Direct Visualization of General Ferroelasticity Across Hybrid and Inorganic Lead Halide Perovskites

Jade Casasent Author

07/28/2021 Added

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We are looking at ferroelasticity using non-polarized light across MAPbBr3 and CsPbBr3

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[00:00:00.810]Hello everyone. My name is Jade Casasent
[00:00:03.440]and today, I'm going to be talking about
[00:00:04.940]the direct visualization of general ferroelasticity
[00:00:08.180]across hybrid organic inorganic
[00:00:10.540]and all inorganic lead halide perovskite crystals.
[00:00:13.820]So to begin, lead halide perovskites
[00:00:15.980]are solution-processable semiconductor with a 3D structure
[00:00:19.930]in the form ABX3, where A is methyl ammonium or Cesium,
[00:00:23.810]B is Lead and X is a Halide,
[00:00:26.150]which in this case, we're using bromide.
[00:00:28.290]These are being used for different
[00:00:29.690]optoelectronic applications, such as solar cells,
[00:00:32.630]LEDs, lasers, and photo detectors.
[00:00:35.310]But the problem is that there's a lot that is not understood
[00:00:37.940]and unknown about these crystals.
[00:00:39.850]Specifically, we are looking at and trying to understand
[00:00:42.890]more about ferroelasticity
[00:00:44.740]and how that affects the chemical activity
[00:00:46.780]in the electronic properties of these crystals.
[00:00:49.480]So the hallmark of ferroelastic materials
[00:00:51.880]is that it has a coherent and switchable twin domains.
[00:00:55.480]So in figure four,
[00:00:56.313]you see these stripes are domain walls
[00:00:59.350]using a polarized light microscope.
[00:01:01.910]So ferroelasticity is similar to ferromagnetism,
[00:01:04.910]which is where a material can change its magnetic dipole in
[00:01:07.690]the presence of a permanent magnet.
[00:01:09.790]But for ferroelasticity, we have a coherent change
[00:01:12.900]that does not break the material in the presence of stress.
[00:01:16.200]And so these domain walls
[00:01:17.360]are commonly seen using polarized light,
[00:01:20.150]which is shown in figure four,
[00:01:22.170]but this is because of bio fringes typically.
[00:01:25.520]And so we are trying to see if we can
[00:01:27.610]see it without using polarized light,
[00:01:29.970]if they're evident across phase changes
[00:01:32.050]and if they're evident in organic and organic hybrid
[00:01:34.870]and all inorganic crystals.
[00:01:37.240]So the first thing we had to do was grow these crystals.
[00:01:40.110]And this was based on solubility,
[00:01:41.820]where we tried to decrease the solubility of the solution to
[00:01:44.930]have the crystals precipitate out.
[00:01:46.940]And the first method we used was ITC
[00:01:49.060]or inverse temperature crystallization,
[00:01:51.400]where we slowly heated the precursor solution
[00:01:53.730]to decrease it solubility
[00:01:55.073]and have a methyl ammonium led bromide crystal
[00:01:57.980]precipitate out.
[00:01:59.370]The second method, AVC or anti solvent vapor
[00:02:02.500]is a safe crystallization
[00:02:04.200]is where we place our precursor solution,
[00:02:06.260]which had a good solvent into one container that contained
[00:02:10.630]an anti-solvent and decrease the solubility of our
[00:02:13.660]solution and we slowly had
[00:02:15.387]methyl ammonium lead bromide crystal
[00:02:17.700]precipitate out of solution.
[00:02:19.830]The third method, STL,
[00:02:21.780]which is solution, temperature lowering is where we slowly
[00:02:24.890]cool down the precursor solution to diffuse the solubility
[00:02:29.290]and we had a cesium Lead bromide crystal precipitate out.
[00:02:33.090]After we grew the crystal,
[00:02:34.430]we used powder x-ray diffraction
[00:02:36.500]to verify the crystals composition,
[00:02:39.160]and then after that,
[00:02:40.130]we placed the crystals
[00:02:41.360]inside this device shown on the bottom left.
[00:02:44.220]And this is where we cool the heated crystals.
[00:02:46.840]And we observed the temperature changes and
[00:02:49.957]the changes that happen when we applied stress
[00:02:52.630]by using a non-polarized light microscope.
[00:02:55.670]After that, we measured the optical properties
[00:02:58.170]using photoluminescence and absorbance spectroscopy.
[00:03:00.830]So in the bottom right you can see your spectroscopy set up
[00:03:04.140]and you can see the green light,
[00:03:06.000]which is the laser that we use for PL
[00:03:08.570]and then for absorbance,
[00:03:10.010]we measure reflectance and converted it into absorbance,
[00:03:12.773]and we use a lamp instead of a laser.
[00:03:17.050]And now we're looking at the XRD data
[00:03:19.030]for methyl-ammonium on the left.
[00:03:21.290]And so in the top on blue,
[00:03:23.000]we have our experimental data
[00:03:24.540]and on the bottom and black
[00:03:26.610]we have the simulated data.
[00:03:28.440]And because they're very similar,
[00:03:29.880]we can say that our material is in fact,
[00:03:32.650]methyl-ammonium lead bromide
[00:03:34.300]and on the right, we have a cubic structure
[00:03:36.850]for methyl-ammonium lead bromide.
[00:03:38.430]And this is a phase that it's in at room temperature.
[00:03:42.420]We have the same thing, but now for cesium.
[00:03:45.100]And so we can see
[00:03:47.180]on the top in blue is our experimental data,
[00:03:49.780]and on the bottom and black,
