Scaffold-Guided Crystallization of Oriented α-FAPbI3 Nanowire Arrays for Solar Cells

Nanoconfined Metal Halide Perovskite Crystallization within Removable Polymer Scaffolds

Nanoconfining crystallization to access metastable polymorphs and prescribe crystal orientations typically involves filling inert nanoporous scaffolds with target compounds, resulting in isolated nanocrystals. Such crystal-scaffold composites are unsuitable for optoelectronic devices that require interconnected crystalline pathways for charge transport. Here, we reverse the order of fabricating crystal-scaffold composites by first electrospinning interconnected networks of amorphous methylammonium lead iodide (MAPbI3) precursor nanofibers, then introducing a poly(methyl methacrylate) (PMMA) scaffold by spin coating from an antisolvent for MAPbI3. PMMA suppresses MAPbI3 crystal blooming from the fiber surface during thermal annealing, instead promoting the formation of densely packed polycrystalline networks of MAPbI3 crystals at the fiber/PMMA interface. Near-IR photodetectors comprising densely packed MAPbI3 nanocrystals grown within a PMMA scaffold in a coplanar electrode geometry exhibit photocurrents up to 60 times larger than those comprising fibers annealed without PMMA. These results indicate that MAPbI3 crystals form a percolated network for charge carriers to flow through PMMA-confined fibers, resulting in significantly improved photodetector performance.

Electrodeposition-Grown Mixed-Halide Inorganic Perovskite CsPbI3-xBrx Nanowires for Nanolaser Applications

Exploring new low-cost and controllable synthesis methods for perovskite nanowires plays an important role in achieving their large-scale applications. However, there have been no studies on the synthesis of cesium lead halide nanowires using the electrodeposition method. In this study, the single-crystal mixed-halide W-CsPbI3-xBrx nanowires are first synthesized via a low-cost and controllable electrodeposition method. The growth process of the W-CsPbI3-xBrx nanowires is observed in situ by using a metallurgical microscope. It is found that the W-CsPbI3-xBrx nanowires are grown via the oriented attachment of B-CsPbI3-xBrx nanocubes. More importantly, the mixed-halide W-CsPbI3-xBrx nanowires can transform into single-crystal B-CsPbI3-xBrx nanowires at a moderate annealing temperature. The obtained B-CsPbI3-xBrx nanowires are applied to nanolasers, and two lasing peaks are observed at 679 and 675 nm, with a threshold of 277.6 µJ cm-2. These results can promote the development of growth methods for perovskite nanomaterials, which can broaden the applicability of perovskite nanowires in integrated nanophotonic and optoelectronic devices.

Leveling up Organic Semiconductors with Crystal Twisting

The performance of crystalline organic semiconductors depends on the solid-state structure, especially the orientation of the conjugated components with respect to device platforms. Often, crystals can be engineered by modifying chromophore substituents through synthesis. Meanwhile, dissymetry is necessary for high-tech applications like chiral sensing, optical telecommunications, and data storage. The synthesis of dissymmetric molecules is a labor-intensive exercise that might be undermined because common processing methods offer little control over orientation. Crystal twisting has emerged as a generalizable method for processing organic semiconductors and offers unique advantages, such as patterning of physical and chemical properties and chirality that arises from mesoscale twisting. The precession of crystal orientations can enrich performance because achiral molecules in achiral space groups suddenly become candidates for the aforementioned technologies that require dissymetry.