Analysis of an edge-illuminated graded-gap solar cell

It has been established that even under ideal conditions the efficiency of a semiconductor photovoltaic cell with a single energy gap cannot exceed approximately 30%. One possible configuration for avoiding this limitation is the edge-illuminated graded-gap solar cell, in which the plane of the p-n junction is parallel to the incident radiation and the gap is graded from a larger value at the illuminated surface to a smaller at the back. Calculations were carried out for (a) fixed front-surface energy gap and variable backsurface gap, and (b) fixed back-surface gap and variable front-surface gap. In each case the fixed gap was 1.47 eV. The best result was an increase of theoretical efficiency from 27.2 to 28.3% for the first case with a back surface gap of l.27eV at a thousand suns. To increase the efficiency further it would be necessary to segment the device.