Metallization‒induced recombination losses of bifacial silicon solar cells

In this study, we investigate the metallization‒induced recombination losses of high efficiency bifacial n‒type and p‒type crystalline Si solar cells. From the experimental data, we found that the most efficiency limiting parameter by the screen‒printed metallization is the open‒circuit voltage (VOC) of the cells. We investigated the mechanism responsible for this loss by varying the metallization fraction on either side of the cell and determined the local enhancement in the dark saturation current density beneath the metal contacts (J0(met)). Under optimum fabrication conditions, the J0(met) at metal‒p+ (boron) emitter interfaces was found to be significantly higher compared with the values obtained for metal‒n+ emitters. A two‒dimensional simulation model was used to get further insight into the recombination mechanism leading to these VOC losses. The model assumes that metal contacts penetrate (or etch) into the diffused region following the firing process and depassivate the interface. Applying this model to our n‒type solar cells with a boron p+ emitter, we demonstrated that the simple loss of passivated area beneath the metal contact cannot explain the degradation observed in the VOC of the cell without considering a significant etching or metal penetration into the emitter region. Copyright © 2014 John Wiley & Sons, Ltd.