Secondary Phase Particles in Cesium Lead Bromide Perovskite Crystals: An Insight into the Formation of Matrix-Controlled Inclusion.

The metal halide perovskite CsPbBr3 bulk crystals present electrical and optical performance discrepancy since the grown-in defects. Here, we first report the well-defined secondary phase (SP) particles of CsPb2Br5 with polyhedral morphology in CsPbBr3 crystals grown by the vertical Bridgman method. The resulting polyhedral morphology of CsPb2Br5 particles associated with the trapping of PbBr2-rich droplets have been discussed on the basis of the "matrix-controlled" growth. Two morphological evolution paths are proposed, which result in a regular cube SP particle comprised by {100} facets for the final equilibrium. Furthermore, the wafer with superior optical transmittance exhibits a higher photoelectric response on-off ratio (∼2000) in contrast to ∼80 for the wafer with high density SP particles. The corresponding hole mobility (μh) is calculated with the values 289.99 and 26.91 cm-2·V-1·s-1, respectively. The variation of μh is attributed to the carrier transport trajectory affected by SP induced trapping defects and the weak combination.