The exceptional optical and electronic properties of graphene make it a promising material for photodetection, especially applications requiring fast and sensitive response to light across the spectrum ranging from the visible to the infrared down to the terahertz domain. However, the ultrashort lifetime of photocarriers caused by the fast recombination of graphene results in the weak response of light and limits its application in photodetection. To overcome the restriction of limited lifetime of photocarriers in photodetection, it is necessary to introduce graphene p-n junctions to generate photocurrent or photovoltage efficiently, and numerous efforts have been made. In this review, we first give an overview of photodetection and then evaluate physical and chemical methods available for the fabrication of graphene p-n junctions. Subsequently, we provide a detailed discussion on current research advances in enhancing the performance of graphene-based photodetectors, mainly focusing on the coupling of graphene with photonic structures and building vertical heterostructures. We believe that the potential commercialization of graphene p-n junction based photodetectors will be promoted by the development on the scalable production of graphene and its integration with highly developed silicon-based photonic and electronic platforms. (C) 2015 Elsevier Ltd. All rights reserved.