Development and demonstration of a high-speed low-damage SiN laser ablation process
High throughput of >2000 wafers/h
Reduction of laser-induced damage to the emitter by use of ultra-short pulse lasers
Experimental studies for identification of laser-induced damage using various laser sources
Production and evaluation of laser-ablated cells with plated contacts
Main Project Achievements Laser ablation of Silicon Nitride was investigated in a study covering laser pulse durations from nanoseconds to femtoseconds. In the study, finished standard solar cells were used as a basis to evaluate laser-induced damage. By opening the SiN layer between the metal fingers and subsequent measurement of the electrical properties of the cells, the impact of laser-induced damage was determined for different laser sources. The laser delivered by Trumpf for the project proved to be highly suitable for the process.
The results were transferred to a small cell production for demonstration: in groups of 10 cells each, different laser parameters were applied, the samples were metallized using lithographic plating and then illuminated and dark I/V was measured. The results were unexpectedly bad, with large drops in Voc and efficiencies as low as 12%. Contact resistance measurements showed that the contact between laser ablated regions and plated metallization is low at the edges of the solar cells. The reason for this observation has to be identified by more in-depth analysis of the samples.
Independent of the laser source, the setup used for the process development allows processing times of the finger grid below one second, including busbars this increases to between 2 and 3 seconds. This highly depends on the required widths of fingers and busbars, which in turn depends on the method of subsequent metallization. For metallization techniques which do not require ablation of the busbars (e.g. plating of the fingers and subsequent printing of the busbars) a throughput of 3,600 wafers is thus possible.