This paper introduces the methods improving the performance and stability of copper-phthalocyanine(CuPc)/ fullerene(C60) small molecule solar cells by using tris-(8-hydroxyquinoline)aluminum(Alq3): cesium fluoride(CsF) composite cathode buffer layer. The device with Alq3∶CsF composite cathode buffer layer with a 4 wt.% CsF at a thickness of 5 nm exhibits a power conversion efficiency (PCE) of up to 0.76%, which is an improvement of 49%, compared to a device with single Alq3 cathode buffer layer and half-lifetime of the cell in air at ambient circumstance without any encapsulation is almost 9.8 hours, 6 times higher than that of without buffer layer, so the stability is maintained. The main reason of the device performance improvement is that doping of CsF can adjust the interface energy alignment, optimize the electronic transmission characteristics of Alq3 and improve the short circuit current and the fill factor of the device using ultraviolet-visible absorption, external quantum efficiency and single-electron devices. Placed composite cathode buffer layer devices with different time in the air, by comparing and analyzing current voltage curve, Alq3∶CsF can maintain a good stability as Alq3. Alq3∶CsF layer can block the diffusion of oxygen and moisture so completely as to improve the lifetime of the device.