Efficiency enhancement in Cu2ZnSnS4 solar cells with silica nanoparticles embedded in absorber layer

Light trapping is essential to lower transmission losses in thin-film solar cells, particularly for wavelengths where the absorption is inefficient. We have embedded silica nanoparticles into a CZTS absorber layer resulting in localized as well as scattering field enhancement. UV-Vis absorption measurements show position (depth in the absorber layer) dependent improvement in the optical absorption with incorporation of silica nanoparticles; this has been explained using finite-difference-time-domain (FDTD) calculations of Mie scattering. The optical enhancement in turn leads to efficiency improvement as seen from electrical measurements; this has a slightly different position dependence that can also be understood theoretically. We observe maximal efficiency improvement, of about 21% compared to devices without nanoparticles (reference cell efficiency ~ 4.13% and for particles at middle ~ 5%), when nanoparticles are placed at the middle of the absorber layer.