Hybrid 2D Perovskite Could Push Into Graphene Territory
We’ve been spilling a lot of ink over perovskite solar cells here at CleanTechnica, and while the technology has a way to go before catching up with conventional silicon solar cells, the prospects are looking better almost by the minute. In the latest development, a research team at Lawrence Berkeley National Laboratory has claimed bragging rights to the first successful creation of a two-dimensional hybrid perovskite semiconductor made of ionic materials.
The research team anticipates initial applications in field-effect transistors and photodetectors. If the new hybrid finds its way into perovskite solar cells, it could give that “other” 2D material, graphene, a run for its money.
Perovskite And Solar Cells
For those of you new to the topic, perovskite refers to a class of minerals with a distinctive crystalline structure. The original, natural perovskite mineral was discovered in the Ural mountains in the 19th century, and since then various synthetic variations have been created, with the process being relatively simple and inexpensive compared to the manufacture of graphene.
As applied to solar cells, perovskite has some very attractive qualities. One obstacle hindering the adoption of first-generation perovskite solar cells is the use of lead, a toxic material. Work is progressing on developing lead-free versions, but that still requires the resolution of one serious drawback to perovskite — its tendency to break apart when exposed to humid air.
CleanTechnica happened to get one view on the future of perovskite solar cells during a recent technology tour of Switzerland, during a presentation by solar innovator Michael Graetzel. As Graetzel sees it, under the current state of technology, the most immediately productive path forward is to deploy the lead-based version only in utility settings where toxic materials can be more effectively contained, monitored, and eventually reclaimed or safely disposed.
In other words, don’t hold your breath for that nice new perovskite rooftop solar installation.
A 2D Path To More And Better Perovskite Solar Cells
We were just noticing that the 2D materials scene is getting rather crowded these days, and the new Berkeley Lab perovskite breakthrough illustrates how quickly the field is developing. The research is a product of the lab’s Molecular Foundry, a collaborative nanoscale research center organized by the Department of Energy.
You can continue holding your breath for distributed perovskite solar, because the new hybrid incorporates lead along with bromine, nitrogen, carbon, and hydrogen atoms. However, the research team points out that the ionic nature of its new 2D hybrid perovskite makes it stand out from other new 2D semiconductors materials, including boron nitride molybdenum disulfide, as well as graphene, due to its unique structure.
The other new 2D semiconductors are covalent, and if you recall your high school chemistry (we didn’t), ionic and covalent refer to two different kinds of bonds between atoms in a compound. As one reference point, solutions of ionic compounds conduct electricity, while covalent compounds do not.
Organic-inorganic hybrid perovskites in solution are already being used in thin film for solar cells, but unless somebody somewhere knows anything different, the Berkeley Lab material represents the first time that the hybrid materials have been successfully used in free-standing 2-D sheets.
Other attempts to create 2D perovskite sheets typically involve spin-coating, exfoliation, or chemical deposition among other methods, but the results have resulted in relatively thick panels. The Berkeley Lab team achieved the ultrathin 2D effect by “growing” crystals on a substrate, yielding these unique results:
“…a preliminary photoluminescence study indicates a band-edge emission at 453 nanometers, which is red-shifted slightly as compared to bulk crystals. This suggests that color-tuning could be achieved in these 2D hybrid perovskites by changing sheet thickness as well as composition via the synthesis of related materials.”
For all the details you can look up the study, “Atomically thin two-dimensional organic-inorganic hybrid perovskites,” in the journal Science.
Onwards And Upwards For Perovskites
The journal Nature Materials has a good overview of the promise and challenges of perovskites as of last year, including commentary by the aforementioned Michael Graetzel, but the field is evolving rapidly. Aside from the Berkeley Lab report, recent developments in the US include a lead free, semi-transparent, colorized perovskite solar cell developed by a team at Brown University. Perovskites also have potential application in electric vehicle battery technology, and sure enough earlier this year we scouted a rumor that a major global auto manufacturer was looking into a “disruptive” new perovskite electric vehicle battery.
If you’re guessing that auto maker was Tesla, good guess but no, unfortunately it was these guys.