High performance and durable electrodes are prerequisites for the stable operation of various optoelectronic devices, such as alternating current electroluminescence (ACEL) applications. As for the flexible electrodes based on ultrathin metals, which have attracted much attention in recent years, stability problems as evidenced by optically lossy and electrical degradation of the silver (Ag) layer in the service environment are the key issues to be solved before its practical application. This work prepares ultrathin and stable doped silver films by introducing a small amount of AlN during the sputtering process. The Ag-AlN thin films exhibit a comprehensive stability promotion in terms of high temperature (250 °C in the air) and damp-heat (85 °C, 85% relative humidity (RH) for 12 h) test compared with pure Ag counterpart. In addition, flexible ACEL devices based on AZO/Ag-AlN/AZO/polyethylene terephthalate (PET) films with a luminance of 176.1 cd m−2 at 300 V and 400 Hz and excellent luminescence performance and mechanical flexibility under operating conditions are developed. Such ACEL devices based on these ultrathin and durable Ag-AlN films are up-and-coming in practical, flexible electronics applications.