Superior laser processing with flat top profiles in solar cell technology

Direct laser patterning of various materials has found its way into several micro-system production lines like inkjet printing, solar cell technology, flat-panel display production, semiconductors and medical treatment. Typically, TEM00 single-mode solid state lasers and their higher harmonics are used, especially for machining of holes and trenches. The most prominent lasers are short pulse solid-state lasers based on Nd-doped gain materials and their harmonics @ 266, 355 and 532 nm. Traditionally, the original Gaussian beam profile is used. With optimised top hat optics the quality of the generated micro-structures - especially straightness and steepness of the edges - can be improved. Additionally, the process time can be reduced since for a top hat profile less energy is lost in the shoulders of the profile compared to a Gaussian one. Based on LIMO’s unique production technology free-form refractive optics were developed which exhibit high efficiencies (> 98%) and inhomogeneities below 10 %. With optimized depths of field above +/-300 µm and integration into industrial scanning systems these optics can boost the performance and throughput in laser-based solar cell manufacturing lines. Processing results are demonstrated for various laser-based processes in thin film (e.g. P1, P2 and P3) as well as crystalline Silicon solar cell production