magnitudes less conductive than the transparent front contact. Similarly, the P3 scribes
forms an insulating gap in the metallic back contact. However, the P2 scribe that is also
filled with metal forms a highly conducting connection between the front and back
contacts – this is where the actual series connection is performed.
For example, for making CIGS-based PV modules, first the molybdenum back
contact is deposited on top of the glass substrate and the cell areas are defined by P1 laser
scribes. Then the CIGS p layer and the CdS n layer are deposited including a P2 laser
scribe step. Finally the intrinsic and n-doped zinc oxide is deposited, followed by a final
P3 laser scribe step. Now the front TCO electrode is connected with the molybdenum back
contact of the next solar cell.
The performance of such an interconnect established via laser scribes and hence the
total module performance is determined by several things. First, the P2 scribe has to be
highly conductive. This means that it has to be wide enough and that there must be no
barrier at the interface between the front contact and the metal of the P2 scribe. Further,
the P1 and P3 scribes must form good barriers to separate the cells from each other
effectively. Thirdly, the region between the P1 and P3 scribes does not contribute to the
current generated by the module. Therefore, the ratio between this width and the total cell
width (including the scribes) has to be as small as possible in order to keep the active area
of the module as large as possible. Another issue is the fact that the three laser scribes are
performed in different steps of production and thus often with different machines. Further,
the distance between the scribes might be different at the different processes when they are
performed at different temperatures. Thus, aligning the glass plates in all the production
steps is extremely important for manufacturing high quality thin-film modules.
The production steps and also the exact processing of the laser scribes is of course
dependent on which thin-film technology is used and even on the manufacturer itself.
However, the basic principles and the action behind these processes is valid in general.
One advantage of thin-film PV technology is that flexible modules can be made. For
example, at the Dutch company HyET Solar, thin-film silicon layers are deposited onto a
temporary aluminium substrate [114] that is etched away during the production process.
This results in a low weight flexible substrate, which can be integrated for example into
curved rooftop elements. A big advantage is that such very light modules can be installed
on weak roofs that would be unable to support heavy PV panels. Further, if such flexible
modules are directly integrated into roofing elements, installation costs could be reduced
significantly. Often, installation costs are the largest contributor to the non-modular costs
of a PV system. Currently, only thin-film silicon technologies have demonstrated flexible
modules with reasonable efficiencies.
forms an insulating gap in the metallic back contact. However, the P2 scribe that is also
filled with metal forms a highly conducting connection between the front and back
contacts – this is where the actual series connection is performed.
For example, for making CIGS-based PV modules, first the molybdenum back
contact is deposited on top of the glass substrate and the cell areas are defined by P1 laser
scribes. Then the CIGS p layer and the CdS n layer are deposited including a P2 laser
scribe step. Finally the intrinsic and n-doped zinc oxide is deposited, followed by a final
P3 laser scribe step. Now the front TCO electrode is connected with the molybdenum back
contact of the next solar cell.
The performance of such an interconnect established via laser scribes and hence the
total module performance is determined by several things. First, the P2 scribe has to be
highly conductive. This means that it has to be wide enough and that there must be no
barrier at the interface between the front contact and the metal of the P2 scribe. Further,
the P1 and P3 scribes must form good barriers to separate the cells from each other
effectively. Thirdly, the region between the P1 and P3 scribes does not contribute to the
current generated by the module. Therefore, the ratio between this width and the total cell
width (including the scribes) has to be as small as possible in order to keep the active area
of the module as large as possible. Another issue is the fact that the three laser scribes are
performed in different steps of production and thus often with different machines. Further,
the distance between the scribes might be different at the different processes when they are
performed at different temperatures. Thus, aligning the glass plates in all the production
steps is extremely important for manufacturing high quality thin-film modules.
The production steps and also the exact processing of the laser scribes is of course
dependent on which thin-film technology is used and even on the manufacturer itself.
However, the basic principles and the action behind these processes is valid in general.
One advantage of thin-film PV technology is that flexible modules can be made. For
example, at the Dutch company HyET Solar, thin-film silicon layers are deposited onto a
temporary aluminium substrate [114] that is etched away during the production process.
This results in a low weight flexible substrate, which can be integrated for example into
curved rooftop elements. A big advantage is that such very light modules can be installed
on weak roofs that would be unable to support heavy PV panels. Further, if such flexible
modules are directly integrated into roofing elements, installation costs could be reduced
significantly. Often, installation costs are the largest contributor to the non-modular costs
of a PV system. Currently, only thin-film silicon technologies have demonstrated flexible
modules with reasonable efficiencies.