  Superconducting and normal state transport properties in iron pnictides are
sensitive to disorder and impurity scattering. By investigation of
Ba(Fe1-xCox)2As2 thin films with varying Co concentration, we demonstrate that
in the dirty limit the superconducting dome in the electronic phase diagram of
Ba(Fe1-xCox)2As2 shifts towards lower doping concentrations, which differs
significantly from observations in single crystals. We show that especially in
the underdoped regime superconducting transition temperatures higher than 27 K
are possible.
