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Ion implantation for all-alumina IBC solar cells with floating emitter
Interdigitated back contact (IBC) solar cells have a high efficiency potential. However, the fabrication of this cell structure is quite complex. Ion implantation for structured doping together with batch reactors for front and rear side passivation with Al2O3 could help to reduce the fabrication effort. Since Al2O3 gives a very good passivation on p-doped surfaces, we investigate n-type IBC solar cells with a low-dose ion-implanted front floating emitter (FFE) which we compare to a low-dose ion implanted front surface field (FSF) passivated by SiO2. We measured saturation current densities (J0) between 10 and 15 fA/cm2 for the SiO2 passivated FSF and down to 5 fA/cm2 for the Al2O3 passivated FFE on textured samples. The FFE has been successfully applied to fully implanted IBC cells (η = 21.8 %). Cells with FSF degraded strongly under UV-illumination due to the instable SiO2 passivation on the front side while the FFE cells with Al2O3 passivation were much less affected. IV measurements under low level illumination revealed a linear performance down to 0.01 suns for both, FSF and FFE.