The easy oxidation and surface roughness of Cu nanowire (NW) films are the main bottlenecks for their usage in transparent conductive electrodes (TCEs). Herein, we have developed a facile and scaled-up solution route to prepare Cu NW-based TCEs by embedding Cu NWs into pre-coated smooth poly(3, 4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) films on poly(ethylene terephthalate) (PET) substrates. The so obtained Cu NW-PEDOT: PSS/PET films have low surface roughness (~70 nm in height), high stability toward oxidation and good flexibility. The optimal TCEs show a typical sheet resistance of 15 Ω·sq^-1 at high transparency (76% at λ = 550 nm) and have been used successfully to make polymer (poly(3-hexylthiophene): phenyl-C61-butyric acid methyl ester) solar cells, giving an efficiency of 1.4%. The overall properties of Cu NW-PEDOT: PSS/PET films demonstrate their potential application as a replacement for indium tin oxide in flexible solar cells.