In which layer of the sun is energy transferred between atoms

The answer is core.
 
 Intense heat that destroys the internal structure of an atom and therefore all atom are broken down in its constituent parts, happens in the core. Core is the source of sun's energy and the innermost layer of the sun. Thermonuclear reaction takes place, hydrogen atoms are combined to make helium atoms and produces energy that keeps the sun in its equilibrium state. Thermonuclear reaction is  called nuclear fusion.