Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With housing or contact structure
Reexamination Certificate
2001-05-24
2003-05-06
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With housing or contact structure
C136S255000, C136S256000
Reexamination Certificate
active
06559479
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin-film solar cell array system and a method for producing the same.
2. Description of the Prior Art
Solar cells are components which convert light into electric energy. Usually they comprise a semiconductor material containing n-type and p-type zones, i.e. zones in which current is transported by means of respectively negative and positive charge carriers. These zones are referred to respectively as the emitter and the base. The positive and negative charge carriers generated by incident light are separated and can be conveyed by means of metallic contacts on the respective zones. Only those charge carriers contribute to useable electric power that reach the contacts and do not recombine with a charge carrier of reverse polarity. A further loss mechanism is the reflection of light at the metal contacts, referred to as contact shading the solar cell. The smaller the shading, i.e. the more light which is able to reach the solar cell, the greater the current exploitation by the cell per area and therefore the greater the efficiency. The contacts on the light-facing side, usually the front surface of the cells, are usually designed as comb-shaped structures, so-called grids. However, in order to ensure current conveyance with little resistance, the spacing of the grid fingers must not be selected too large and the number and cross section must not be selected to be too small. A certain amount of shading must be taken into account in conventional solar cells.
With the development of cheaper starting materials, the concept of thin-film solar cells on cost-favorable substrates is gaining more significance. One such known solar cell (see
FIG. 1
a
) comprises only one active solar cell layer
1
comprising a p-type doped base zone
1
b
and, in the depicted instance of
FIG. 1
a
, n-typed doped selective emitter zones
1
a
. The active solar cell layer
1
applied to a carrier substrate
2
usually possesses a thickness of approximately 3-50 mm. However, many such substrates
2
are not conductive. Therefore, the electrical contact to base
1
b
cannot occur from the back surface via the carrier substrate
2
. Instead a so-called single-side grid comprising two intermeshing grids, an emitter grid
3
a
and a base grid
3
b
, for contacting the emitter
1
a
and the base
1
b
respectively must be employed.
Such a solar cell array system can be simultaneously used for connecting multiple solar cells on a carrier substrate as described in DE 197 15 138.
U.S. Pat. No. 4,490,573 describes a solar cell. See in particular the embodiment of
FIG. 8
, which is provided with a contact layer
51
applied onto a glass substrate
52
and is electrically connected via contacting zones with, for example the n-type doped zone of a solar cell layer
54
. Solar-cell layer
54
is produced by means of gradual doping using the doping atoms arsenic and bromide. This is essentially illustrated in FIG.
9
and the respective description. Contact electrodes
16
are placed directly on the p-typed doped layer of the solar cell layer. Therefore, the electrode structures are provided on both sides of the solar cell layer and shade the solar cell layer at least partially from unimpeded irradiation.
The solar cell described in WO89/04062, providing a multilayered solar cell array system, has the same drawback. See in particular the embodiments of
FIGS. 1
a
and
b
.
FIG. 1
b
essentially shows a first electrode
14
placed directly on a glass substrate on which the silicon-based solar cell layer is applied. A second electrode layer, which is interrupted by dielectric zones
20
, is in direct contact with solar cell layer
16
. A gridlike electrode structure
32
, which is connected to the solar cell layer
16
and to the first electrode layer
14
via the electrically conducting connecting channels
22
, is placed on the dielectric layer
20
.
FIG. 1
b
shows a similar known arrangement for a back-contact cell, a concept for highly efficient solar cells. In this case, both contacts
3
a
and
3
b
are placed on the back surface of the solar cells to completely eliminate shading on the front surface. If the contacts are realized as narrow grids, light that reaches from the back surface through to the front surface can also contribute to generating electricity (so-called bifacial cell).
Hitherto realization of this single-side grid has only been possible by means of very complicated processes. The selective emitter is created by multiple masking steps: the emitter does not comprise a homogeneous lateral layer but rather comprises a subzone corresponding to the shape of the emitter grid. In this manner, base zones are retained on the surface and can be directly contacted. Placing the respective metal contacts precisely on the corresponding zones poses a critical alignment problem and also requires masks, which must be accurately aligned.
Such a type back-contact cell is described in JP 2-51282 and is known as emitter wrap through (EWT). However, an EWT cell is limited to solar cells made of silicon disks respectively wafers. But the essential cost-saving potential in photo-voltaic cells lies in reducing the use of the expensive silicon to only a few- micrometer-thick layer, so-called thin-layer solar cells. As a carrier substrate is a prerequisite for these thin-layer solar cells, their back surface is not accessible and the known EWT process cannot be applied. At the same time, due to this minimal thickness, thin-layer cells permit using silicon of poorer quality than for conventional or EWT solar cells.
SUMMARY OF THE INVENTION
The present invention provides a thin-layer solar cell array system having, placed over a carrier substrate of plane design, a solar cell layer having at least one n-type conducting semiconductor layer zone (emitter) and at least one p-type conducting (base) semiconductor layer zone as well as a first and a second contact electrodes each of different electrical polarity, which are each electrically connected respectively to the emitter and the base in such a way that a solar cell can be produced in a simpler and less expensive manner without impairing the efficiency of the solar cell. Contrary to the state of the art, the electrical contact of the individual semiconductor zones occurs without using masks which require highly accurate alignment and is realizable using simpler methods. Furthermore, the thin-layer solar cell array of the invention permits simple interconnection of multiple solar structures on a carrier substrate as well as allowing provision of a protective diode. In particular, the thin-layer solar cell array system provides the connecting electrodes only on one side of the solar cell layer to, in this manner, have as few as possible shading losses due to the electrode structures. Finally, the invention is a method for producing the novel thin-layer solar cell array system.
The thin-layer solar cell array system of the invention places over a carrier substrate of plane design, a solar cell layer with at least one n-type conducting semiconductor zone, the emitter zone, and at least one p-type conducting semiconductor zone, the base zone, as well as a first and a second contact electrode each of different electrical polarity, which are each respectively electrically connected to the emitter and to the base. The thin layer solar cell is designed in such a manner that the first and the second contact electrodes are applied directly or separated by an electrically insulating layer on the carrier substrate over which an electrically insulating layer is provided with the solar cell layer placed over this insulating layer. The contact electrodes are preferably designed as grid-shaped strip conductors and are made of metal or other highly conductive materials. The two contact electrodes, which are electrically connectable to different polarities, are placed spaced apart on the carrier substrate.
For electrical contacting of the respective semiconductor layer zones (emitter zone, base zone)
Antoneli, Terry, Stout & Kraus, LLP
Berry Renee R.
Fraunhofer-Gesellscahft zur Forderung der angewandten Forschung
Nelms David
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