Origin and structure of polar domains in doped molecular crystals

Meirzadeh, Elena; Azuri, Ido; Qi, Yubo; Ehre, David; Rappe, Andrew M.; Lahav, Meir; Kronik, Leeor; Lubomirsky, Igor

doi:10.1038/ncomms13351

Cited by 38 publications

(63 citation statements)

References 38 publications

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“…The effect of the growth environment, which may induce a permanent dipole due to defects (e.g., as result of the presence of anti-solvent or stabilizer molecules in the lattice) (52), is checked by measuring pyroelectricity from crystals grown in different environments, all below T c (SI Appendix, Fig. S2 A and B).…”

Section: Applied Physical Sciencesmentioning

confidence: 99%

Tetragonal CH ₃ NH ₃ PbI ₃ is ferroelectric

Rakita

Bar-Elli

Meirzadeh

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

262

221

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Halide perovskite (HaP) semiconductors are revolutionizing photovoltaic (PV) solar energy conversion by showing remarkable performance of solar cells made with HaPs, especially tetragonal methylammonium lead triiodide (MAPbI 3 ). In particular, the low voltage loss of these cells implies a remarkably low recombination rate of photogenerated carriers. It was suggested that low recombination can be due to the spatial separation of electrons and holes, a possibility if MAPbI 3 is a semiconducting ferroelectric, which, however, requires clear experimental evidence. As a first step, we show that, in operando, MAPbI 3 (unlike MAPbBr 3 ) is pyroelectric, which implies it can be ferroelectric. The next step, proving it is (not) ferroelectric, is challenging, because of the material's relatively high electrical conductance (a consequence of an optical band gap suitable for PV conversion) and low stability under high applied bias voltage. This excludes normal measurements of a ferroelectric hysteresis loop, to prove ferroelectricity's hallmark switchable polarization. By adopting an approach suitable for electrically leaky materials as MAPbI 3 , we show here ferroelectric hysteresis from well-characterized single crystals at low temperature (still within the tetragonal phase, which is stable at room temperature). By chemical etching, we also can image the structural fingerprint for ferroelectricity, polar domains, periodically stacked along the polar axis of the crystal, which, as predicted by theory, scale with the overall crystal size. We also succeeded in detecting clear second harmonic generation, direct evidence for the material's noncentrosymmetry. We note that the material's ferroelectric nature, can, but need not be important in a PV cell at room temperature.halide perovskites | photovoltaics | semiconductors | ferroelectricity | pyroelectricity N ew optoelectronic materials are of interest for producing solar cells with higher power and voltage efficiencies, lower costs, and improved long-term reliability. A very recent entry is the family of halide perovskites (HaPs), in particular those based on methylammonium (MA) lead iodide (MAPbI 3 ), MAPbBr 3 , and its inorganic analog CsPbBr 3 . Devices based on these perform remarkably well as solar cells (1, 2), as well as in other optoelectronic applications, such as LEDs and electromagnetic radiation detectors (3-5). Understanding possible unique characteristics of HaPs may show the way to other materials with similar key features.The ABX 3 (X = I, Br, Cl) HaP semiconductors (SCs), that is, with perovskite or perovskite-like structures, reach, via a steep absorption edge, a high optical absorption coefficient (∼10 5 cm −1 ) (6, 7), long charge carrier lifetimes (∼0.1-1 μs) (8), and reasonable carrier mobilities (less than or equal to ∼100 cm 2 ·V −1 ·s −1 ) (9), and have a low exciton binding energy (10). With these characteristics, the thickness of the optical absorber layer can be ≤0.5 μm, which allows the charge carriers (separated electrons and holes) to diffuse/d...

