Oxygen‐alloyed poly‐Si passivating contacts for high‐thermal budget c‐Si heterojunction solar cells
Guangtao Yang, Can Han, Paul Prócel, Yifeng Zhao, Manvika Singh, Luana Mazzarella, Miro Zeman, Olindo Isabella
Abstract
Abstract 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‐SiO x ) as suitable material for passivating contacts. From passivation point of view, poly‐SiO x layers show excellent passivation quality and carrier selectivity for both n ‐type (i V OC,flat = 740 mV, contact resistance ρ c = 0.7 mΩ/cm 2 , i V OC,textured = 723 mV) and p ‐type (i V OC,flat = 709 mV, ρ c = 0.5 mΩ/cm 2 ). Optically, due to the incorporation of oxygen, the absorption coefficient of poly‐SiO x becomes much lower than that of doped poly‐Si at long wavelength. Both n ‐type and p ‐type poly‐SiO x 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‐SiO x FBC cell, with the potential of further improvement in both V OC and FF . The optical advantage of poly‐SiO x over poly‐Si as passivating contact is also observed with a 19.7% interdigitated back‐contacted (IBC) solar cell endowed with poly‐SiO x emitter and back surface field. Compared to the reference 23.0% IBC solar cell with poly‐Si passivating contacts, the one based on poly‐SiO x passivating contacts shows higher IQE at wavelengths above 1100 nm. This indicates that for both FBC and IBC cells, poly‐SiO x passivating contacts hold potential in enhancing the cell J SC by maximizing the cell spectral response.