Phosphorus-Ligand Redox Cooperative Catalysis: Unraveling Four-Electron Dioxygen Reduction Pathways and Reactive Intermediates.

The reduction of dioxygen to water is crucial in biology and energy technologies, but it is challenging due to the inertness of triplet oxygen and complex mechanisms. Nature leverages high-spin transition metal complexes for this, whereas main-group compounds with their singlet state and limited redox capabilities exhibit subdued reactivity. We present a novel phosphorus complex capable of four-electron dioxygen reduction, facilitated by unique phosphorus-ligand redox cooperativity. Spectroscopic and computational investigations attribute this cooperative reactivity to the unique electronic structure arising from the geometry of the phosphorus complex bestowed by the ligand. Mechanistic study via spectroscopic and kinetic experiments revealed the involvement of elusive phosphorus intermediates resembling those in metalloenzymes. Our result highlights the multielectron reactivity of phosphorus compound emerging from a carefully designed ligand platform with redox cooperativity. We anticipate that the work described expands the strategies in developing main-group catalytic reactions, especially in small molecule fixations demanding multielectron redox processes.

Ferroelectric-mediated filamentary resistive switching in P(VDF-TrFE)/ZnO nanocomposite films.

In ferroelectric (FE) polymer-semiconducting polymer blend based organic resistive random access memory devices (ReRAM), the carriers are injected into the semiconductor region of the blend because of the polarization originated internal electric field in the FE polymer. A higher concentration of semiconducting polymer in the FE polymer-semiconducting polymer blends usually generate a high leakage current and degrades the FE characteristics of the FE polymer resulting in a high OFF current and consequently a low ON/OFF ratio. In order to achieve a high ON/OFF ratio in the FE polymer/semiconducting polymer blends, the FE properties of the FE polymer should be preserved. In this study, organic ReRAMs based on ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and ZnO nanoparticle (NPs) blends exhibiting bipolar resistive switching and a high ON/OFF ratio were realized using a low-cost solution process. Unlike conventional ferroelectric polymer-semiconducting polymer blend systems where FE characteristics are suppressed in ReRAMs, our Au/P(VDF-TrFE)_ZnO NPs/n++Si devices retain the FE characteristics of the P(VDF-TrFE) polymers. Our devices switch between bi-stable resistance states via the ferroelectric-assisted filamentary conduction mechanism. Based on ex situ transmission electron microscopy and elemental mapping analyses, we found that the resistive switching occurs through the formation of conduction paths consisting of Zn-rich/F-deficient regions. The device fabricated at a blend ratio of 20 wt% ZnO NPs in P(VDF-TrFE) matrix exhibited optimal stable resistive switching behavior with an ON/OFF ratio of up to 2 × 107 and a retention time of 104 s.

Improvement of perovskite crystallinity by omnidirectional heat transfer via radiative thermal annealing.

As promising photo-absorbing materials for photovoltaics, organic-inorganic hybrid perovskite materials such as methylammonium lead iodide and formamidinium lead iodide, have attracted lots of attention from many researchers. Among the various factors to be considered for high power conversion efficiency (PCE) in perovskite solar cells (PSCs), increasing the grain size of perovskite is most important. However, it is difficult to obtain a highly crystalline perovskite film with large grain size by using the conventional hot-plate annealing method because heat is transferred unidirectionally from the bottom to the top. In this work, we presented radiative thermal annealing (RTA) to improve the structural and electrical properties of perovskite films. Owing to the omnidirectional heat transfer, swift and uniform nuclei formation was possible within the perovskite film. An average grain size of 500 nm was obtained, which is 5 times larger than that of the perovskite film annealed on a hot-plate. This perovskite film led to an enhancement of photovoltaic performance of PSCs. Both short-circuit current density and PCE of the PSCs prepared by RTA were improved by 10%, compared to those of PSCs prepared by hot-plate annealing.