Microscopic investigation of the CdS buffer layer growth on Cu(In,Ga)Se₂ absorbers

To obtain highly efficient thin film solar cell devices, a thin buffer layer of CdS is deposited onto a Cu(In,Ga)Se₂ absorber layer. Here, the authors report a photoemission electron microscopy study investigating the growth of evaporated CdS buffer layers. For thin CdS layers (≪1 nm thickness), they observed enhanced CdS growth on some grains, while other grains remain uncovered or only weakly covered. For thicker CdS layers, they observed a more homogeneous growth. After annealing these layers, an increase in the detailed In and Se structure is observed as well as the reappearance of the inhomogeneous Cd distribution. This indicates an intermixing of CdS and Cu(In,Ga)Se₂. The influence of such interdiffusion on solar cell efficiency is discussed.