Numerical Modeling of Silicon Nanocrystal Down-Shifting Layers for Enhanced CIGS Solar Cell Performance

The performance effects of silicon nanocrystals (SiNC) embedded in a silicon dioxide matrix to act as a downshifting (DS) layer mounted on the top surface of a polycrystalline Cu(In,Ga)Se2 solar cell are explored numerically. The DS layers are modeled by modifying the incident AM1.5G spectrum based on the absorption and emission properties of the SiNC. The effects of the DS layers as an anti-reflection coating leads to an 11.4% relative improvement in short-circuit current density under J-sun illumination $(0.1\ {\rm W}/{\rm cm}^{2})$. Comparatively, the effect of down-shifting high-energy photons to lower energy photons showed a 4% relative short-circuit current density improvement, albeit for an optical conversion efficiency of 80%.