DOI: 10.1002/adma. 201604695 temperature and solution-processed methods for each layer of PVSCs are highly desirable. While there is a very limited study in room-temperature solution-processed PVSCs and only an nip planar structure of ZnO/CH3NH3PbI3/spiro-OMeTAD has been reported with power conversion efficiency (PCE) of 15.7% on glass substrate,[35] its device stability is still a concern such as the potential reaction between ZnO and perovskite.[36] Up to now, it is still challenging to fabricate room-temperature solution-processed PVSCs with high performance and good stability.

The growth of perovskite film is a critical step to produce high efficiency and stable PVSCs.[2, 4–9, 12–20, 29] Considering CH3NH3PbI3-based PVSCs, the two-step dipping deposition provides an efficient and low-cost route toward large-scale production of PVSCs.[5, 6, 31] However, when PbI2 is deposited on a flat substrate, it tends to form a layered and dense film. Therefore, there is a concern of uncompleted conversion of PbI2 to perovskite during the exposure to CH3NH3I solution in a short time. The unreacted PbI2 in the final device will reduce photovoltaic performances and stability.[5] While prolonging the reaction time seems to be a good method to address this issue, the dissolution and incontrollable morphology of perovskites are detrimental to the device performances. These drawbacks make it difficult to fabricate scalable planar PVSCs by a conventional sequential deposition method. Although thermal annealing is an effective tool to accelerate the conversion of PbI2 into perovskite,[32–34] layer-dependent fabrication complexity and energy consumption may hinder upscaling of the PVSCs.[31] Although other ligands (eg, dimethyl sulfoxide, 4-tert-butylpyridine and N-methyl-2-pyrrolidone) have been reported to control the crystallization of perovskite by forming PbI2.(ligand) x or CH3NH3I-ligand-PbI2 intermediates,[5, 37] high-temperature thermal annealing (≥ 100 C) is required to remove the ligands for forming high-quality perovskites. In this work, we propose a new scheme of pyridine (Py)-promoted formation of high-quality perovskite films at room temperature for the first time. In addition, we demonstrate the approach of employing an all room-temperature solution process to fabricate the pin planar structure of NiOx/CH3NH3PbI3/C60 for achieving high performance and stable PVSCs. Our results show that room-temperature-processed PVSCs with PCE reaching 17.10% on indium tin oxide (ITO) coated glass substrate are achieved, which is the best results for PVSCs fabricated by all room-temperature solutionprocessed techniques to date. In addition, our all room-temperature solution-processed technique enables the fabrication of