Search

Hybrid organo-inorganic perovskites are a well-known material in the field of optoelectronic devices. They are easy to synthesize and scale, and due to the variability of composition, their properties are tunable. Until now, a significant problem in the use of this material is the environmental instability. Changing the composition of the layers by introducing copper complexes in place of an organic layer can help reduce the material degradation rate, change the optical properties, as well as add one more degree of freedom in their variability. The structure and phase transitions of hybrid perovskite with copper paddle-wheel clusters linking perovskite layers [Cu(O2C-(CH2)3-NH3)2]PbBr4 were investigated using Raman spectroscopy under variable pressure up to 17 GPa, furthermore in the temperature range between 80 K to 373 K. The following optical properties of the material are described: photoluminescence, the dependence of absorption on pressure. Primary DFT calculations have shown that the studied material can be considered as a three-component system in which energy transfers between components are possible. Based on them, further prospects for the study and application of copper-containing perovskite are proposed.

Two-dimensional (2D) phenylethyl ammonium (PEA+)-methyl ammonium (MA+) lead iodide ((PEA)2(MA)[Pb2I7]) hybrid perovskite exists as temperature-dependent dimorphs exhibiting an ill-defined phase transition occurring over the 150–200 K range. Raman scattering, photoluminescence, optical absorbance and solid state MAS NMR spectroscopic methods are employed to investigate the structural complexity, disorder and structure/function of this system. The Raman and 1H MAS NMR data indicate that the lower bounds of the phase transition at ∼150 K are characterised by attenuated rotational modes and slower motional dynamics throughout the disordered MA+ organic sublattice, inducing a strengthening of the MA+⋯I hydrogen bonds and a 5 meV increase in the excitonic and photoluminescence energies. It is evident that different recombination mechanisms are dominant for the room temperature and low temperature phases reflecting the importance of MA+ dynamics in the optical properties of the material. Single crystal X-ray studies are unable to position the organic cations within the Pb2I7 framework; however, 1H/13C MAS NMR measurements describe elements of local structural disorder based on conformational isomerism within the PEA+ sublattice. Concomitant I− and Pb2+ migration and [Pb2I7]3− framework defects create stacking disorder, dislocations and dispersed octahedral tilting leading to additional disorder and distributed MA+ and PEA+ cation dynamics.\ud \ud

A two-dimensional hybrid perovskite, (PEA)2PbI4, is added as a functional additive to a dielectric PVDF terpolymer matrix to improve its dielectric strength. It is found that a trace amount of added (PEA)2PbI4 of 0.1 wt% gives rise to a 25% improvement in the DC dielectric breakdown strength of the polymer. Mechanistic study using terahertz time-domain spectroscopy reveals that the perovskite additive reduces the carrier density in the polymer matrix correspondingly, which is believed to be the main reason that leads to a large breakdown strength enhancement. This work presents not only a novel potential application of a 2D hybrid perovskite, but also a practical approach to modify polymeric dielectric materials for the achievement of excellent electrical insulating performance.

We utilized two organic dications containing, respectively, a pyridinium and an imidazolium core to construct new n = 1 (where n refers to the number of contiguous two-dimensional (2D) inorganic layers, i.e., not separated by organic cations) 2D lead–iodide perovskites 1 and 2. The former material exhibits a (100)- and the latter a very rare 3 × 3 (110)-structural type. Compared with primary ammonium functionality, their constituent ring-centered positive charges have lower charge density. As a result, [PbI6]4– interoctahedral distortions of the inorganic lattice in 1 and 2 are reduced (Pb–I–Pb bond angles are as high as 166° and 174°, respectively). This results in bathochromically shifted optical features. In addition, the compact nature of the dications produces extremely short lead–iodide sheet separations, with respective iodide–iodide (I···I) distances as small as 4.149 and 4.278 Å. These are among the shortest separations of adjacent lead–iodide layers ever reported for such materials. When crystallized as thin films on top of substrates, the resulting 2D perovskite layers do not adopt a regular growth direction parallel to the surface. Instead, the crystallites grow with no fixed orientation. As a consequence of their proximate inorganic distances and unusual crystallization tendencies, the resulting 2D perovskites exhibit low excitonic activation energies (93.59 and 96.53 meV, respectively), enhanced photoconductivity in solar cells, and unprecedented incident photon-to-current conversion rates of up to 60%. More importantly, mesoporous 2D layered perovskite solar cells with power conversion efficiencies of 1.43 and 1.83% were achieved for 1 and 2, respectively. These are the highest values obtained thus far for pure n = 1 lead–iodide perovskites and more than 20 times higher than those obtained for materials templated by more conventional cations such as phenylethylammonium (0.08%). NRF (Natl Research Foundation, S’pore) Accepted version