PROJECT TITLE :

Compositional Gradients in Cu(In,Ga)Se$_$ Thin Films for Solar Cells and Their Effects on Structural Defects

ABSTRACT:

Cu(In,Ga)Se$_2$ (CIGSe) absorber layers utilized in thin-film solar cells exhibit, when grown in a multistage method, compositional gradients of Ga and In. During this study, the correlations between the Ga gradient and the microstructure are studied by means that of transmission electron microscopy (TEM) imaging combined with energy-dispersive X-ray spectroscopy (EDX), allowing the determination of structural defects and elemental distributions at identical sample positions. The prevalence of linear defects (dislocations) and planar defects (stacking faults and microtwins) of CIGSe layers was studied by means of TEM pictures. The Ga distributions obtained from EDX elemental distribution maps and structural parameters from the literature were used to calculate the lattice parameters c and a and also the gradient dc/ dx perpendicular to the substrate. We found a correlation between the magnitude of dc/dx and also the prevalence of dislocations among individual massive grains. From the presented results, a threshold worth of the Ga gradient of 12–13at.%/μm will be estimated for the formation of misfit dislocations.