Accelerated Discovery of Targeted Environmentally Friendly A(II)B(I)X3-Type Three-Dimensional Hybrid Organic-Inorganic Perovskites for Potential Light Harvesting via Machine Learning.

The engineered hybrid organic-inorganic perovskites (HOIPs) with outstanding multifunctionalities have realized overarching targeted-driven applications and thus aroused intense research interest. The emergence of three-dimensional (3D) A(II)B(I)X3-type HOIPs in 2018 brought a breakthrough to extend the 3D perovskite family and successfully realized prominent ferroelectricity at the same time. Here, we focus on these new-type HOIPs to perform machine-learning (ML)-based molecular design to screen promising candidates for versatile light harvesting, involving photovoltaics (77 ones), water splitting (216 ones), and photodetection (178 ones), out of 3180 A(II)B(I)X3 perovskites in total. These candidates await future experimental synthesis and characterization. Our high-throughput ML-based screening of 3D A(II)B(I)X3 HOIPs would enrich the material inventory by successfully introducing a class of new 3D HOIPs to realize property-oriented light harvesting and additional versatile energy harvesting due to their potential multifunctionalities such as ferroelectricity and electrocaloricity.

First-Principles Study on Out-of-Plane Piezoelectricity of Self-Assembled Ammonia Layers Confined in Two Vertically Stacked Graphene Oxide Nanosheets.

Two-dimensional (2D) piezoelectric materials have attracted widespread attention due to their increasingly important niche applications in flexible nanoscale devices. The water-wetted graphene oxide papers exhibit scalable out-of-plane piezoelectricity induced by the hydrogen-bonded network within, and this system can be treated as a potential 2D piezoelectric candidate for future device applications. It triggered our interest to search for more 2D piezoelectric hydrogen-bonded networks. Ammonia (NH3) isoelectronic with water is introduced to generate NH3-wetted graphene oxide papers and realize their out-of-plane piezoelectricity. Their structures and piezoelectricity are investigated using first-principles calculations. They reveal ultrahigh piezoelectricity, compared to the best reported 2D materials. Their piezoelectricity is tuned by varying oxygen-containing functional groups in GO plates, confined NH3 layers, or orientations of NH3 molecules, and it could be applied to fabrication of ammonia sensors. Our study not only enriches the family of 2D piezoelectric nanosystems but also inspires their future experimental exploration.

Self-assembled rhomboidal ammonia monolayer confined in two vertically stacked graphene oxide/graphene nanosheets.

Confined water molecules have attracted widespread research interest due to their versatile phase behaviors. Ammonia (NH3, isoelectronic with water) molecules are also expected to realize the delicate self-assembled hydrogen-bonded network like water in confinement. Here, the structures and phase behavior of NH3 monolayers confined in two structurally symmetrical graphene oxide (GO) or graphene (G) nanosheets are investigated using first-principles calculations and ab initio molecular dynamics simulations. A highly ordered new rhomboidal phase with all NH3 molecules adopting a Y-shaped configuration, in which one N-H bond is parallel to the confining planes and two other N-H bonds point to the top/bottom GO/G layers, respectively, was discovered at low temperature, resulting from the symmetrical confinement and subtle interlayer/intermolecular interactions. Remarkably, this new phase is so stable that a quite large strain is needed to destroy it. At room temperature, these NH3 monolayers behave like a liquid. These rhomboidal NH3 monolayers confined in GO/G nanosheets not only offer diverse hydrogen-bonded networks but also possess potential piezoelectricity for future device applications.