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

Crystalline 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 (iV(OC,flat) = 740 mV, contact resistance rho(c) = 0.7 m omega/cm(2), iV(OC,textured) = 723 mV) and p-type (iV(OC,flat) = 709 mV, rho(c) = 0.5 m omega/cm(2)). 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 J(SC,EQE) = 39.7 mA/cm(2) is obtained in front-side textured poly-SiOx FBC cell, with the potential of further improvement in both V-OC 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 J(SC) by maximizing the cell spectral response.

Automated summary

The use of oxygen-alloyed poly-Si (poly-SiOx) as passivating material in crystalline silicon solar cells shows excellent passivation quality, carrier selectivity, and reduced optical losses, leading to improved cell efficiencies and potential for further enhancements in both V-OC and FF.