Effect of the band gap of the window layer on the properties of silicon heterojunction solar cells

The effect of the band gap of the window layer on the properties of silicon heterojunction solar cells was performed by a set of AMPS simulations. The results show that the short-circuit current increases slightly with the band gap of the window layer, E
_g2
, increasing. At the ideal defect-free interface case or negligible interface states, E
_g2
almost has no effect on the open-circuit voltage V
_OC
and the fill factor FF at E
_g2
<; 1.9 eV. At non-negligible interface states, since the valence band offset can saturate part of interface states, V
_OC
increases with E
_g2
increasing; at E
_g2
<; 1.9 eV, FF increases slightly with E
_g2
increasing. However, at E
_g2
≥ 1.9 eV, S-shaped J-V characteristic occurs. It results in the decrease of FF and then the conversion efficiency. The optimum efficiency was obtained for silicon heterojunction solar cells at E
_g2
= 1.7 - 1.8 eV. The optimum window layer material corresponds to a-Si:H.