fig.

6 the semiconductor layer 5 which is exposed in the regions 7 is partially removed, namely in the regions 9. Here a process which enables a particularly accurate excavation of the semiconductor layer 5 is the narrow regions 9 is desirable and it has been proved that this can be fulfilled by local use of ultrasonics. In this respect, an ultrasonic probe has fitted thereto a suitably shaped tool which is conducted over the surface of the exposed semiconductor regions. The excavation is primarily effected by reason of the brittle properties of the amorphous silicon layer. By an appropriate choice of the bearing pressure of the tool on the silicon layer damage to the first electrode layer 2 lying thereunder as well as to the transparent substrate 1 can be avoided.The quality and reproducibiiity of this excavation process is determined by the bearing force, the shape of the hard-metal tip of the tool, the ultrasonic frequency, and the energy introduced by way of the ultrasonic probe, as well as the speed with which the tool is conducted over the layer. Ultrasonic frequency, bearing pressure and tool speed can lie in the following ranges: 10 up to 100 kHz, 100 to 500 p, 1 to 100 cm/s. Various alloyed ferrous metals are suitable materials for the hardmetal tip of the tool.

The individual solar cells 4, 8 etc., in accordance with Fig. 6, which are still electrically insulated from one another, now have to be connected together serially by appropriate contact elements. This is achieved, as shown schematically in Fig. 7, by introducing an electrically conductve paste, into the layer gaps afforded by the removed or excavated regions 7, 9, for example by screen printing, tampon printing, dosing systems or the like. The resulting contact elements 10 connect the respective second electrode layer 6 (metal) of each individual solar cell to the first electrode layer (TCO) 2 of the next adjacent solar cell.In the installation of the contact elements 10, it is necessary to take care that electrical contact is produced therethrough exclusively between the first electrode layer 2 of a respective solar cell and the second electrode layer 6 6 of its neighbouring solar cell, and that, in each case no short-circuit arises between the respective first electrode layers or the respective second electrode layers of neighbouring solar cells. In the case of the final embodiment in accordance with Fig. 7, the contact between the respective first electrode layers 2 (TOO) is already avoided by virtue of the semiconductor material remains in the regions 3 (in view of the appropriate arrangement of the regions 7 and 9). Futhermore, electrical contact between the respective second electrode layers (metal) 6 is avoided because the regions 7 are selected to be wider than the regions 9 and the electrically conductive paste forming the contact elements 10 in practice extends down into the region 9 and does not fill up the entire width of the region 7. In this respect, Silver conductive paste, which hardens after application, may suitably be chosen as the electrically conductive paste.

Claims (4)

1. A process for producing a solar cell arrangement in series connection and integrated thin layer technology, in which first of all a first electrode layer is applied over a large area of a substrate and then excavated in specific regions, then a semiconductor layer suitably structured for the conversion of incident electromagnetic radiation into electric energy is applied by vacuum deposition from the gas phase, over a similar large area, and in a further process cycle a second electrode layer is deposited over a similar large area and separate contact elements serving for series connection of the individual solar cells are applied, characterised in that the semiconductor layer and the second electrode layer are applied directly in succession by vacuum deposition, then the second electrode layer is removed in separate regions approximately following the pattern of the excavated regions of the first electrode layer, those regions of the semiconductor layer which are thus exposed are at least partially excavated, and finally the separate contact elements are applied in the layer gaps afforded by the removed and excavated regions of the second electrode layer and the semiconductor layer to provide electrical contact exclusively between the first and second electrode layers of respective neighbouring solar cells.

2. A process as claimed in claim 1, characterised in that the second electrode layer is a metal layer and is removed by etching in separate regions.

3. A process as claimed in claim 1 or 2, characterised in that the partial excavation of the semiconductor layer in the exposed regions is effected by local use of ultrasonics.

4. A process for producing a solar cell arrangement substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.