Polymer bulk-heterojunction solar cells with poly(ethylene oxide)(PEO) as cathode interfacial layer,and P3HT:PCBM as active layer are prepared.The effect of the PEO layer′s thickness on the performance of polymer solar cells and the degradation characteristics of this system are investigated.The stabilities of the device with PEO interfacial layer and the control device are copared.The differences of the resistances between the device with PEO interfacial layer and the control device are studied...