Identifying the Molecular Structures of Intermediates for Optimizing the Fabrication of High-Quality Perovskite Films

Abstract

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.

Effects of Iodine Doping on Carrier Behavior at the Interface of Perovskite Crystals: Efficiency and Stability

“…Meanwhile, an additional peak emerged at 6.79 • after one week in air. This peak was compared with related research [30]. A new phase of the Pb 3 I 8 intermediate was formed due to the perovskite decomposition.…”

Function Follows Form: Correlation between the Growth and Local Emission of Perovskite Structures and the Performance of Solar Cells

“…Using a mixture of solvents (DMF + DMSO) for the preparation of CH(NH 2 ) 2 PbBr 3 films, the preferred crystal orientation vanishes and we obtain a nearly isotropic angular distribution ( Figure S9). [40] From CL analysis, we conclude that the smooth CH(NH 2 ) 2 PbBr 3 films shows isotropic distribution of cathodoluminescence, whereas large and oriented CH(NH 2 ) 2 PbBr 3 crystals exhibit highly non-uniform emission. Such variations in the photophysical properties establish that the nature of the solvent employed for the deposition of the perovskite films is an important parameter.…”

In Situ Real‐Time Study of the Dynamic Formation and Conversion Processes of Metal Halide Perovskite Films

“…[1,6,7,[17][18][19] Among them, the method involving the formation of intermediate adduct (IA) phases is extremely effective in fabricating highly uniform and dense perovskite films that deliver high-efficiency PSC devices. [5,20] So far, this method is regarded as one of the most successful ways to fabricate the state-of-the-art PSC devices. It is plausible that the intermediate phase retards the rapid formation of perovskite species and thus effectively regulates perovskite crystal growth.…”