Abstract
The current understanding of the crystallization, morphology evolution, and phase stability of wide-bandgap hybrid perovskite thin films is very limited, as much of the community's focus is on lower bandgap systems. Herein, the crystallization behavior and film formation of a wide and tunable bandgap MAPbBr(3-x)Cl(x) system are investigated, and its formation and phase stability are contrasted to the classical MAPbI(3-x)Br(x) case. A multiprobe in situ characterization approach consisting of synchrotron-based grazing incidence wide-angle X-ray scattering and laboratory-based time-resolved UV-Vis absorbance measurements is utilized to show that all wide-bandgap perovskite compositions of MAPbBr(3-x)Cl(x) studied (0 < x < 3) crystallize the same way: the perovskite phase forms directly from the colloidal sol state and forms a solid film in the cubic structure. This results in significantly improved alloying and phase stability of these compounds compared with MAPbI(3-x)Br(x) systems. The phase transformation pathway is direct and excludes solvated phases, in contrast to methylammonium lead iodide (MAPbI(3)). The films benefit from antisolvent dripping to overcome the formation of discontinuous layers and enable device integration. Pin-hole-free MAPbBr(3-x)Cl(x) hybrid perovskite thin films with a tunable bandgap are, thus, integrated into working single-junction solar cell devices and achieve a tunable open-circuit voltage as high as 1.6 V.