The deposition of intrinsic hydrogenated amorphous silicon thin films incorporated with oxygen by plasma-enhanced vapor deposition

Intrinsic hydrogenated amorphous silicon films incorporated with oxygen (i a-Si(H,O):H) were prepared using a plasma-enhanced chemical vapor deposition system with a carbon dioxide (CO₂), silane (SiH₄) and hydrogen (H₂) gas mixture. The influence of oxygen incorporation on the chemical structure and on the optoelectronic properties of the deposited films was investigated. The performance of the solar cells that use these films as absorber layers was also evaluated. For the films incorporated with oxygen, local bonding configurations were identified in which H and O alloy atoms were bonded to the same Si site. With the incorporation of oxygen, the bandgap (E_opt) of the a-Si(H,O):H films increased significantly to 1.82 eV, while that of the pure hydrogenated amorphous (a-Si:H) films was 1.73 eV. The optoelectronic properties of the oxygen-incorporated films degraded due to the newly created dangling bonds that arose from an increased structural disorder. Increasing the hydrogen dilution in the plasma effectively reduced the defect density in the a-Si(H,O):H films, resulting in an improved photosensitivity. The solar cells that used wide-bandgap a-Si(H,O):H films as absorber layers exhibited a 26.3% higher open circuit voltage (V_oc) than those that used pure a-Si:H films, mainly because of the increased E_opt of the films and the reduced defect density that was due to a high hydrogen dilution.