These past weeks, I have finally created mixed 2D/3D perovskites with the correct phase, similar to ones found in literature! One of the new changes to the experimental procedure was making one of the precursor chemicals, the butylammonium iodide (BAI), ourselves rather than buying it. The process of homemaking the BAI is actualy quite time-consuming and requires lots of patience. However, it was a super cool experience since as a materials science major, I don't have that many opportunites to perform chemical synthesis procedures. Learning how to use the rotary evaporator and the Schlenk line was such a cool experience! Essentially, synthesizing the BAI involves mixing correct proportions of hydroiodic acid, butylamine, and ethanol, and then repeatedly drying, dissolving, and recrystallizing the product until it is pure enough. Although this additional step of homemaking the chemical takes a significant amount of time, it seems to be an important part of the experimental process for making perovskites (many papers I have read seem to also home-make their chemicals). The real challenge involved in synthesizing the BAI is finding all the equipment needed for the procedure, as the equipment is scattered across many lab benches!
One of my next goals is creating similar mixed 2D/3D perovskites, but with bromine instead of iodine as the halide. Since synthesizing the BAI has been so successful, I have also begun synthesizing the butylammonium bromide (BABr) which will be necessary for the bromine perovskites. The procedure is essentially identical and only involves changing the proportion of acid in the beginning (as hydrobromic acid is being used rather than hydroiodic acid). Once the BABr is ready to go, I can begin creating and characterzing the bromine 2D/3D perovskites and check if they match literature results as well!
In addition to making the bromine perovskites, I will also be looking into the stability of the mixed 2D/3D perovskites (both bromine and iodine). There are a couple of different ways to go about this, but the plan is currently to make a batch of the perovskite samples (with each batch consisting of multiple samples, each sample with varying amounts of BAX, X = I, Br). After the perovskites have been annealed and fully formed, I will leave one set in the desccicator and another set in a moisture-controlled environment, and use x-ray diffraction (XRD) to monitor the degradation of the perovskites. Since the peak locations in XRD plots are used to determine the phase, I will mainly be watching for any changes in relative intensities and/or locations of the peaks. Since the perovskites are composed of BAX:MAPbX3 (X = I, Br), as they degrade PbX3 should begin to show up in the XRD plots. This is the peak I will definitely be watching out for. Also, the color of the perovksites should change as well since the perovskite's color is different than the precursor chemicals' colors. Hopefully I find that samples with increasing amounts of BAX (increasingly 2D) degrade slower! In terms of applications, since one of the goals for perovskites is to be used in solar cells, the stability of the perovskites is extremely important. As of right now, they are not quite stable enough to compete with silicon-based solar cells, which is why research into the thermal stability and moisture-resistance of new kinds of perovskites is important.
A slight challenge with the current plan to test the stability is that there is no moisture-controlled environment currently in the lab. I don't doubt that there is some equipment that exists and probably can pump water vapor into a sealed box where you can store samples. However, since this equipment does not exist in the current lab, I am discussing with Dr. Sutter-Fella and looking into other ways to improvise this setup. One potential idea involves using a sealed nitrogen tent (essentially a nitrogen glovebox but smaller), and leaving beakers of water to modify the relative humidity. The plans for this are still in the works, but hopefully by my next blog post, I will have some results from this perovskite stability study!
Lastly, a quick shoutout to the LBNL security and protective services for finding my lost wallet! I lost it on a lab shuttle about a week ago, and they managed to return it to me with everything still inside (even the cash)!