Wide and Tunable Bandgap MAPbBr3-xClx Hybrid Perovskites with Enhanced Phase Stability: In Situ Investigation and Photovoltaic Devices

Our 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 has been on lower bandgap systems. Here, we investigate the crystallization behavior and film formation of wide and tunable bandgap MAPbBr3-xClx films and contrast its formation and phase stability to the classical MAPbI3-xBrx cases. We utilize a multi-probe in situ characterization approach consisting of synchrotron-based grazing incidence wide-angle X-ray scattering and lab-based time-resolved UV-Vis absorbance measurements to show that all wide-bandgap perovskite compositions of MAPbBr3-xClx studied (0 < × < 3) crystallized 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 phase stability of these compounds compared to MAPbI3-xBrx systems. The phase transformation pathway is direct and excludes solvated phases, in contrast to MAPbI3. The films benefit from antisolvent dripping to overcome the formation of discontinuous layers and enable device integration. Pin-hole-free MAPbBr3-xClx hybrid perovskite thin films with tunable bandgap are thus integrated into working single-junction solar cell devices and achieve tunable open-circuit voltage as high as 1.6 V.