Modular Beam Splitting System MBSS for efficient solar cell production

Photovoltaic manufacturers must produce more cost-effectively and efficiently in order to ensure that solar cells, such as perovskite solar cells (PSC), can continue to be used as sustainable renewable energy on a large scale.  The requirements for a laser system in the context of their production are very demanding: high accuracy, fast process times and high throughput rates. Jenoptik's modular beam splitting system is designed for precisely these requirements. It is used in all three process steps P1, P2 and P3 of laser structuring and can achieve extremely precise and reliable results in a significantly shorter time thanks to its parallel laser scribing. In addition, the MBSS enables very narrow and sharp P1-P2 and P3 lines. This allows a much larger “active area” and reduces the so-called “dead zone”. 

The three downstream process steps of laser structuring are crucial for a consistent cell connection in the module:

• P1: Separating adjacent cells by removing the bottom electrode
• P2: Exposing the lower electrode to connect the upper and lower electrodes when the material for the upper electrode is applied
• P3: Separating neighboring cells by removing the upper electrode

The quality of the laser structuring process therefore has a direct impact on the so-called “cell-to-module losses” and thus also on the efficiency of the photovoltaic system. All the more reason to use high-performance optical solutions such as the Modular Beam Splitting System to keep manufacturing processes stable, costs low and product quality high. 

Jenoptik´s MBSS module has more stable beam splitter performance regarding to the variation of laser beam point direction. The MBSS output beams will tilt as a group if the point direction of input laser beam vary slightly. There is no impact to intensity uniformity or pitch uniformity for laser scribing.
For the approach with a classical beam splitter, Input laser beam tilt may cause the shift of beam incident location on each mirror, which result in variation of the pitch uniformity for output beams. See image below.

Depending on the requirements, the number and spacing of the laser beam spots can be specified in addition to the wavelength when configuring the MBSS. The Modular Beam Splitting System is then designed and supplied accordingly. Once integrated into the overall system, the optical system also offers the option of easily and effortlessly readjusting or fine-tuning the beam spot spacing (pitch) using a simple rotating mechanism. This saves costs and time - not only when setting up the system for the first time, but also when making changes, e.g. when replacing a laser. To adjust the spot size, it is of course also possible to add a beam expander and combine it with the MBSS.

For perovskite solar cell P3 laser scribing process, it is necessary to add beam shaping component to generate top-hat array. 
A top hat beam shaper, for example, can be used to  create certain shapes, like circles, squares, rectangles, lines, or others. As a diffractive optical element (DOE) the Beam shaper convert a near-Gaussian laser beam into a uniform-intensity spot with sharp edges. The result is a beam with a consistent intensity distribution across its entire surface, which is perfect for applications that require precise control over the beam's shape and intensity.

MBSS approach generates top-hat array by integrating single DOE beam shaper element. The beam shaper alignment takes only one time so much less efforts than traditional beam splitter system. In addition, MBSS multiple beams are emitted through a single optical system, therefore optimized top-hat array locate at the same focal plane, have equal top hat size with the same intensity distribution With MBSS, multiple beams are emitted through a single optical system. This makes it possible to utilize the entire depth of focus range of the lens.

Disadvantages of a classical beam shaping array with mirrors and DOEs: 

• Individual DOE beam shaper for each channel need a lots of efforts for top-hat calibration.
• Objectives focal length variation results in the deviation of top hat size, top hat intensity, and the intensity distribution in top hat.
• The deviation of individual focal length may cause unequal top-hat size. Individual beamlet de-focus status result in uneven ablation effect on workpieces.

 

Imagine it like this: When you take a picture, the lens projects an image onto the camera sensor. The depth of focus (DOF) is the range in which the sensor can be moved without affecting the quality of the image. For perovskite solar cell (PSC) laser scribing, depth of focus (DOF) means the axical range where the focusing spot keeps the same size, therefore laser scribing line width has no change. In the other words, DOF indicated the acceptable flatness error of rigid PSC or the acceptable defocusing amount of flexible PSC. Here we are talking about the application DOF of the laser scribing system. 

With Jenoptik's Modular Beam Splitting System, multiple beams are emitted through a single optical system. This makes it possible to utilise the entire DOF range of the lens. 

The MBSS solution provides a value of DOF >+/-1.0mm. This means that there is no need to integrate a focus tracking system into the laser system. In addition, the larger depth of focus (compared to existing optical setups) allows Jenoptik's MBSS to be used for both rigid and flexible perovskite solar cell laser scribing processes.

MBSS is compact and light weight optical module, < 10kg only! It can be installed in laser scribing system conveniently. The light weight enables driving MBSS module and flying the laser beams to realize laser scribing process. Flying laser beam is proved an effective solution for high speed, precise and realiable laser scribing in film solar laser scribing production. 

Due to the light weight, MBSS can be installed flexibly in the way of laser scribing from bottom to up for inputing via glass side, or laser scribing from up to down for inputing via the film side.