Atomic hydrogen passivation for photoresponsivity enhancement of boron-doped p-BaSi₂ films and performance improvement of boron-doped p-BaSi₂/n-Si heterojunction solar cells

Semiconducting barium disilicide (BaSi₂) is an emerging material for solar cell applications, and therefore, defect passivation is critical for improving its solar cell performance. Herein, the effect of atomic hydrogen (H) on the photoresponsivity of 500 nm-thick boron (B)-doped p-BaSi₂ films was examined. The photoresponsivity reached ∼4 A/W (about twice the highest reported value for H-passivated undoped BaSi₂ films) in B-doped p-BaSi₂ films exposed to an atomic H supply for 5 − 10 min because of an increased minority-carrier lifetime, as measured by the microwave-detected photoconductivity decay. Furthermore, a ≥15 min atomic H supply was found to degrade photoresponsivity. Ab initio studies were used to interpret and understand experimental observations by analyzing states in the gap region, which can act as traps, in B-doped p-BaSi₂ with H incorporation. The effect that atomic H had on the performance of B-doped p-BaSi₂/n-Si heterojunction solar cells was also studied. The saturation current density was found to decrease by three orders of magnitude with the atomic H supply, and the conversion efficiency was increased up to 6.2%. Deep-level transient spectroscopy revealed a reduction of defect densities induced by the atomic H supply. Both experimental and theoretical viewpoints show that an atomic H supply is beneficial for BaSi₂ solar cells.