20.8% industrial PERC solar cell: ALD Al2O3 rear surface passivation, efficiency loss mechanisms analysis and roadmap to 24%

PERC cell is currently entering the industrial crystalline silicon solar cell production lines. While there has been many reports focusing on research PERCs, this paper aims to present a cost-efficient PERC roadmap at fully industrial level, i.e. beyond the research and pilot lines. We present a systematic experimental study on the most important material and cell parameters for PERC, for instance, the key processes of ozone based ALD Al2O3 rear surface passivation and screen printed aluminum local back surface field are discussed in detail, especially highlighting the importance of the process integration. Industrial PERC cells using this roadmap have demonstrated average efficiency of 20.5% and champion efficiency of 20.8% with open circuit voltage of 660-666 mV. Light-induced degradation analysis shows that the PERC cells are subject to bulk degradation and not to surface degradation. An anti-LID treatment processed by simultaneous applying forward voltages and anneal can drastically decrease LID. The cell efficiency loss mechanisms are analyzed based on the quantum efficiency measurement, suns-V-oc tests and series resistance loss calculations. These are combined with PC1D and PC2D simulations to analyze recombination loss mechanisms present in the cells in order to promote viable solutions to extend the current industrial PERC cell efficiency to 24%.