used with dimethylformamide (DMF), dimethylsulfoxide (DMSO), or gamma butyrolactone. [1b,3,4] The precursor film is then converted to the perovskite structure by annealing on a hot plate at 60-200 °C. The high temperature treatment however spoils the film properties by generating intrinsic defects, stoichiometric or compositional changes, rapid film degradation, uncontrollable perovskite precipitation, inhomogeneous perovskite crystallization at the perovskite/underlayer interface, and incomplete surface coverage with a random film texture. [5] To avoid high temperature annealing processes, solution-based methods have been developed. However, in those studies, the perovskite colloidal particles are synthesized in solution and then deposited on the underlayer film without elimination of annealing. [6][7][8] They are enabled by the addition of small molecules, use of an excess organic component, or treatment with hypophosphorous acid. Therefore, these solution reactions still require high temperature and thus cannot avoid unmanageable surface reactions resulting in nonstoichiometric dopants and phase segregation. [9] In order to lower the reaction temperature, acid-treated methods including acidcatalyzed techniques [10] and acid-base solutions [11] have been developed particularly for mixed [12,13] and single halides [14] in DMF. [15][16][17][18][19] The acid-catalyzed reactions are, in general, initiated by the formation of solvated PbI 4 2− anions that further react with CH 3 NH 3 + cations for CH 3 NH 3 PbI 3 (s) (MAPbI 3 )
Methylammonium lead iodide (MAPbI 3 ) perovskites are organic-inorganic semiconductors with long carrier diffusion lengths serving as the light-harvesting component in optoelectronics.Through a substitutional growth of MAPbI 3 catalyzed by polar protic alcohols, evidence is shown for their substrate-and annealing-free production and use of toxic solvents and high temperature is prevented. The resulting variable-sized crystals (≈100 nm-10 µm) are found to be tetragonally single-phased in alcohols and precipitated as powders that are metallic-lead-free. A comparatively low MAPbI 3 yield in toluene supports the role of alcohol polarity and the type of solvent (protic vs aprotic). The theoretical calculations suggest that overall Gibbs free energy in alcohols is lowered due to their catalytic impact. Based on this alcohol-catalyzed approach, MAPbI 3 is obtained, which is chemically stable in air up to ≈1.5 months and thermally stable (≤300 °C). This method is amendable to large-scale manufacturing and ultimately can lead to energy-efficient, low-cost, and stable devices.