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Section: Applied Physical Sciencesmentioning

confidence: 99%

Tetragonal CH ₃ NH ₃ PbI ₃ is ferroelectric

Rakita

Bar-Elli

Meirzadeh

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

262

221

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“…Amino acid compound crystals have been more widely studied for their piezoelectric properties, including L-arginine phosphate (LAP) 32 and triglycine sulfate (TGS) 33 . Doping of centrosymmetric α-glycine crystals with other L-amino acids also leads to crystals with piezoelectric properties 34 . The peptide that has attracted the most attention for its piezoelectric properties is di-phenylalanine (FF), which is easily influenced by external electric fields in aqueous solution 35 .…”

mentioning

confidence: 99%

Organic piezoelectric materials: milestones and potential

2019

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Research on the piezoelectric response of biomolecules has intensified following demonstration of open circuit voltages of over 20 V in biopiezoelectric generators. Organic piezoelectric nanotubes, fibers, and micro-islands have been grown and studied; however, the lack of fundamental understanding of the piezoelectric effect in nature hinders the rational design of biomaterials to provide a tailor-made piezoelectric response. Advances in high performance computing have facilitated the use of quantum mechanical calculations to predict the full piezoelectric tensor of biomolecular crystals, including amino acids and small peptides. By identifying directions of high piezoelectric response, the simulations can guide experimental crystal growth, device fabrication and electrical testing, which have led to the demonstration of unprecedented piezoelectric responses in organic crystals on the order of 200 pC/N. These large responses arise from strong supramolecular dipoles, which can be tuned by molecular chemistry and packing, opening new opportunities for the realization of technologically useful piezoelectric devices from renewable materials. The amino acids predicted to exhibit the highest piezoelectric response, such as glycine, hydroxyproline and lysine, are anticipated to be used to engineer highly piezoelectric peptides in the future. With improved scaling of advanced computational methods, such as density functional perturbation theory, the research community can begin to efficiently screen peptide structures for enhanced electromechanical properties. This capability will accelerate the experimental development of devices and provide much-needed insight into the evolution of a hierarchical relation in biological materials starting from strongly piezoelectric building blocks.

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“…[ 11 ], the current

decays with time as:

where

[ 17 ] is the thermal diffusion coefficient of

-gly and

is the current at

= 0. Fitting the

vs.

dependence to

-function leads to the value of

= 288 ± 25 µm ( Figure 1 b), which matches the previous estimates [ 17 ]. The fact that the current-time response can be fitted with high degree of confidence to Equaion (3) at all temperatures implies ( Figure 1 a) that the polarization is constant within the surface layer.…”

Section: Resultsmentioning

confidence: 99%

Surface Piezoelectricity and Pyroelectricity in Centrosymmetric Materials: A Case of α-Glycine

et al. 2020

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Surface pyroelectricity and piezoelectricity induced by water incorporation during growth in α-glycine were investigated. Using the periodic temperature change technique, we have determined the thickness (~280 µm) of the near surface layer (NSL) and its pyroelectric coefficient (160 pC/(K × cm2) at 23 °C) independently. The thickness of NSL remains nearly constant till 60 °C and the pyroelectric effect vanishes abruptly by 70 °C. The piezoelectric effect, 0.1 pm/V at 23 °C measured with an interferometer, followed the same temperature dependence as the pyroelectric effect. Abrupt disappearance of both effects at 70 °C is irreversible and suggests that water incorporation to α-glycine forms a well defined near surface phase, which is different form α-glycine because it is polar but it too close to α-glycine to be distinguished by X-ray diffraction (XRD). The secondary pyroelectric effect was found to be <14% of the total, which is unexpectedly small for a material with a large thermal expansion coefficient. This implies that water incorporation infers minimal distortions in the host lattice. This finding suggests a path for the control of the piezoelectric and pyroelectric effects of the crystals using stereospecific incorporation of the guest molecules.

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Origin and structure of polar domains in doped molecular crystals

Cited by 38 publications

References 38 publications

Tetragonal CH ₃ NH ₃ PbI ₃ is ferroelectric

Tetragonal CH ₃ NH ₃ PbI ₃ is ferroelectric

Organic piezoelectric materials: milestones and potential

Surface Piezoelectricity and Pyroelectricity in Centrosymmetric Materials: A Case of α-Glycine

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Origin and structure of polar domains in doped molecular crystals

Cited by 38 publications

References 38 publications

Tetragonal CH 3 NH 3 PbI 3 is ferroelectric

Tetragonal CH 3 NH 3 PbI 3 is ferroelectric

Organic piezoelectric materials: milestones and potential

Surface Piezoelectricity and Pyroelectricity in Centrosymmetric Materials: A Case of α-Glycine

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Product

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Tetragonal CH ₃ NH ₃ PbI ₃ is ferroelectric

Tetragonal CH ₃ NH ₃ PbI ₃ is ferroelectric