Temperature-Dependent Crystallization Mechanisms of Methylammonium Lead Iodide Perovskite From Different Solvents

Abstract

Hybrid perovskites are a novel type of semiconductors that show great potential for solution-processed optoelectronic devices. For all applications, the device performance is determined by the quality of the solution-processed perovskite thin films. During solution processing, the interaction of solvent with precursor molecules often leads to the formation of solvate intermediate phases that may diverge the crystallization pathway from simple solvent evaporation to a multi-step formation process. We here investigate the crystallization of methylammonium lead iodide (MAPbI3) from a range of commonly utilized solvents, namely dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and gamma-butyrolactone (GBL) at different temperatures ranging from 40°C to >100°C by in-situ grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements. For all solvents but GBL, we clearly observe the formation of solvate-intermediate phases at moderate processing temperatures. With increasing temperatures, an increasing fraction of the MAPbI3 perovskite phase is observed to form directly. From the temperature-dependence of the phase-formation and phase-decomposition rates, the activation energy to form the MAPbI3 perovskite phase from the solvate-phases are determined as a quantitative metric for the binding strength of the solvent within the solvate-intermediate phases and we observe a trend of DMSO > DMF > NMP > GBL. These results enable prediction of processing temperatures at which solvent molecules can be effectively removed.

Selection of a Suitable Solvent Additive for 2-Methoxyethanol-Based Antisolvent-Free Perovskite Film Fabrication

“…Similarly, as the concentration of NMP increased, the MAPbI 3 (110) peak intensity decreased in the XRD patterns while, simultaneously, the intermediate phase peak intensity increased at 8.2°. 39,40,42,43 Thus, the intermediate phase/MAPbI 3 (110) phase ratio is more clearly dependent on the amount of added NMP rather than on the ratio of the DMAc series (Figure 4b,c and Figure S12). This is presumably because the vapor pressure of NMP is lower than that of DMAc so that the residual amount of NMP in the asdeposited films increased as the amount added increased.…”

“…By comparing the XRD patterns of the pristine and DMSO-assisted films, we observed intermediate phase peaks at 6.5, 7.7, and 9.2° attributed to the (002), (021), and (022) planes of MA 2 Pb 3 I 8 (DMSO) 2 − in the XRD pattern of the as-deposited DMSO-0.2 film, indicating that the additive and the precursor were coordinated (Figure a). However, the SEM image of the DMSO-0.2 film showed pinholes on the surface of and inside the film, similar to the pristine film, unlike in previous studies , in which uniform films were obtained by adding DMSO (Figure b).…”

In Situ and Operando Characterizations of Metal Halide Perovskite and Solar Cells: Insights from Lab-Sized Devices to Upscaling Processes

“…The direct formation of MHP was observed for fast solvent removal at higher processing temperatures, as was observed in other works. The activation energy correlated with solvent coordination strength to PbI 2 at the following sequence: DMSO > DMF > NMP > GBL . Therefore, solvents play important roles in forming MHP, which will drive processing conditions and even the possibility of bypassing the formation of intermediate phases.…”

How the ionic liquid BMIMBF4 influences the formation and optoelectronic properties of MAPbI3 thin films

“…26 Another important aspect affecting the optoelectronic properties of perovskites is their morphology, which in turn is decisively determined by the exact crystallization processes that occur during the solution based thin lm preparation. While developing a general understanding of the perovskite lm formation has been an important research focus for several years, in particular investigated by in situ characterization methods, [27][28][29][30][31][32][33][34][35] the exact role of ionic liquids during solution processing is still not well understood. In particular, it is not yet clear how adding an IL to the precursor solutions leads to the benecial optoelectronic nal lm properties, and whether the IL interacts with the precursors, intermediate states and the perovskite during the lm formation process, possibly inuencing the latter.…”