Fabrication of a GaAs/GaNAsBi solar cell and its performance improvement by thermal annealing

To evaluate the performance of GaNAsBi alloys as solar cell materials, a GaNAsBi double-heterostructure pin solar cell was fabricated using plasma-assisted solid source molecular beam epitaxy. The addition of even a small amount of N (less than 1%) to the GaAsBi alloy significantly reduces the short-circuit current density (Jsc) of the solar cell. However, after thermal annealing, Jsc increases by ∼6.5 times. After thermal annealing, the GaN0.006As0.966Bi0.028 solar cells (bandgap (Eg) = 1.15 eV) exhibited an open-circuit voltage (Voc) of 0.35 V, Jsc of 10.2 mA cm−2, and fill factor of 0.56. Based on the Urbach energy of Ga(N)AsBi, the decreased crystallinity associated with the addition of N leads to poor characteristics of GaNAsBi solar cells compared with those GaAsBi solar cells.