Material exploration via designing spatial arrangement of octahedral units: a case study of lead halide perovskites

Pengfei Fu,Jiang Tang,Zewen Xiao,Sanlue Hu

doi:10.1007/s12200-021-1227-z

Abstract

Halide perovskites have attracted tremendous attention as semiconducting materials for various optoelectronic applications. The functional metal-halide octahedral units and their spatial arrangements play a key role in the optoelectronic properties of these materials. At present, most of the efforts for material exploration focus on substituting the constituent elements of functional octahedral units, whereas designing the spatial arrangement of the functional units has received relatively little consideration. In this work, via a global structure search based on density functional theory (DFT), we discovered a metastable three-dimensional honeycomb-like perovskite structure with the functional octahedral units arranged through mixed edge- and corner-sharing. We experimentally confirmed that the honeycomb-like perovskite structure can be stabilized by divalent molecular cations with suitable size and shape, such as 2,2′-bisimidazole (BIM). DFT calculations and experimental characterizations revealed that the honeycomb-like perovskite with the formula of BIMPb2I6, synthesized through a solution process, exhibits high electronic dimensionality, a direct allowed bandgap of 2.1 eV, small effective masses for both electrons and holes, and high optical absorption coefficients, which indicates a significant potential for optoelectronic applications. The employed combination of DFT and experimental study provides an exemplary approach to explore prospective optoelectronic semiconductors via spatially arranging functional units.

Highlights

The high symmetry and connectivity of the [BX6] octahedra in these perovskites account for high electronic dimensionality [22], which is the primary enabler for the superior optoelectronic properties
Via a global structure search using CsPbI3 as a paradigm, we discovered a metastable 3D honeycomb-like perovskite structure with the [PbI6] functional octahedral units arranged by a mixed edge- and corner-sharing means
Like the α-CsPbI3 and γCsPbI3 perovskites, the honeycomb-like CsPbI3 is a metastable structure with even higher formation energy (i.e., 9.0 meV/atom, higher than that of α-CsPbI3) and should be converted to the δ-CsPbI3 nonperovskite even if the honeycomb-like CsPbI3 was successfully synthesized under certain conditions

Summary

Introduction

With the common formula ABX3 — where A is an organic or alkali cation, B is commonly Pb2+, and X is a halogen anion — have attracted tremendous attention as semiconducting materials for thin-film solar cells [1,2] and for photodetectors [3,4,5] and light-emitting diodes (LEDs) [6,7,8,9] due to their superior optoelectronic properties [10,11,12] — such as suitable direct allowed bandgaps [13], small effective masses for both holes and electrons [14], high optical absorption coefficients [15], long photogenerated carrier diffusion lengths and lifetimes [16], and high defect tolerance [17,18,19,20] — as well as solution processability that enables low production costs These perovskites consist of a three-dimensional (3D) corner-sharing network of [BX6] octahedra (i.e., BX3), with the “A” cations occupying 12-fold cuboctahedral voids within the network and counterbalancing the charge of [BX3]– extended anion.

Results and discussion

Conclusions

Experimental section