During the past two years, the introduction of DMSO has revolutionized the fabrication of high-quality pervoskite MAPbI3 (MA = CH3NH3) films for solar cell applications. In the developed DMSO process, the formation of (MA)2Pb3I8·2DMSO (shorted as Pb3I8) has well recognized as a critical factor to prepare high-quality pervoskite films and thus accomplish excellent performances in perovskite solar cells. However, Pb3I8 is an I-deficient intermediate and must further react with methylammonium iodide (MAI) to be fully converted into MAPbI3. By capturing and solving the molecular structures of several intermediates involved in the fabrication of perovskite films, we report in this work that the importance of DMSO is NOT due to the formation of Pb3I8. The use of different PbI2-DMSO ratios leads to two different structures of PbI2-DMSO precursors (PbI2·DMSO and PbI2·2DMSO), thus dramatically influencing the quality of fabricated perovskite films. However, such an influence can be minimized when the PbI2-DMSO precursor films are thermally treated to create mesoporous PbI2 films before reacting with MAI. Such a development makes the fabrication of high-quality pervoskite films highly reproducible without the need to precisely control the PbI2:DMSO ratio. Moreover, the formation of ionic compound (MA)4PbI6 is observed when excess MAI is used in the preparation of perovskite film. This I-rich phase heavily induces the hysteresis in PSCs, but is readily removed by isopropanol treatment. On the basis of all these findings, we develop a new effective protocol to fabricate high-performance PSCs. In the new protocol, high-quality perovskite films are prepared by simply treating the mesoporous PbI2 films (made from PbI2-DMSO precursors) with an isopropanol solution of MAI, followed by isopropanol washing. The best efficiency of fabricated MAPbI3 PSCs is up to 19.0%. As compared to the previously reported DMSO method, the devices fabricated by the method reported in this work display narrow efficiency distributions in both forward and reverse scans. And the efficiency difference between forward and reverse scans is much smaller.

Perovskite solar cells (PSCs) have been demonstrated as one of the most promising candidates for solar energy harvesting. Here, for the first time, a functionalized nanographene (perthiolated trisulfur-annulated hexa-peri-hexabenzocoronene, TSHBC) is employed as the hole transporting material (HTM) in PSCs to achieve efficient charge extraction from perovskite, yielding the best efficiency of 12.8% in pristine form. The efficiency is readily improved up to 14.0% by doping with graphene sheets into TSHBC to enhance the charge transfer. By the HOMO-LUMO level engineering of TSHBC homologues, we demonstrate that the HOMO levels are critical for the performance of PSCs. Moreover, beneficial from the hydrophobic nature of TSHBC, the devices show the improved stability under AM 1.5 illumination in the humidity about 45% without encapsulation. These findings open the opportunities for efficient HTMs based on the functionalized nanographenes utilizing the strong interactions of their functional groups with perovskite.

In the field of photovoltaic industry, organolead halide perovskite solar cells (PSCs) as cleaner and cheaper photo‐voltaic devices have shown a bright prospect with power conversion efficiency (PCE) rapidly climbing from 3.8% to certified 22.1% in a few years. Interface engineering has been proven to be highly effective to solve the instability‐to‐moisture issue and enhance the performance of PSCs. Here, this work develops a simple and easy‐proceeding strategy that depositing both aminocaproic acid [H2NCH2(CH2)4COOH, abbreviated as AmCA] and caproic acid [CH3(CH2)4COOH, CA] at the mesoporous TiO2/perovskite interface leads to significant enhancement in both the efficiency and stability of PSCs. These two organic modifiers work synergistically to enhance the overall performance of PSCs by promoting electron transfer through the interaction between amino groups on AmCA and perovskite layer, and resisting moisture with alkyl chains from CA. The champion efficiency of modified cells reaches 18.2%, with an average PCE of 17.5% in reliable reproducibility, with significant improvement in stability under 50 ± 5% relative humidity in air. The developed simple interfacial modification approach should be effective to enhance both efficiency and stability of PSCs with other architectures as well. More importantly, this scenario may provide insight into the commercialization of perovskite solar cells in the not‐too‐distant future.

N-Methyl-2-pyrrolidone (NMP), forming only one PbI2·NMP complex, is demonstrated as an excellent coordinative solvent for the fabrication of high-quality perovskite thin films.