[00:03:51.160]is there a simulated data.
[00:03:52.780]And again, they match very well until we can say
[00:03:55.590]that we do in fact, have cesium lead bromide.
[00:03:59.080]And then on the right,
[00:03:59.913]we have an orthorhombic structure for cesium lead bromide
[00:04:02.410]and that's the phase that it's in at room temperature.
[00:04:07.050]And now that we verify that we do in fact,
[00:04:09.270]have the materials we thought
[00:04:10.720]we now measure the optical properties
[00:04:12.761]using photoluminescence and absorbance spectroscopy.
[00:04:16.110]So on the left, we have methyl-ammonium
[00:04:17.720]and on the right, we have Caesium lead bromide.
[00:04:20.930]And so from this data,
[00:04:21.830]we're able to look at the optical band gap
[00:04:23.930]and determined that our materials are semiconductors,
[00:04:26.820]which is what's expected from them.
[00:04:30.240]Now that we have looked at these optical properties and
[00:04:32.710]verified that we do have the crystals we thought,
[00:04:35.310]we're now looking at the phase changes and
[00:04:37.480]switching of domain malls of methyl-ammonium lead room.
[00:04:41.090]So we begin by looking at it
[00:04:43.020]at room temperature in a cubic phase
[00:04:45.170]and we know that it's the cubic phase
[00:04:47.610]because the cubic is a high symmetry phase,
[00:04:49.760]so we see no domain walls or stripes on the crystal,
[00:04:53.223]then we slowly cooled down the crystal
[00:04:55.330]and we enter the tetragonal phase,
[00:04:57.140]and we see these domain walls or strip starts to appear.
[00:05:00.205]We slowly cool even further,
[00:05:02.618]and we see these domain walls or stripes switch as we enter
[00:05:06.480]the incommensurate phase and we cool even further
[00:05:09.870]to enter the orthorhombic phase.
[00:05:11.420]And we see these domain walls,
[00:05:13.300]stripes switch again and more up here.
[00:05:16.910]And this is very much the coherence switching
[00:05:20.230]as an indication of ferroelasticity
[00:05:22.850]for methyl-ammonium lead bromide.
[00:05:25.370]And so in this video,
[00:05:27.010]we can see the consecutive domain
[00:05:28.730]wall switching very clearly
[00:05:30.710]and although people have seen these domain walls before,
[00:05:33.530]it's all been done using polarized light,
[00:05:36.130]and so the fact that we can see it using
[00:05:38.120]non-polarized light is very surprising.
[00:05:43.460]Next, we do the same thing, but for cesium lead bromide.
[00:05:46.880]And so we started at the orthorhombic phase
[00:05:49.200]at room temperature for cesium.
[00:05:51.330]And because the orthorhombic phase is a low symmetry phase,
[00:05:55.140]we do see these domain walls
[00:05:57.100]are stripes at room temperature.
[00:05:59.490]And so we slowly heated the crystal up
[00:06:01.724]and we entered the tetragonal phase
[00:06:03.910]and we see these domain walls
[00:06:05.360]or stripes switch and more appear.
[00:06:07.740]And then we continue to heat the crystal up,
[00:06:10.450]And we, right before we got to the cubic phase,
[00:06:13.106]we see lots of stripes or domain walls appear
[00:06:16.360]all over the crystal.
[00:06:18.720]And then as we heated into the cubic phase,
[00:06:21.080]all the stripes went away,
[00:06:22.403]which is what we would expect
[00:06:24.220]because this is a high symmetry phase,
[00:06:26.147]and so that's how we know that
[00:06:27.590]we have entered the cubic phase.
[00:06:30.190]And so in this consecutive domain wall switching
[00:06:32.550]is very much an indication that
[00:06:33.979]Cesium lead bromide is in fact ferroelastic,
[00:06:38.210]which is surprising because this has
[00:06:39.640]not been seen before for cesium.
[00:06:42.450]And so we have another video just showing these changes
[00:06:45.800]and because both methyl-ammonia
[00:06:47.430]and cesium lead bromide are ferroelastic,
[00:06:50.460]We can say that there's a general ferroelasticity across
[00:06:53.320]organic inorganic boundary
[00:06:55.330]for lead halide perovskites crystals.
[00:07:00.170]And so finally, to further verify ferroelasticity,
[00:07:03.630]we place a cesium lead bromide crystal
[00:07:05.830]between two microscope slides
[00:07:07.419]and gently press down and applied stress,
[00:07:10.330]and we can see the domain wall
[00:07:11.990]that was here before the stress was applied,
[00:07:14.200]quickly changes directions as the stress is applied,
[00:07:17.990]further indicating ferroelasticity for cesium.
[00:07:21.740]So in conclusion,
[00:07:22.950]we use XRD data to verify the composition of our crystals.
[00:07:26.446]Next, we looked at the band edge, electronic transitions,
[00:07:29.860]using photoluminescence, PL and absobance spectroscopy.
[00:07:34.330]And finally, we directly visualize the ferroelaastic
[00:07:37.400]twin domain topography using non-polarized light microscopy.
[00:07:41.740]We also found that there was a consecutive reversible
[00:07:44.240]phase change seen by domain wall switching
[00:07:46.910]and that there was a general ferroelasticity
[00:07:49.000]across lead halide perovskites.
[00:07:52.190]Thank you for listening to my presentation.

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Direct Visualization of General Ferroelasticity Across Hybrid and Inorganic Lead Halide Perovskites

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