Silicon bulk issues during processing of homo-heterojunction solar cells
Résumé
In this work, an emerging cell concept based on silicon homo-heterojunction (HHJ) is investigated. Compared to the n-type silicon heterojunction cell (HET), the HHJ architecture contains an additional thin and highly doped (p +)c-Si layer at the front (i)a-Si:H/(n)c-Si interface. Using numerical simulations, advantages of the alternative architecture are first underlined. Especially, passivation improvements brought by the (p +)c-Si layer are evidenced through the study of the recombination rates in the whole cell. From the simulation results, the manufacturing issues of the HHJ cell are then addressed. Due to the need of a fully activated and shallow (p +)c-Si layer, ion implantation of boron is a promising candidate for making such cells. However, the efficient (i)a-Si:H passivation is very sensitive to substrate quality. Thus, the high temperature post-implantation annealing effect on the Cz substrates should to be assessed. An anneal at 1050°C, often required to fully activate Boron implanted emitters, strongly decreases the substrate lifetime and will impact drastically the HHJ cell performance. A 950°C annealing is found to limit considerably the substrate degradation. However, such rather low temperature will limit the maximum doping concentration of the implanted layer and thus the maximum achievable V OC in HHJ devices.
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