Hydrogen Diffusion Mechanism In Polysilicon Solar Cells Deduced From Analysis Of Dopant Deactivation And Open-circuit Voltage Evolution

Résumé: The present work reveals a hydrogen diffusion mechanism in a polysilicon solar cell in order to achieve an effective passivation of defects and then high photovoltaic conversion efficiency. Plasma hydrogenation treatments were performed on polysilicon and monosilicon solar cells to witness, respectively, the evolution of the open-circuit voltage and the boron activation profile. The results obtained show clearly that the open-circuit voltage improves as the microwave plasma power increases. Nevertheless, the measured values are much higher for a less doped phosphorus emitter, which confirms that the hydrogen diffusion in the bulk of silicon is more prevented as well as the level of doping is high. However, the tendency of the open circuit-voltage values to saturation at high microwave plasma powers indicates that hydrogen can also produce new defects in polysilicon. This last observation has been well verified on monosilicon n+p solar cells. Also, hydrogen neutralizes boron and generates a concentration gradient between the boundary of the space charge zone and the depth of the p base region. As a result, we have admitted the existence of an electric field that encourages deep hydrogen diffusion atoms in the bulk of polysilicon. Moreover, the appropriate analysis of these results allowed us to propose a credible mechanism for hydrogen diffusion in polysilicon solar cells.

Publié dans la revue: Journal of New Technology and Materials