Oxygen‐alloyed poly‐Si passivating contacts for high‐thermal budget c‐Si heterojunction solar cells

Abstract

AbstractCrystalline silicon solar cells with passivating contacts based on doped poly‐Si exhibit high optical parasitic losses. Aiming at minimizing these losses, we developed the oxygen‐alloyed poly‐Si (poly‐SiOx) as suitable material for passivating contacts. From passivation point of view, poly‐SiOx layers show excellent passivation quality and carrier selectivity for both n‐type (iVOC,flat = 740 mV, contact resistance ρc = 0.7 mΩ/cm2, iVOC,textured = 723 mV) and p‐type (iVOC,flat = 709 mV, ρc = 0.5 mΩ/cm2). Optically, due to the incorporation of oxygen, the absorption coefficient of poly‐SiOx becomes much lower than that of doped poly‐Si at long wavelength. Both n‐type and p‐type poly‐SiOx layers are concurrently deployed in front/back‐contacted (FBC) solar cells with a front indium tin oxide (ITO) layer to facilitate the lateral transport of carriers and minimize cell's reflection. A high cell FF of 83.5% obtained in double‐side flat FBC solar cell indicates an efficient carrier collection by these passivating contacts. An active‐area cell efficiency of 21.0% featuring JSC,EQE = 39.7 mA/cm2 is obtained in front‐side textured poly‐SiOx FBC cell, with the potential of further improvement in both VOC and FF. The optical advantage of poly‐SiOx over poly‐Si as passivating contact is also observed with a 19.7% interdigitated back‐contacted (IBC) solar cell endowed with poly‐SiOx emitter and back surface field. Compared to the reference 23.0% IBC solar cell with poly‐Si passivating contacts, the one based on poly‐SiOx passivating contacts shows higher IQE at wavelengths above 1100 nm. This indicates that for both FBC and IBC cells, poly‐SiOx passivating contacts hold potential in enhancing the cell JSC by maximizing the cell spectral response.