Although SrTiO3-based perovskites showed a lot of promise as n-type thermoelectric (TE) materials, they demonstrated a low figure of merit value primarily because of their high lattice thermal conductivity (k l). Researchers found it difficult to reduce k l, as a popular route like nanostructuring did not work well with these perovskites possessing low phonon mean free paths. Here, we put forward a novel strategy of designing high-entropy perovskite (HEP) oxides having five transition metals in the B site to induce more anharmonicity causing enhanced multiphonon scattering in order to decrease k l. Using detailed thermodynamic calculations, we designed and synthesized a highly dense Sr­(Ti0.2Fe0.2Mo0.2Nb0.2Cr0.2)­O3 HEP ceramic. An ultralow thermal conductivity of 0.7 W/mK at 1100 K was achieved in this n-type rare-earth-free HEP oxide TE material. The concept of designing HEPs to achieve ultralow thermal conductivity potentially opens up a new avenue for enhancing TE performance of environmentally benign bulk oxides for high-temperature TE power generation.

Quantum-confined two-dimensional (2D) Ruddlesden–Popper (RP) perovskite nanoplates (NPls) are drawing considerable attention in recent times. The effect of external perturbations like air, moisture, heat, polarity of the solvent, and, specifically, light irradiation has significant impact on the RP perovskite structure in different ways. Though some reports are available on the effect of light irradiation on RP NPl single crystals, films, and flakes, no comprehensive study is available for the RP NPl colloidal state. To extend the understanding, we studied the fate of UV irradiation on a colloidal, orange-emitting oleylammonium iodide-based RP NPl, (C18H35NH3)2(CH3NH3PbI3)2PbI4 (n = 3). A constant UV exposure for 10 h transforms the RP NPl structure into a purely 3D methylammonium lead iodide (CH3NH3PbI3, MAPbI3) nanorod (NR) having a photoluminescence quantum yield of 65%. Our experimental results reveal that this structural transformation takes place by ligand desorption, followed by structural association in an oriented fashion. The obtained MAPbI3 NR shows excellent optical and crystalline phase stability for more than 2 months.

The low photoluminescence quantum yield of Bi 3+ -doped lead halide perovskite nanocrystals (NCs) is a big challenge to the scientific community. This makes them a weak candidate in the optoelectronics field in spite of their better stability than the pure lead analogue. Herein, the reason behind this reduction of quantum yield in hybrid mixed lead−bismuth bromide (MPBBr) NC is investigated and proposed to be due to ultrafast trapping transfer in the core of the NC, and not due to the surface trap states. Further, we have successfully boosted the quantum yield of MPBBr NC from 9% to 64% by passivating the deep traps within the crystal core by monovalent potassium ion doping. The stability of the developed Bi 3+ /K + -doped lead halide perovskite NC was found to be extremely high in atmospheric conditions, and this property is sustained up to 100 °C.

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