A TCAD-based modeling of GaN/InGaN/Si solar cells

Theoretical efficiency potential of GaN/InGaN/cSi tandem solar cells is investigated using two-dimensional numerical computer simulation (i.e. technology-based computer aided design tool: TCAD). With double-junction GaN/InGaN/cSi tandem design, a conversion efficiency of 27% is achieved using a 1.0 mu m In0.5Ga0.5N absorber of top cell over crystalline silicon (cSi) bottom cell. This efficiency is further improved to 29.0% with grading of the InxGa1-xN absorber layer close to the top heterointerface (p(+)-GaN/n(-)-InxGa1-xN) of the solar cell. A maximum conversion efficiency is obtained when the band discontinuity ratio (i.e. Delta E-C:Delta E-V) is set to 0.65:0.35. While efficiency remains approximately constant with moderate n-doping (up to 5 x 10(16) cm(-3)) in the top InGaN absorber layer, sensitivity of the efficiency to the interface trap density and trap cross-section (when traps are located only at the heterointerfaces) shows degraded behavior with increasing trap density and trap cross-section. A temperature coefficient for open-circuit voltage (efficiency) of -0.15 (-1.72 x 10(-3) degrees C-1), -0.09 (-0.95 x 10(-3) degrees C-1) and -0.2 (-2.38 x 10(-3) degrees C-1)%/degrees C for single heterojunction (SHJ), double-heterojunction (DHJ) and tandem-graded design is predicted from the numerical simulations.