▎ 摘　　要

A simple method for synthesizing a series of graphene oxide with precise oxidation (pr-GO) (mild oxidation, moderate oxidation and severe oxidation) by strictly controlling pre-oxidation steps, oxidant content and oxidation time has been successfully developed. The well defined pr-GO as hole extraction layer (HEL) presented multiple functionalities, like modulation of work function, enhanced interfacial dipole, and excellent film-forming properties, which had significantly improved the efficiency and stability of organic solar cells. The P3HT:PC61BM system device based on pr-GO-3 HEL, which possessing well defined electronic structure and moderate oxidation, exhibited an improved 3.74% in power conversion efficiency and better air-stability compared to that of other pr-GOs and conventional PEDOT:PSS based devices. The well defined electronic structure pr-GO (i.e., suitable work function, larger interfacial dipole, and high repeatability) will provide better understanding in utilizing pr-GO film as HEL in future solar cell applications. (C) 2014 Elsevier B.V. All rights reserved.