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

Abstract

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 µm 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. ΔEC:ΔEV) is set to 0.65:0.35. While efficiency remains approximately constant with moderate n-doping (up to 5 × 1016 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 × 10−3 °C−1), −0.09 (−0.95 × 10−3 °C−1) and −0.2 (−2.38 × 10−3 °C−1)%/°C for single heterojunction (SHJ), double-heterojunction (DHJ) and tandem-graded design is predicted from the numerical simulations.