The role of hydrogenated amorphous silicon oxide buffer layer on improving the performance of hydrogenated amorphous silicon germanium single-junction solar cells

Hydrogenated amorphous silicon oxide (a-Si1−xOx:H) film was used as a buffer layer at the p-layer (μc-Si1−xOx:H)/i-layer (a-Si1−xGex:H) interface for a narrow band gap hydrogenated amorphous silicon germanium (a-Si1−xGex:H) single-junction solar cell. The a-Si1−xOx:H film was deposited by plasma enhanced chemical vapor deposition (PECVD) at 40 MHz in a same processing chamber as depositing the p-type layer. An optimization of the thickness of the a-Si1−xOx:H buffer layer and the CO2/SiH4 ratio was performed in the fabrication of the a-Si1−xGex:H single junction solar cells. By using the wide band gap a-Si1−xOx:H buffer layer with optimum thickness and CO2/SiH4 ratio, the solar cells showed an improvement in the open-circuit voltage (Voc), fill factor (FF), and short circuit current density (Jsc), compared with the solar cells fabricated using the conventional a-Si:H buffer layer. The experimental results indicated the excellent potential of the wide-gap a-Si1−xOx:H buffer layers for narrow band gap a-Si1−xGex:H single junction solar cells.