The Effect of Surface Passivation at Low-Injection Level on Fill Factor of Silicon Heterojunction Solar Cells

32nd European Photovoltaic Solar Energy Conference and Exhibition; 831-834
In this paper, we present our study of fill factor (FF) loss mechanism for silicon heterojunction solar cells (SHJ) in relation to the quality of surface passivation. The effective minority carrier lifetime (eff) as a function of carrier injection density (n) has been modeled to identify the limiting factor of FF in our research. We have found that defects at a-Si:H/c-Si interface can cause low-quality surface passivation, which can be characterized by minority carrier lifetime at low-injection level, leading to reduction of fill factor. We propose a new mechanism that the presence of shallow defects with positive charges at the interface contributes to degradation of fill factor of SHJ cells. This hypothesis was verified using an AFORS-HET simulation tool in our study. Based on this study, we have developed an anti-contamination tray for wafer handling at the PECVD processing step. Our results show improvement of fill factor by an absolute value of 2%. SHJ solar cells with high efficiency of greater than 23% have been successfully fabricated using this technique.