Enhancing Ferroelectric Dipole Ordering in Organic–Inorganic Hybrid Perovskite CH₃NH₃PbI₃: Strain and Doping Engineering

Abstract

Organic–inorganic hybrid perovskites with a prototype formula MAPbI3 (MA = CH3NH3) have shown great promise in next-generation solar cells, yet a full understanding of their high power conversion efficiency relative to their inorganic counterparts has not been achieved. One of the most plausible arguments for their high efficiency is the ability of organic cations to form ferroelectric (FE) domains. By using first-principles calculations to examine the rotational behavior of MA cations in MAPbI3, here we show a relationship between the lattice structures and the FE dipole ordering of MA cations. It is found that the MA cations could form a spontaneous FE dipole ordering in tetragonal MAPbI3 at room temperature. The tendency of the FE formation is strongly related to the ratio of lattice parameters of MAPbI3. On the basis of the developed structure–ferroelectric-property relationship, we propose that a biaxial or uniaxial compressive strain and an anion doping with small halogen ions can further enhance the FE dipole ordering. These findings are in good agreement with the experimental discoveries that high-performance solar cells always incorporate mixed halide hybrid perovskites involving Br or Cl ions. This work may provide some guidelines for rational designs of highly efficient hybrid perovskite solar cells.

Probing of Local Multifield Coupling Phenomena of Advanced Materials by Scanning Probe Microscopy Techniques

“…However, the experimental observations are quite controversial mainly due to the large leakage and degradation of IOHP under electric field during the ferroelectric measurements. Good news is that ferroelasticity of IOHP has been proved by solid evidences, which makes strain engineering a potential method to further tune the properties of IOHP . Using PFM, some recent works also reported the effects from ordered ferroelectric domains, and optically induced polarization switching of IOHP .…”

On the Current–Voltage Hysteresis in Perovskite Solar Cells: Dependence on Perovskite Composition and Methods to Remove Hysteresis

“…Photoferroelectric property was observed from 2D bis(cyclohexylaminium) tetrabromo lead perovskite, where polarization characteristics was proposed to be related to superior photovoltaic property of PSC . Along with theoretical approaches, experimental evidences on ferroelectricity were also reported, where tetragonal phase of single crystal MAPbI 3 was ferroelectric and self‐organized, room‐temperature stable ferroelectric domain might affect charge carrier extraction . Regarding origin of ferroelectricity, off‐center displacement of lead in lead‐iodide octahedral was suggested to be origin of ferroelectricity, while dipole ordering of organic cation is related to ferroelectricity .…”

Strain–Chemical Gradient and Polarization in Metal Halide Perovskites

“…Even in nonferroelectric materials, moving ions could tie to lattice strain to result in electric polarization in MHPs via Vegard effect and/or flexoelectric effect,13 which can produce signals analogous to ferroelectricity in piezoresponse force microscopy (PFM, a commonly utilized technique in ferroelectric/piezoelectric studies) 14. In ferroelectric materials, moving ions can interact with ferroic behaviors through compensating the electric field and the elastic field, creating a mixed ferroic–ionic response that could either reduce the field due to the screening of ferroelectric polarization or increase the field due to elastic compensation effects 11,15. These interactions resulting from moving ions lead to the difficulty in revealing the origin of polarization in MHPs, therefore, exploring how moving ions affect the polarization of MHPs becomes particularly important to the development of MHP optoelectronics.…”