The interface modification between the organic active layer and the inorganic electrode affects the performance of organic solar cell (OSC). A buffer layer of alkylthiol(ethanethiol, hexanethiol, dodecanethiol) /Au self-assembly layer was introduced into OSC to substitute Poly(3,4-ethylenedioxythiophene)∶poly(styrene sulfonate) (PEDOT∶PSS) layer, in order to improve the organic/inorganic interface. We fabricated devices with structure of “ITO/Au (annealed Au film of 2 nm)-thiol self assembly layer/ poly(3-hexylthiophene)∶1-(3-methoxycarbonyl) -propyl-1-phenyl-(6,6)C61(P3HT∶PCBM) /LiF/Al”. After alkanethiol self-assembling, the alkanethiol prevented exciton quenching owe to direct contact between the Au NPs and the active layer.We studied the impact of alkanethiol with different chain length on device performance. With?the?growth?of?the?alkyl chain, the coverage of the thiol on Au NPs got better, and the device performance become better. In the OSC with dodecanethiol /Au (2 nm Au film annealed) self-assembly film, the short-circuit current increases from 5.19 mA·cm-2 to 6.24 mA·cm-2.