Performance comparison of triple and tandem multijunction a-Si:H solar cells: a numerical study

The numerically simulated performances of two subcell tandem and three subcell triple amorphous silicon-based, multijunction solar cells are compared. The current-voltage characteristics are calculated using a simulation program which allows for accurate determination of single-junction or multijunction cell response under monochromatic or global AM1.5 spectrum. The validity of the solar cell model is confirmed by the excellent agreement between the simulated and measured characteristics of in-house fabricated 13.0% tandem and 13.7% triple cells with a minimum optical bandgap of 1.4 eV. It is shown that if an even narrower bandgap material of 1.3 eV were used, the triple junction device would exceed the tandem by over 1% under global AM1.5 (14.2% versus 13.2%). Assuming that both cells absorb the same amount of light, this difference is mainly due to the weaker electric fields in the double-junction cell in which the individual cell thicknesses are larger