Keyou Yan, Zhanhua Wei, Jinkai Li, Haining Chen, Ya Yi, Xiaoli Zheng, Xia Long, Zilong Wang, Jiannong Wang, Jianbin Xu, and Shihe Yang* cell performance degraded quickly due probably to chemical etching of Au by iodide. Therefore, carbon electrodes, a chemically and thermally stable material, such as 0D carbon black, candle soot, and 1D carbon nanotube, were also employed to serve as low cost hole extraction electrode due to their suitable Fermi level at≈− 5.0 eV, and to eliminate both the HTM layer and the vacuum-deposited noble metal electrode.[9, 10] At the same time, we employed candle soot electrode as a hole extractor to achieve 2% PCE at first and then 11% after chemical modification of the interface between perovskite and carbon electrode, making a key step toward metal electrode-free PSC.[11] Compared to HTM based PSC, carbon electrode displayed outstanding long-term performance stability when operating for more than 1000 h under illumination, demonstrating commercial potential.[10] To date, however, the nature of the interface between perovskite and nanocarbon hole extraction electrodes has not been addressed and until now, the fill factor (FF) of carbon based PSC was still less than 0.70.[10] In this work, we employ flexible reduced graphene oxide [12] to yield conducting graphene as hole extraction electrode. Single-layered graphene (SG) and multilayered graphene (MG) are employed in the solar cells, which actually have different work functions (4.8 eV for SG and 5.0 eV for MG). This energetic difference will result in ohmic contact (SG/perovskite) and Schottky junction (MG/perovskite) with perovskite (Fermi level at− 4.73 eV) if well-assembled, and will help to find out the suitable interfacial contact regime for hole extraction and charge separation. The assembly of graphene toward final perovskite is realized by the chemically reactive paste made of graphene and CH 3NH 3I, which can release the organic component of CH 3NH 3I to PbI 2 at the interface between graphene and PbI 2 and transform PbI 2 to CH 3NH 3PbI 3 perovskite to reduce pinholes,[11, 13, 14] thereby yielding a perfect contact for efficient hole extraction. Indeed, MG/perovskite interface was successfully assembled as a Schottky junction, with a rectifying characteristic, which afford hole extraction and electron rejection effectively, whereas the SG/perovskite interface shows an ohmic contact behavior, whose chargeselective capability is not nearly as well as MG. This is confirmed by time resolved photoluminescence (TRPL), which shows that MG has higher hole extraction rates (5.1 ns− 1) than SG (< 3.7 ns− 1). MG is a champion for hole extraction,