Low Defect Density and Anisotropic Charge Transport Enhanced Photo Response in Pseudo-cubic Morphology of MAPbI₃ Single Crystals

The optoelectronic performances of MAPbI3 are related to film morphology and crystal orientation. However, it is difficult to directly quantify the optoelectronic anisotropy in thin films because controlling growth-oriented grains and measuring the optoelectronic difference within micro–nono regions have great technological challenges. Here, taking advantages of the pseudo-cubic morphology of MAPbI3 single crystals (SCs) exposed with (110), (002), and (200) facets, the optoelectronic anisotropies are compared. It reveals that the periodic positive and negative potential distributions at the outermost (110) surface, the orientations of MA+ dipoles, and the stacking of PbI6 octahedrons ensure (110) planes have lower defect densities (VI+, VMA–, I–, MA+, or Ii–, etc.), which therefore enhance photo recycling, deduce the dark current, and increase the photocurrent. Besides, the periodic MA+ and I– arrangements at the (110) surface also restrict ion migrations compared to those of (200) planes. In addition, by comparing the optoelectronic properties of (200) planes of the pseudo-cubic and rhombic dodecahedral MAPbI3 SCs, it is found that the room-temperature-grown pseudo-cubic MAPbI3 SC possesses lower intrinsic defect densities and thus enhances the photo response.