Vertical Multi-Junction (VMJ) Silicon Solar Cells
Planar (2-D) and 3-D numerical analysis of a Si vertical junction show outstanding performance potential under high concentration of 1,000 suns and higher, with efficiencies above 29% and over 20% at one sun, under realistic (non-ideal) assumptions. The simulations are based on two possible structures that can be implemented by different monolithic processes and both indicate high performances and optimal dimensions of about 50 mm unit subcell width. Vertical junction in the planar structure can be obtained by doping through the sidewalls of vertical trenches while three dimensional arrays of radial vertical junctions and contacts can be implemented in an array of macro-pores extending from the back surface of the cell. The cell can be segmented and series connected with minimal loss of active area to provide a high-voltage, low-current device. This proposed design features the advantages of two types of solar cells: the Point-Contact (PC) cell with no shading elements at the front surface; and the Vertical Multi-Junction (VMJ) cell with high performance due to decoupling and separate optimization of optical absorption and charge collection, as well as operation at high voltage and low current. 2D Vertical multi-junction (VMJ) silicon cells array of 10 vertical junctions (VJ) serial connected provide about 5.5Vin 1 sun and 6.6V in 1200 suns.