Formation of Ultimate Thin 2D Crystal of Pt in the Presence of Hexamethylenetetramine.

Platinum naturally crystalizes into a three-dimensional crystal due to its highly symmetrical fcc lattice, with a metallic bond which is non-directional and highly isotropic. This inherently means ultimately that 2D crystals of a few atoms thick growth are hardly available in this material. Here, we discovered that a combinative effect of formic acid reductant and hexamethylenetetramine surfactant during the reduction of their metal ions precursor can realize an ultimate thin 2D crystal growth in platinum. High-resolution transmission electron microscopy and filed-emission electron microscopy analysis have also discovered that the 2D crystal of Pt has 111 facets with a lateral dimension that can be up to more than 5 µm × 2 µm. The thickness of the 2D crystal of Pt is 1.55 nm. A mechanism for obtaining ultimate thin 2D crystal of Pt using the present approach is proposed.

Air-Processable Perovskite Solar Cells by Hexamine Molecule Phase Stabilization.

Perovskite solar cells have emerged as a potential energy alternative due to their low cost of fabrication and high power conversion efficiency. Unfortunately, their poor ambient stability has critically limited their industrialization and application in real environmental conditions. Here, we show that by introducing hexamine molecules into the perovskite lattice, we can enhance the photoactive phase stability, enabling high-performance and air-processable perovskite solar cells. The unencapsulated and freshly prepared perovskite solar cells produce a power conversion efficiency of 16.83% under a 100 mW cm-2 1.5G solar light simulator and demonstrate high stability properties when being stored for more than 1500 h in humid air with relative humidity ranging from 65 to 90%. We envisage that our findings may revolutionize perovskite solar cell research, pushing the performance and stability to the limit and bringing the perovskite solar cells toward industrialization.

Optoelectrical Properties of Hexamine Doped-Methylammonium Lead Iodide Perovskite under Different Grain-Shape Crystallinity.

The crystallinity properties of perovskite influence their optoelectrical performance in solar cell applications. We optimized the grain shape and crystallinity of perovskite film by annealing treatment from 130 to 170 °C under high humidity (relative humidity of 70%). We found that the grain size, grain interface, and grain morphology of the perovskite are optimized when the sample was annealed at 150 °C for 1 h in the air. At this condition, the perovskite film is composed of 250 nm crystalline shape grain and compact inter-grain structure with an invincible grain interface. Perovskite solar cells device analysis indicated that the device fabricated using the samples annealed at 150 °C produced the highest power conversion efficiency, namely 17.77%. The open circuit voltage (Voc), short-circuit current density (Jsc), and fill factor (FF) of the device are as high as 1.05 V, 22.27 mA/cm2, and 0.76, respectively. Optoelectrical dynamic analysis using transient photoluminescence and electrochemical impedance spectroscopies reveals that (i) carrier lifetime in the champion device can be up to 25 ns, which is almost double the carrier lifetime of the sample annealed at 130 °C. (ii) The interfacial charge transfer resistance is low in the champion device, i.e., ~20 Ω, which has a crystalline grain morphology, enabling active photocurrent extraction. Perovskite's behavior under annealing treatment in high humidity conditions can be a guide for the industrialization of perovskite solar cells.