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

Jade Casasent Author

07/28/2021 Added

43 Plays

Description

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

Searchable Transcript

Search:

[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.

The screen size you are trying to search captions on is too small!

You can always jump over to MediaHub and check it out there.

Comments

0 Comments

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

Description

Searchable Transcript

Comments icon comment

Related Channels

Comments