A review on n-type chemical doping of graphene films: preparation, characterization and applications

Chemical doping has emerged as a powerful approach for modulating the electronic properties of graphene, and particularly for enabling its integration into advanced electronic and optoelectronic devices. While considerable progress has been made in achieving stable p-type doping, realizing efficient and reliable n-type doping remains a greater challenge due to the inherent instability of most electron-donating dopants and intrinsic semi-metallic nature of pristine graphene. This review summarises the recent developments in n-type chemical doping of graphene films, with a primary focus on substitutional doping and surface charge transfer mechanisms. The discussion covers the preparation strategies, including in situ and post-treatment doping using various dopants, namely nitrogen, phosphorus, sulfur, metals, and molecular species. Subsequently, the influence of precursor chemistry, chemical vapor deposition (CVD) parameters, and interface engineering on doping efficiency and stability is highlighted. In parallel, advanced characterization techniques are surveyed, with emphasis on their capability to probe bonding configuration, electronic structure, and local dopant distribution. Finally, potential applications of n-doped graphene films in high-performance field-effect transistors, transparent electrodes, and flexible sensors are outlined. The review also discusses current challenges and perspectives on future research directions, including atomically precise doping control, multi-modal characterization, and the exploration of synergistic doping strategies for scalable and stable device integration.