We investigate that 1,4,5,8-napthalene-tetracarboxylic-dianhydride (NTCDA)/3,4,9,0perylenetetracarboxylicbisbenzimidazole(PTCBI) bilayer buffer layer can impro ve the performance of Rubrene/C₇₀-based small molecule organic solar cells (OSCs) with the s tructure of ITO/MoO₃/Rubrene/C₇₀/NTCDA/PTCBI/Al.The results show that the performanc e of devices is significantly improved with the bilayer buffer layer.When the op timum thickness of PTCBI layer is 5nm,the performance parameters of the device are the best with power convers ion efficiency (PCE) of 3.19%,short-circuit current den sity (Jsc) of 8.99mA·cm－2,open-circuit v oltage (Voc) of 0.85V and fill factor (FF) of 41.58%,respectively.Compared w ith devices without PTCBI layer,the improvements of the above parameters are 3538%,338.5%,13.3% and 16.5%,respectively.