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Optimization of laser processing for PERC type c-Si solar cells

Genç, Ezgi
Passivated Emitter Rear Contact (PERC) type solar cells, which currently owns a similar market share as the standard type solar cells, is expected to be the dominant type of the photovoltaic (PV) market in near future (ITRPV, 2019) due to its high performance/cost ratio. Hence, it is critical to optimize PERC process steps to achieve higher efficiencies. In PERC concept, the stack of a passivation layer and SiNx capping layer is locally ablated to form low recombination and low resistive contacts. In this way, the total recombination at the rear side of the wafer is significantly reduced, leading to a higher open-circuit voltage and charge collection efficiencies in the base of the cell. In this thesis, the experiments which mainly focus on rear local contact formation were conducted with a picosecond laser of 532 nm wavelength to create local contact openings (LCOs). To determine the best laser performance in LCO process, the contact characteristics such as Al:BSF depth, contact width after firing, void fraction were correlated to laser fluence. To see the effects of these contact characteristics on solar cell performance and determine an optimized fluence range, efficiencies of the solar cells that were produced for each fluence were compared. For more detail investigation, corresponding efficiencies were calculated using Quokka simulation. Subsequently, the laser ablation process was optimized for the PERC production in Günam Photovoltaic Line (GPVL) and %19 efficiency has been achieved for the industrial-scale.