A computer analysis of heterojunction and graded composition solar cells

The development and application of a variable composition solar cell computer analysis program is discussed, The basic device equations as used in the computer analysis are derived and the techniques used to model material parameter variations described. Finally, the results of the computer analysis of several Al
x
Ga
1-x
As and GaAs
1-x
P
x
solar cell structures are presented along with a discussion of the effects of interface states and various composition and doping profiles on maximum solar cell efficiency. Interface states are found to be responsible for a severe reduction in the efficiency of GaAs
1-x
P
x
cells, but do not significantly affect the behavior of Al
x
Ga
1-x
As cells. The depth of the p-n junction below the wide bandgap window layer is a critical factor in determining the loss of minority carriers to interface recombination at the heterojunction.