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.