Laser Structuring

Laser technology is outstandingly suited for microstructuring crystalline solar cells. It enables a high throughput and can be reliably integrated into production lines. It is economical and high-throughput relative to other methods such as masking or electron beam processes. Additional advantages are non-contact energy coupling, flexible beam guidance, high accuracy, and rapid positioning as well as the exact control of energy infeed. Material damage is avoided.

Different laser sources ranging from nanosecond lasers to ultra-short pulse lasers in combination with scanner systems are possible to use depending on customer requirements concerning quality, throughput, and investment costs.

Nanosecond lasers score points mainly in terms of throughput and cost efficiency. However, due to pulse duration, relatively more heat is conveyed into the material than with ultra-short pulse lasers.

Laser ablation with ultra-short laser pulses having pulse durations in the pico and femtosecond range (10-13 s to 10-15 s) is often described as “cold ablation”. However, this only applies to pulse durations less than ten femtoseconds. If the pulse duration lies above this time interval, an electron-photon interaction and the associated temperature conduction occur in the substrate. Ideally this restricts itself to less than 100 nm of material width at pulse durations into the picosecond range. The ultra-short pulse laser’s advantage lies in its feature of imparting all of the laser energy to the material within a very short time interval. Extremely high power densities up to a few gigawatts per cm² are thereby achieved. This leads to very good absorption of the laser radiation and the associated possibility of processing quasi “athermal” and extremely precisely. The result is qualitatively high-value structures with practically no heat influence or material contamination on the surrounding material.

Ultra-short pulse lasers can be integrated as reliably into fabrication processes as nanosecond lasers; however, in comparison with the latter the former are clearly more cost intensive both to acquire and to maintain.

Laser Systems for Structuring