Vertical junction high-efficiency concentrator photovoltaic cells

High concentration PV systems usually prefer tandem III-V cells to Si cells, due to the much lower conversion efficiency of the latter. We re-examine the efficiency achievable with Si Vertical Multi-Junction (VMJ) cells consisting of series-connected vertical p-n junctions within a single cell. A comprehensive 2D numerical analysis of a Si vertical junction has been performed, over a wide range of design parameters and concentration levels. The results show outstanding performance potential under high concentration of 1,000 suns and higher, with efficiencies above 29% under realistic (non-ideal) assumptions. This compares to reported efficiencies of about 20% for both real cells and previous simulations using realistic assumptions. This difference may be attributed to two effects: a better representation of the active layer photoconductivity, which lowers drastically the cell´s series resistance under high concentration; and optimization of the junction dimensions without restriction due to the accepted fabrication process.