Graded Layer Modification for High Efficiency Hydrogenated Amorphous Silicon–Germanium Solar Cells

Abstract

Hydrogenated amorphous silicon–germanium (a-SiGe:H) solar cells are fabricated with different thicknesses of the i/n graded layer and profiling shapes for appropriate band gap profiling. Comparison of the solar parameters between the U-shape profiling and the exponential shape (E-shape) profiling has been carried out at the same total thickness. In the U-shape profiling, as the thickness of the i/n graded layer increase, the fill factor (FF) and open circuit voltage (Voc) of p–i–n single-junction a-SiGe:H solar cells increase, but the short circuit current (Jsc) of cells decreases. In the E-shape profiling, the Jsc of the a-SiGe:H cell is enhanced without significant losses in Voc. For further analysis, a modified E-shape profiling is incorporated in a-Si:H/a-SiGe:H double-junction cells, which has resulted in the improvement of Voc and FF of double-junction cells to 1.67 V and 0.753, respectively, without significant reduction in JscSiGeQE, 12.58 mA/cm2.