ROFIN Reveals Dual Line c-Si Laser System
ROFIN-BAASEL Lasertech is launching a new, upgraded version of its production proven Dual Line c-Si laser processing system that the company says provides improved productivity and lowers processing costs in volume production of next-generation PERC (Passivated Emitter and Rear Cells) solar cell design.
The latest Dual Line c-Si modular platform will be unveiled at the SNEC 2014, being held in Shanghai, China at the Shanghai New International Expo Centre.
Initially launched over 3 years ago, the Dual Line c-Si laser processing system has already been installed at multiple leading PV manufacturer's facilities worldwide that are focused on PERC and selective emitter processes for improvements of up to a 1% absolute efficiency gain and higher productivity that lowers production costs.
Fig. 1: PERC "“ drilling of round dots
"˜Future Fab' Project researching solutions for sub-surface damages
Key technical developments for PERC cells undertaken within the Photovoltaics Innovation Alliance "˜FutureFab' project, funded by the German Federal Ministry of Education and Research (BMBF), included in-depth analysis of short wavelength and short pulse laser tool requirements to minimize sub-surface damage during rear-side contact hole formation and optimize rear side passivation.
"The study revealed that complex ultra short femto and picosecond lasers create completely different surface structures after laser ablation of dielectric layers compared to nanosecond laser pulses", said Jens Theobald R&D Engineer at International Solar Energy Research Center Konstanz. "However, after the BSF [Back Surface Field] formation, studies showed that rear side passivation opening using green nanosecond laser pulses lead to the same level of high efficiency solar cells as it does with ultra violet picosecond pulses."
Important to the optimization of the process was the ability to use industrial lasers offering up to 5 times higher power compared to the previously used nanosecond laser source, reducing laser process cycle times per wafer significantly and improving overall wafer throughput, critical to volume production applications.
The Dual Line c-Si can now be equipped with a high power ns-SHG-laser with adapted beam profile specifically developed for the creation of larger dot diameters without increasing the laser induced damage. This patent pending process for a dot style opening of the passivation layers leads to scan-speeds exceeding 20 m/s. This is a significant breakthrough for PERC cells employing dot pattern designs, as laser ablation cycle times are reduced significantly and thus enabling lower production costs.
"˜On the fly' processing for elimination of handling and transfer times
The Dual Line c-Si™ system also features the inclusion of "˜on the fly' processing, a new system that virtually eliminates wafer handling and transfer times between laser processing cycles, improving productivity by providing processing speeds of up to 3,600WPH (Wafers-Per-Hour)
ROFIN has recently received tool orders PERC cell processes for use in R&D development work as well as high-volume production line applications. The Dual Line c-Si has demonstrated > 20% for monocrystalline (mono-c-Si) and > 18% for multicrystalline (multi-c-Si) p-type cells could be achieved with the equipment, providing up to a 1% absolute efficiency gain.
Further developments are underway that are expected to lead to "˜on the fly processing throughputs even beyond 4000 WPH.
Fig. 2: For higher PERC solar cell productivity; ROFIN's Dual Line c-Si
The Dual Line c-Si is a modular machine platform designed for high throughput solar cell manufacturing with multiple installations at leading PV manufactures worldwide. The core of the machine is a high precision granite base to support laser optics and rapid wafer handling units. It is equipped with two independently operating lines for cell transport and one laser process chamber each. In general the machine can be placed in-line with other processing machines or configured with stack and/or cassette handling systems for batch type operation.
