Improvement of Ag(In,Ga)Se2/Mo Interface and Solar Cell Performance by Preselenization of the Mo Back Contact

In Ag(In,Ga)Se
₂
(AIGS) solar cells, a MoSe
₂
thin layer may provide a critical contact between the AIGS layer and the Mo layer. To test this, AIGS films were deposited on Mo-coated substrates without and with preselenization. With preselenization, the MoSe
₂
thickness in the AIGS samples ranged between 30 nm and 60 nm, while no MoSe
₂
layer was observed for the AIGS samples without preselenization. The c-axis of the MoSe
₂
layer was parallel to that of the Mo layer, with c = 12.5 Å. The presence of MoSe
₂
in the AIGS films was confirmed by secondary ion mass spectrometry and preselenization exhibited no effect on the promotion of sodium diffusion in the AIGS films. Without preselenization, the AIGS and Mo had a Schottky contact with a calculated barrier height between 0.66 and 0.74 eV, based on the AIGS/Mo current-voltage curves. In contrast, the MoSe
₂
layer converted the AIGS and Mo contact to an ohmic type. Preselenization increased the solar cell conversion efficiency of AIGS to 9.3% (open-circuit voltage: 957.9 mV, short-circuit current: 18.4 mA/cm
²
, and fill factor: 52.9%). Additionally, the quantum efficiency was improved. In the absence of preselenization, the conversion efficiency was 5.2% (open-circuit voltage: 850.6 mV, short-circuit current: 13.1 mA/cm
²
, and fill factor: 46.7%).