Influence of SiOx film thickness on electrical performance and efficiency of TOPCon solar cells

Abstract

The tunnel oxide passivated contact solar cells (TOPCon) on n-type Cz Si wafers instead of passivated emitter and rear solar cells are currently migrated to mainstream production, with ongoing improvements in recent years. In this study, we investigated and characterized one recent batch of TOPCon cells fabricated on 156.75 × 156.75 × 0.18mm3 wafers with fully screen-printed technology by an industrial-type process. TOPCon cells with an efficiency as high as 22.43%, a Voc value as high as 689.4 mV, and a fill factor as high as 81.35% were obtained. The P dopant diffusion in the poly Si layer as well as the thickness of the SiOx layer were optimized in order to obtain good electrical contact between screen-printed Ag and Si. The thickness of the SiOx layer should be over 1.5 nm, which is beneficial for obtaining a good passivation for the cells. The surface P dopant concentration in the polycrystalline Si was higher than 1 × 1020 atom/cm3, resulted in a low series resistance and a high fill factor. The characterization and simulation results show that both metal shading loss and rear surface recombination were dominant among all of the losses. Application to solar cells with a Voc of 697 mV and a fill factor of 82.45% could lead to an independently confirmed cell efficiency of over 23% for n-type cells with poly Si the herein developed passivated rear contacts, and the front metal contacts by addressing the issue of reducing metal recombination and implementing a selective emitter.