Localized Heating Tailors Nucleation for Reproducible Growth of Thin Halide Perovskite Single Crystals

Halide perovskites (HaPs) are functional semiconductors that can be prepared in a simple, near-room-temperature process. With thin polycrystalline HaP films, excellent solar cells, light-emitting diodes (LEDs), and (also as single crystals) high-energy radiation detectors have been demonstrated. The very low single-crystal defect densities make HaP thin single crystals (TSCs), instead of polycrystalline HaP films an attractive option, to boost device performances and for fundamental research. However, growing TSCs is challenging primarily because of random multiple nucleations, which, in the often-used space-confined geometry, is favored at the substrate boundaries, where loss of organo-amines and solvents occurs. We show that fewer and better-quality thin crystals nucleate and grow reproducibly away from the substrate edges in the substrate center, if we localize the heating (needed for inverse-temperature crystallization, the preferred crystal growth method) there. Using a further finding of ours that lowers the crystallization temperature, TSCs of methylammonium lead bromide (MAPbEr(3)), the HaP we focus on here, grow also directly on flexible substrates. H-1 NMR measurements show how the observed lower crystallization temperature results from slow humidity-mediated chemical changes in the HaP precursor solution during its storage.

Automated summary

Halide perovskites (HaPs) are functional semiconductors that can be prepared in a simple, near-room-temperature process. Excellent solar cells, LEDs, and high-energy radiation detectors have been demonstrated using thin polycrystalline HaP films. To improve device performances and for fundamental research, thin single crystals (TSCs) are preferred due to their low defect densities. However, the challenge lies in the random multiple nucleations, which can be overcome by localizing the heating in the substrate center.