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

Abstract

The optoelectronic performances of MAPbI 3 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 MAPbI 3 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 PbI 6 octahedrons ensure (110) planes have lower defect densities (V I + , V MA − , I − , MA + , or I i − , 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 MAPbI 3 SCs, it is found that the roomtemperature-grown pseudo-cubic MAPbI 3 SC possesses lower intrinsic defect densities and thus enhances the photo response.

Monocrystalline Methylammonium Lead Halide Perovskite Materials for Photovoltaics

“…Figure summarizes optoelectronic properties probed on different crystal facets for MAPX SC fabricated and characterized in similar conditions, unambiguously demonstrating the existence of anisotropy in the optoelectronic properties of MAPX. [ 63,64,187,188 ]…”

“…[ 192 ] Mobile ions are also responsible for the formation of an anisotropic built‐in field that can affect electronic and ionic transport through the crystal. [ 64,188 ] Crystallographic planes such as (110) and (002) (MAPI) presenting a mix of positive and negative ions are thought to hinder ionic migration and limit the formation of a built‐in field, and could enable better/faster photo‐response of devices, unlike the (200) plane which is I − rich. [ 188 ]…”

“…[ 64,188 ] Crystallographic planes such as (110) and (002) (MAPI) presenting a mix of positive and negative ions are thought to hinder ionic migration and limit the formation of a built‐in field, and could enable better/faster photo‐response of devices, unlike the (200) plane which is I − rich. [ 188 ]…”

“…Figure 22 summarizes optoelectronic properties probed on different crystal facets for MAPX SC fabricated and characterized in similar conditions, unambiguously demonstrating the existence of anisotropy in the optoelectronic properties of MAPX. [63,64,187,188] MAPI: In bulk MAPI-SC grown by ITC, the (100) facet displayed a trap density (2.8 × 10 13 cm −3 ) 4× lower than the (112) facet and higher photoluminescence (Figure 22a), [187] and for MAPI SC grown by AVC, the (110) facet was shown to have a trap density (5.4 × 10 9 cm −3 ) 2× lower than (002) and ( 200) facets (Figure 22b). [188] While bulk SC can hardly be integrated at such in solar cells, it is possible to build planar photodetectors by depositing gold electrodes on one of the naturally 110), ( 100), (101), and (001) planes, indicated by the red dashed lines.…”

“…b) Trap density of MAPI ( 110), (002), (200) facets (data from ref. [188]). c) Trap density and mobility of MAPB (100) (110) (111) facets (data from refs.…”