•The surface ageing of PEDOT:PSS has been studied during 6 months.•Impact of temperature, cross-linker concentration and storage conditions have been monitored.•The interface undergoes significant reorganization regardless of the concentration of cross-linker.•The temperature (37 °C) induces irreversible changes in the composition of film even in presence of cross-linker.•Pristine and cross-linked polymers need two to four months to stabilize their interface. Known for its electric properties, poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) has emerged as a good candidate for organic electronics and more recently for bio-applications. Despite its growing use in engineering applications, little is known about the stability in time of its interface properties. Here, we consider the surface ageing of PEDOT:PSS when it is stored in environments with various relative humidity and temperature conditions and as a function of the cross-linking agent’s (3-glycidoxypropyltrimethoxysilane) concentration. Our systematic wettability study over 6 months reveals that the PEDOT:PSS interface undergoes significant reorganization and some irreversible changes on these timescales regardless of the concentration of cross-linker added.