Nanoconfined Metal Halide Perovskite Crystallization with Removable Polymer Scaffolds

Nanoconfined crystallization, a method to control the formation of specific polymorphs and crystal orientations, typically involves creating nanoporous scaffolds prior to nanopore filling with target compounds. While nanoporous scaffolds are effective for manipulating crystallization across various materials, this method typically results in largely inaccessible, isolated nanocrystals within electrically insulating scaffolds. Typical crystal-scaffold composites for optoelectronics are thus limited in optoelectronic applications which require large active surface areas for photophysical processes. Here we reverse the order of fabricating crystal-scaffold composites by first electrospinning interconnected networks of metal halide perovskite MAPbI3 precursor nanofibers, then subsequently introducing a poly(methylmethacrylate) (PMMA) scaffold by spin coating from solution using an antisolvent for MAPbI3. Nanofibers were converted to semiconducting MAPbI3 by thermal annealing the fibers in the presence and absence of PMMA. Annealing electrospun fibers without the confining PMMA scaffold resulted in large MAPbI3 crystals protruding from the fiber surfaces. Thermal annealing in the presence of the PMMA scaffold resulted in suppressed MAPbI3 blooming from the fiber surfaces. For these fibers, small, densely packed MAPbI3 crystals within the fibers were visible via transmission electron microscopy. Near infrared photodetectors using a coplanar electrode geometry revealed a percolated charge transport network in MAPbI3 fiber-PMMA scaffold composites, with external quantum efficiencies as high as 79%, compared to 1.2% for photodetectors comprising of non-infiltrated MAPbI3 fibers. MAPbI3 fiber-PMMA scaffold composites also exhibited significantly improved stability in air, indicating this strategy to be promising for metal halide perovskite-based optoelectronics.