Superior Performance of Two-Phase Triple Halide Inorganic Perovskites

Inorganic halide perovskites are attractive for achieving the wide bandgap optimal for a high-efficiency perovskite-perovskite tandem photovoltaic based on today’ Pb-Sn low bandgap compositions. However, they have suffered from lower photoluminescent quantum yield relative to hybrid compositions and phase instability. To improve upon metastable CsPbI3, we explore triple-halide alloying of minor amounts of Br and Cl with I. In agreement with previous reports for hybrid analogues, we observe a chlorine solubility limit in the majority iodine-bromine all-inorganic perovskite lattice. Past this solubility limit we observe the perovskite forming a split phase of iodine-bromine-rich and bromine-chlorine-rich clusters. Interestingly, these dual-phase thin films show superior and long lasting PL-intensity under 40-sun equivalent 633 nm laser intensity, which hints at possible synergistic effects of this chemical heterogeneity. We leverage multi-modal synchrotron microscopy and correlative spectroscopic micro-photoluminescence (µPL) on all-inorganic triple halide perovskites CsPbX3 (X-site: I/Br/Cl) films to elucidate mechanisms for superior performance in the face of phase segregation. The results suggest that a greater focus on harnessing the flexibility of the inorganic perovskite material system holds promise to retrace the outstanding performance and stability gains made in hybrid analogues.