Abstract
Charged ferroelectric domain walls are fascinating electrical topological defects that can exhibit unusual properties. Here, in the search for novel phenomena, we perform and analyze first-principles calculations to investigate the effect of domain width on properties of domains with charged walls in the photovoltaic material consisting of methylammonium lead iodide hybrid perovskite. We report that such domains are stable and have rather low domain wall energy for any investigated width (that is, up to 13 lattice constants). Increasing the domain width first linearly decreases the electronic band gap from ≃1.4 eV to about zero (which therefore provides an efficient band-gap engineering), before the system undergoes an insulator-to-metal transition and then remains metallic (with both the tail-to-tail and head-to-head domain walls being conductive) for the largest widths. All these results can be understood in terms of: (i) components of polarization along the normal of the domain walls being small in magnitude; (ii) an internal electric field that is basically independent of the domain width; and (iii) rather negligible charge transfer between walls. These findings deepen the knowledge of charged ferroelectric domain walls and can further broaden their potential for applications, particularly in the context of halide perovskites for photovoltaics.
Highlights
Organometal halide (OMH) perovskites, such as methylammonium lead iodide (MAPbI3), have experienced an improvement of power conversion photovoltaic efficiency from 3.8% to a recent 22% in a rather short period of time.1,2 their ease and low cost of processing and wide range of applications, further explain why OMH perovskites are among the most currently investigated materials.One important feature of OMH perovskites is the existence of domains and their possible effects on properties
Crystallographic twin domains with sizes of 100–300 nm have been measured by transmission electron microscopy (TEM) in MAPbI3,14 and highly ordered domains15,16 with alternating polarization and a width of 90 nm were detected by piezoresponse force microscopy (PFM)
As consistent with the literature,34 we numerically find that two particular structures present the lowest energies among different polar phases of MAPbI3 monodomains: (1) one triclinic structure with P1 space group, which has a polarization equal to (4.2, 0, 12.7)μC/cm2 and a θ vector of (69.6°, 90°, 20.4°); and (2) a rhombohedral structure with R3m space group, with a polarization of (7.1, 7.1, 7.1)μC/cm2 and a θ vector equal to (54.7°, 54.7°, 54.7°)
Summary
Organometal halide (OMH) perovskites, such as methylammonium lead iodide (MAPbI3), have experienced an improvement of power conversion photovoltaic efficiency from 3.8% to a recent 22% in a rather short period of time. their ease and low cost of processing and wide range of applications (e.g., solar cells, photodetectors, and lasing8–12), further explain why OMH perovskites are among the most currently investigated materials.One important feature of OMH perovskites is the existence of domains and their possible effects on properties. Organometal halide (OMH) perovskites, such as methylammonium lead iodide (MAPbI3), have experienced an improvement of power conversion photovoltaic efficiency from 3.8% to a recent 22% in a rather short period of time.. Organometal halide (OMH) perovskites, such as methylammonium lead iodide (MAPbI3), have experienced an improvement of power conversion photovoltaic efficiency from 3.8% to a recent 22% in a rather short period of time.1,2 Their ease and low cost of processing and wide range of applications (e.g., solar cells, photodetectors, and lasing8–12), further explain why OMH perovskites are among the most currently investigated materials. Based on first-principles calculations, Frost et al. propose that the existence of charged ferroelectric domain walls should lead to the separation of photoexcited electron and hole pairs. First-principles simulations demonstrated that charged ferroelectric domain walls in OMH perovskites have rather different optical spectra than neutral ones in addition to having much smaller bandgaps, as a result of the associated built-in electric fields
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