Impact of Band-Gap Graded Intrinsic Layer on Single-Junction Band-Gap Tailored Solar Cells

The work investigates the performance of intrinsic layers with and without band-gap tailoring in single-junction amorphous silicon-based photovoltaic cells. The work proposes single-junction amorphous silicon solar cells in which band-gap grading has been done between layers as well as within each layer for the first time. The samples of hydrogenated amorphous silicon-germanium with different mole fractions are fabricated, and their band-gaps are validated through optical characterization and material characterization. A single-junction solar cell with an intrinsic layer made up of hydrogenated amorphous silicon (aSi:H) having a band-gap of 1.6 eV is replaced by continuously graded hydrogenated amorphous silicon-germanium (aSi1-xGe x :H ) intrinsic bottom layers having band-gaps ranging from 0.9 eV to 1.5 eV. The proposed structure has been considered as a variant of previously designed single-junction band-gap tailored structures. The suitable utilization of band-gap tailoring on the intrinsic absorber layer aids more incident photons in energy conversion and thereby attain a better short circuit current density of 19.89 mA/cm2. A comparative study on performance parameters of solar cell structures with graded band-gap intrinsic layer and the ungraded single band-gap intrinsic layer has been done. The graded band-gap intrinsic layer structure results in better conversion efficiency of 15.55%, while its ungraded counterpart contributes only 14.76 %. Further, the proposed solar structure is compared with the performance parameters of recent related works. The layers used in the proposed solar structure are of amorphous-phase only, which reduces structural complexity. The use of a lesser number of active layers reduces the number of fabrication steps and manufacturing cost compared to state-of-the-art.