Synergistic Effect of PbI₂ Passivation and Chlorine Inclusion Yielding High Open-Circuit Voltage Exceeding 1.15 V in Both Mesoscopic and Inverted Planar CH3NH₃PbI₃(Cl)-Based Perovskite Solar Cells

Enhancing open-circuit voltage in CH₃NH₃PbI₃(Cl) perovskite solar cells has become a major challenge for approaching the theoretical limit of the power conversion efficiency. Here, for the first time, it is demonstrated that the synergistic effect of PbI₂ passivation and chlorine incorporation via controlling the molar ratio of PbI₂, PbCl₂ (or MACl), and MAI in the precursor solutions, boosts the open-circuit voltage of CH₃NH₃PbI₃(Cl) perovskite solar cells over 1.15 V in both mesoscopic and inverted planar perovskite solar cells. Such high open-circuit voltage can be attributed to the enhanced photoluminescence emission and carrier lifetime associated with the reduced trap densities. The morphology and composition analysis using scanning electron microscopy, X-ray diffraction measurements, and energy dispersive X-ray spectroscopy confirm the high quality of the optimized CH₃NH₃PbI₃(Cl) perovskite film. On this basis, record-high efficiencies of 16.6% for nonmetal-electrode all-solution-processed perovskite solar cells and 18.4% for inverted planar perovskite solar cells are achieved.