Poly(ethylene oxide) (PEO)-based solid polymer electrolyte films with NaYF4 and NaYF4+plasticizer (dimethyl formamide) have been prepared by the solution-cast technique. Various experimental techniques have been used, such as electrical conductivity (composition dependence, temperature dependence in the temperature range 303-400 K) and transport number measurements, to characterise these polymer electrolyte films. The conductivity-temperature plots showed an increase in conductivity with increasing temperature. The increase in conductivity is about 10 times larger in the plasticizer-added (PEO + NaYF4) polymer electrolyte system compared with the pure (PEO + NaYF4) polymer electrolyte system. Electrochemical cells of configuration Na/(PEO + NaYF4 + plasticizer)/(I-2 + C + electrolyte) have been fabricated. The discharge characteristics of the cells were studied for a constant load of 100 k Omega. The open circuit voltage (OCV), short circuit current (SCC), discharge time for the plateau region, etc., were evaluated and compared with data from our earlier reported (PEO + NaYF4) electrochemical cells.