Optimal design of amorphous/crystalline tandem cells

Computer analysis has been used to determine the conversion efficiency of amorphous-on-crystalline and crystalline-on-amorphous two-cell tandem structures as a function of the energy gaps of the component cells. Four-terminal (separately connected) structures have higher efficiencies than two-terminal (series-connected) structures and are less sensitive to variations in energy gap, operating temperature and air mass. The optimal amorphous/crystalline tandem structures show only a modest increase in efficiency over their component crystalline cells. Unless the production costs of the tandem structures are low, this increase may not be sufficient to justify their adoption.