Nanoscale Encapsulation of Hybrid Perovskites Using Hybrid Atomic Layer Deposition.

Organic-inorganic hybrid perovskites have shown tremendous potential for optoelectronic applications. Ion migration within the crystal and across heterointerfaces, however, imposed severe problems with material degradation and performance loss in devices. Encapsulating hybrid perovskite with a thin physical barrier can be essential for suppressing the undesirable interfacial reactions without inhibiting the desirable transport of charge carriers. Here, we demonstrated that nanoscale, pinhole-free Al2O3 layer can be coated directly on the perovskite CH3NH3PbI3 using atomic layer deposition (ALD). The success can be attributed to a multitude of strategies including surface molecular modification and hybrid ALD processing combining the thermal and plasma-enhanced modes. The Al2O3 films provided remarkable protection to the underlying perovskite films, surviving by hours in solvents without noticeable decays in either structural or optical properties. The results advanced the understanding of applying ALD directly on hybrid perovskite and provided new opportunities to implement stable and high-performance devices based on the perovskites.

Atomic Properties of Monoclinic Ag2Se Thin Film Grown on SrTiO3 Substrate by Molecular Beam Epitaxy.

Silver chalcogenides have attracted a great deal of interest due to their promise for exhibiting novel topological properties. Using scanning tunneling microscopy/spectroscopy (STM/S), we have characterized the atomic structure and electronic properties of a monoclinic Ag2Se thin film, similar to ß-Ag2Te, grown on a SrTiO3 (STO)(001) substrate by molecular beam epitaxy (MBE). Three different types of Ag2Se atomic terminations are observed on the surface: (i) homogeneous hexagonal-like, (ii) rough mixed, and (iii) flat zigzag-striped structures. Structural analysis indicates that the different atomic terminations stem from different growth directions, which can be attributed to the lattice mismatch between the substrate and the Ag2Se film. STS analysis of these atomic terminations uncovers different features near the Fermi level, indicating constituent- and direction-dependent electronic properties. This Letter presents a practical method to grow monoclinic thin film Ag2Se and provides insight into its physical properties.