Diminished band discontinuity at the p/i interface of narrow-gap a-SiGe:H solar cell by hydrogenated amorphous silicon oxide buffer layer

Highlights: • a-SiO_x:H buffer layer played significant role in band discontinuity balance. • V_oc enhancement by 3.7% due to optoelectronic optimization of a-SiO_x:H buffers. • High efficiency of 9.6% of narrow-gap a-SiGe:H solar cell with high V_oc of 0.82 V. We optimized hydrogenated amorphous silicon oxide (a-SiO_x:H) as a buffer layer at the p/i interface of hydrogenated amorphous silicon germanium (a-SiGe:H) solar cells. This buffer layer was intended to effectively diminish the band discontinuity between the high-bandgap p-window layer and low-gap a-SiGe:H absorption layer, thereby enhancing the cell performance. The open-circuit voltage (V_oc) increased by 3.7% as the [CO₂]/[SiH₄] gas ratio increased from 0 to 0.06. In addition, the short-circuit current density (J_sc) gradually increased with the gas ratio. Using the optimized a-SiO_x:H buffer layer, a high performance of 9.6% was recorded for narrow-gap a-SiGe:H thin film solar cells. a-SiGe:H solar cells with optimized a-SiO_x:H buffer layers, used as middle subcells, are expected to enhance the total V_oc of triple-junction configuration solar cells.