One-step vapour phase growth of two-dimensional formamidinium-based perovskite and its hot carrier dynamics.

Formamidinum lead iodide perovskite is one of the most promising materials for application in solar cells due to its narrow band gap and higher thermal stability. In this work, we demonstrate the facile synthesis of square-shaped formamidinium lead iodide single crystals on indium tin oxide (ITO) substrates using a one-step vapour phase deposition method. Formamidinium lead iodide-based two-dimensional layered perovskite crystals were successfully synthesized by controlling the deposition conditions. These crystals exhibited a blue-shifted photoluminescence (PL) compared to the conventional formaminium lead iodide perovskite crystals. Power law fittings of the excitation power dependent PL spectra revealed that Auger heating becomes dominant at high excitation densities. In addition, we observed an asymmetric broadening of the PL peak tail at the high energy side, indicating light emission from hot carriers even under steady-state illumination conditions. Phonon-bottleneck effect and Auger heating were considered as the main mechanisms for retardation of hot carrier cooling. Further analysis of the high energy tails using Maxwell-Boltzmann fitting revealed hot-carrier temperatures as high as 690 K. Our findings provide an important aspect of the synthetic approach of perovskites for their potential application in hot carrier solar cells.

Vapor Phase Selective Growth of Two-Dimensional Perovskite/WS2 Heterostructures for Optoelectronic Applications.

Organic-inorganic hybrid perovskites have attracted increased interest owing to their exceptional optoelectronic properties and promising applications. Monolayers of transition metal dichalcogenides (TMDCs), such as tungsten disulfide (WS2), are also intriguing because of their unique optoelectronic properties and their atomically thin and flexible structures. Therefore, the combination of these different types of materials is very attractive in terms of fundamental science of interface interaction, as well as for the realization of ultrathin optoelectronic devices with high performance. Here, we demonstrate the controlled synthesis of two-dimensional (2D) perovskite/WS2 heterostructures by an all vapor-phase growth approach. This involves the chemical vapor deposition (CVD) growth of monolayer WS2, followed by the vapor-phase selective deposition of 2D PbI2 onto the WS2 with the successive conversion of PbI2 to organic-inorganic perovskite (CH3NH3PbI3). Moreover, the selective growth of the perovskite on prepatterned WS2 enables the direct synthesis of patterned heterostructures, avoiding any damage to the perovskite. The photodetectors utilizing the perovskite/WS2 heterostructure show increased responsivities compared with isolated thin perovskite obtained by conventional solution methods. The integration of 2D perovskite with TMDCs opens a new avenue to fabricate advanced devices by combining their unique properties and overcoming current processing difficulties of perovskites.

From 2-methylimidazole to 1,2,3-triazole: a topological transformation of ZIF-8 and ZIF-67 by post-synthetic modification.

Bridging ligand replacement in zeolitic imidazolate frameworks, ZIF-8 and ZIF-67, by 1,2,3-triazole was investigated. A complete substitution of 2-methylimidazole by 1,2,3-triazole resulted in a topological transformation of the parent framework from a sodalite (SOD) network to a diamond (DIA) network.