Simulating Angular Distribution of Light in the Back Focal Plane: Emission Properties of Lead Halide Perovskites

Trey Maddaleno Author

07/28/2020 Added

40 Plays

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A model was created in order to simulate the angular distribution of emitted light from perovskite crystals, which will serve as a powerful in determining the dipole orientations of observed crystals.

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[00:00:00.452]Hello everyone!
[00:00:01.592]I'm Trey Maddaleno, and today I will be
[00:00:03.727]presenting some of the research that
[00:00:05.554]I did this summer, which was about
[00:00:07.299]simulating the angular distribution
[00:00:09.294]of light in the back focal plane
[00:00:10.904]in order to study lead halide pervoskites.
[00:00:14.189]Optoelectronic devices - that is -
[00:00:16.019]technology like photovoltaic cells, lasers,
[00:00:18.856]LEDS, and detector materials
[00:00:21.573]are all in need of improvement in order to
[00:00:23.828]become more efficient and less expensive.
[00:00:26.204]A promising and relatively new material
[00:00:28.534]with applications in optoelectronic devices
[00:00:31.224], especially detectors,
[00:00:32.423]are lead halide perovskites,
[00:00:33.960], but they need to be further studied
[00:00:36.193]before they are implemented
[00:00:37.963]on a wider scale
[00:00:39.023]You may think,
[00:00:40.172]"What does a perovskite look like?"
[00:00:41.902]Well, on a macro scale, they look like
[00:00:43.302]the single crystal shown here in this photo
[00:00:44.835]which allows for easy study with spectroscopy.
[00:00:47.169]On a much smaller scale,
[00:00:48.805]you can look at the crystal structure
[00:00:50.965]which entails a central atom such as lead
[00:00:53.599]face atoms such as halides - bromide, iodide -
[00:00:57.322]and corner atoms such as
[00:00:59.822]the methylammonium cation.
[00:01:01.542]Here you can see a representation of a typical 4f system,
[00:01:04.493]which is common for imaging.
[00:01:06.413]Most research concerning perovskites is based on traditional spectroscopy:
[00:01:09.867]focusing light onto the image plane and observing frequency, intensity, and other values.
[00:01:15.017]Information about the angular distribution of emitted light is lost though.
[00:01:19.017]This quantity can be observed using what is called energy-momentum spectroscopy.
[00:01:23.017]In the simplest terms, that is observing light in the Fourier plane, or back focal plane,
[00:01:28.297]which yields information about the directionality of the emitted light and emission dipoles.
[00:01:33.508]Before this type of spectroscopy can be performed in the lab though,
[00:01:37.508]it’s immensely important to know more about emission dipole of observed perovskites.
[00:01:41.508]To do this, the angular distribution of emitted light was simulated using Python
[00:01:48.860]as well as some additional libraries such as NumPy, SciPy, all in the Jupyter Notebook environment.
[00:01:54.916]This allows for the simulation’s parameters to be changed relatively easily as compared to an experimental setup
[00:02:01.530]and for a large number of inputs to be evaluated.
[00:02:04.072]In doing so, we’ll create the core model for our future experimental study.
[00:02:08.942]A model was built so simulate the emission patters of single crystals of perovskites
[00:02:12.942]as based on previous modeling with respect to single molecule spectroscopy
[00:02:16.942]by Lieb et. al.
[00:02:18.452]These emission patterns are tied to the orientation of a crystal's dipole.
[00:02:22.452]In order to think about this, we can take the simplest example, shown here.
[00:02:26.452]The dipole has a positive end and a negative end. As a dipole oscillates
[00:02:32.912]which means the positive and negative charges become more or less stronger
[00:02:36.946]or separated, electromagnetic waves, like visible light are emitted in all
[00:02:40.946]directions perpendicular to the dipole.
[00:02:43.534]In our simulations, the dipole's orientation is critical to calculating the
[00:02:47.534]overall emission pattern.
[00:02:49.174]The dipole's orientation is described by two angles, phi, the polar angle,
[00:02:52.904]and theta, the azimuthal angle.
[00:02:56.631]In this figure, we're looking at the simulated emission pattern of a
[00:02:59.626]horizontal dipole, as you can see here.
[00:03:02.707]It's parallel to the Fourier plane, so the emitted light appears in lobe-like
[00:03:06.270]features, just as shown in the simple 2-D dipole example, albeit that example
[00:03:10.270]is much more zoomed in.
[00:03:13.000]In a vertical dipole, though, circular symmetry is observed,
[00:03:16.617]as the light is emitted perpindicular to the dipole.
[00:03:20.163]This gets much more complex with other orientations,
[00:03:22.917]and this is where the simulations become much more useful.
[00:03:26.057]Through simulating many orientations and comparing experimental emission
[00:03:30.057]patterns, it should be possible to figure out the orientation of the dipole being
[00:03:34.057]observed, based on how the angular distribution matches.
[00:03:37.545]As you can see here, this oblique dipole
[00:03:40.006]doesn't exactly have circular symmetry, as shown by this light area here, and this darker area here.
[00:03:46.219]And thus, an experimental emission pattern like this would need to be compared
[00:03:51.219]against a large number of possible patterns in order to discern the emission
[00:03:55.219]dipole of the observed crystal.
[00:03:57.315]The simulated angular distribution of emitted light will be critical in gaining
[00:04:01.111]information about the dipoles of perovskites that are observed through experimental spectroscopy.
[00:04:06.157]Along with the current application, the model can be expanded upon
[00:04:10.313]and improved in the future in order to simulate other systems.
[00:04:14.690]One clear pathway is the study of multiple layers of perovskites and accounting for
[00:04:18.490]in-plane and out-of-plane interactions between layers.
[00:04:22.382]By using these simulations to give context to future experimental data, we will
[00:04:26.382]hopefully give insight into developing more efficient and powerful optoelectronic devices.
[00:04:33.972]Alright. That is all I have. Thank you for listening to me talk about
[00:04:36.712]my research. I definitely appreciate it.

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Simulating Angular Distribution of Light in the Back Focal Plane: Emission Properties of Lead Halide Perovskites

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