Wide and Tunable Bandgap MAPbBr_3−xCl_x Hybrid Perovskites with Enhanced Phase Stability: In Situ Investigation and Photovoltaic Devices

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−xCl_x system are investigated, and its formation and phase stability are contrasted to the classical MAPbI_3−xBr_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−xCl_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−xBr_x systems. The phase transformation pathway is direct and excludes solvated phases, in contrast to methylammonium lead iodide (MAPbI₃). The films benefit from antisolvent dripping to overcome the formation of discontinuous layers and enable device integration. Pin-hole-free MAPbBr_3−xCl_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.