Laser processes are often used in the production of solar panels. Top hat beam shapers are used to enhance quality, throughput and efficiency of various laser ablation and scribing processes used in solar panel production.
The role of top hat laser beam shapers in the energy transition
In the past decade we all became more aware of the need for green sources of energy, such as solar and wind power, to replace polluting sources of energy such as fossil fuel and coal. One of the great hopes for this transition is the utilization of the sun’s radiation for production of electricity, aka. Solar power. The way to utilize solar power is through solar panels with photovoltaic cells. Top hat beam shapers have enabled a revolution in the way we produce solar panels and optimize the efficiency of the solar power collection process
What are Top-hat beam profiles?
A Top hat laser beam is a laser beam whose intensity profile is flat and uniform, with sharp edges where the energy drops rapidly to zero. The top hat beam shape can be a square, rectangle, line, circle or any other shape. The way we can transform a non-top-hat laser beam to a top hat beam profile is by using a top hat laser beam shaper which is a Diffractive Optical Element (DOE) designed to shape a gaussian, single mode laser beam into a top hat laser beam profile.
The use of top hat laser beam shaping in solar panels production
Top hat beam profiles are generally used for two main stages in the manufacturing of solar panels:
- Scribing of the top glass surface. The top layer of a solar panel in often some form of glass. These materials are often very reflective and prevent light from the sun to penetrate to the substrate of the photovoltaic cell and be converted into electricity. In order to avoid these reflections, a top-hat laser beam is used to scribe the top surface, making it diffusive and highly non-reflective, whilst retaining high transmissivity and non-absorption.
- Laser-forming of grooves to insert metal contacts into the photovoltaic substrate. Solar panels rely on the idea that electromagnetic radiation form the sun in the form of photons (the sun’s light) interacts with a semi-conductor substrate to release electrons via the photo-electric effect, and then transfer these electrons through a conductive material. Common buried electrode designs apply layers of these substances one on top of another, and scribe inlays to produce junctions between layers and transmission channels. These scribes, when done using a gaussian beam profile produce channel walls which are sloping, reducing profile width uniformity and wasting energy below the ablation threshold. Thanks to the sharp edges in the intensity profile of top-hat laser beam profiles, these channels can now be scribed with very smooth and uniform walls , ensuring consistent electrode width and utilizing the laser energy efficiently, thus increasing throughput.
- Reducing Heat Affected Zones (HAZ). When trying to perform any laser process in a material (e.g. laser scribing in solar panels), there is a threshold energy at which this process can occur, and any energy lower than it, while insufficient for the process, can induce unwanted processes in the substrate near the processed area, such as burning, scorching, discoloration, expansion and others. The areas affected by these side processes are called Heat Affected Zones. These HAZs reduce both the process speed and the efficiency of the solar panel due to damaged regions which are unable to convert light into power and are thus unwanted. When using a gaussian beam or any other non-top-hat laser beam distribution, some areas of the laser beam provide the material with energy below the threshold level and create HAZs. Since top-hat laser beam profiles provide a uniform intensity distribution, HAZs are reduced to a minimum and efficiencies improve significantly.
TL; DR – Q&A SUMMARY
What is a top hat laser beam?
A top hat laser beam is a laser beam whose intensity is shaped to be flat and uniform, with sharp edges that decrease rapidly to zero intensity.
Why are top-hat laser beam profiles better than gaussian profiles for solar panel planning and manufacturing?
Due do their flat top intensity and well-defined boundaries, top-hat laser beam profiles enable highly delicate manufacturing to be done with excellent precision. This enables us to design better and more efficient designs for modern solar panels, as well as reduced HAZs.
Why do glass top-surfaces for solar panels need top hat laser beam profiles?
Glass top-surfaces for solar panels are often highly reflective and do not allow most of the suns light to be absorbed by the photovoltaic cell in order to produce electricity. Top hat laser beams enable one to produce laser-structuring on top of the glass surface in order to make it diffusive and non-reflective.
How do top hat laser beam shapers improve buried contact solar cells production?
By allowing better, sharper edged ablation of the trenches used for the buried contacts, more surface junction area between the photovoltaic substrate and the conductor is achieved with less loss of active photovoltaic bulk.