▎ 摘　　要

The long-term stability of methylammonium lead triiodide (MAPbI(3)) perovskite in moist environments is a paramount challenge to realise the commercialization of perovskite solar cells. In an attempt to address this concern, we have carried out systematic first-principles studies on the MAPbI(3) perovskite with a hydrophobic graphene layer interfaced as a water barrier. We find there is a charge transfer at the graphene/MAPbI(3) interface and electrons can be excited from graphene into the perovskite surface, leading to well separated electron-hole pairs, i.e. reduced recombination. By studying the optical properties, we find the hybrid graphene/MAPbI(3) nanocomposite displays enhanced light absorption compared with the pristine MAPbI(3). Furthermore, from an ab initio molecular dynamics simulation, the graphene/MAPbI(3) nanocomposite is confirmed to be able to resist the reaction with water molecules, highlighting a great advantage of this nanocomposite in promoting long-term photovoltaic performance.