Utkarsh Singh

Lead-free halide double perovskite (HDP) Cs2AgBiBr6 has set a benchmark for research in HDP photoelectric applications due to its attractive optoelectronic properties. However, its narrow absorption range is a key limitation of this material. Herein, a novel dopant, palladium (Pd), is doped into Cs2AgBiBr6 and significantly extends the absorption to ≈1400 nm. Pd2+ ions are partially doped in the host lattice, most probably replacing Ag atoms and introducing a sub-bandgap state within the host bandgap, as indicated by the combination of spectroscopical measurements and theoretical calculations. Importantly, this sub-bandgap state extends the photoresponse of Cs2AgBiBr6 up to the NIR-II region of 1300 nm, setting a new record for HDPs. This work demonstrates a novel and efficient dopant for HDPs and highlights the effectiveness of employing a sub-bandgap to broaden the absorption of HDPs, shedding new light on tailoring large bandgap HDPs for NIR optoelectronic applications.

Long-wavelength near-infrared light-emitting diodes (NIR LEDs) with peak emission wavelengths beyond 900\thinspacenm are of critical importance for various applications including night vision, biomedical imaging, sensing and optical communications. However, the low radiance and poor operational stability of state-of-the-art long-wavelength NIR LEDs based on soft materials remain the most critical factors limiting their practical applications. Here we develop NIR LEDs emitting beyond 900\thinspacenm with improved performance through the rational manipulation of p doping in all-inorganic tin perovskites (CsSnI3) by retarding and controlling the crystallization process of perovskite precursors in tin-rich conditions. The resulting NIR LEDs exhibit a peak emission wavelength at 948\thinspacenm, high radiance of 226\thinspaceW\thinspacesr−1\thinspacem−2 and long operational half-lifetime of 39.5\thinspaceh at a high constant current density of 100\thinspacemA\thinspacecm−2. Our demonstration of efficient and stable NIR LEDs operating at high current densities may also open up new opportunities towards electrically pumped lasers.

We have performed a comprehensive, first-principles high-throughput study of the magnetic properties of halide double perovskites, Cs2⁢BB′⁢Cl6, with magnetic ions occupying one or both B and B′ sites. Our findings indicate a general tendency for these materials to exhibit antiferromagnetic ordering with low Néel temperatures. At the same time, we reveal a few potential candidates that predicted to be ferromagnetic with relatively high Curie temperatures. Achieving ferromagnetic coupling might be feasible via simultaneously alloying at B and B′ sites with magnetic 3d and nonmagnetic 5d ions. With this approach, we discover that Cs2⁢HgCrCl6, Cs2⁢AgNiCl6, and Cs2⁢AuNiCl6 have high Curie temperatures relative to their peers, with the latter two exhibiting half metallic behavior. Further, this study illuminates the underpinning mechanism of magnetic exchange interactions in halide double perovskites, enabling a deeper understanding of their magnetic behavior. Our findings, especially the discovery of the compounds with robust half metallic properties and high Curie temperatures, hold promise for potential applications in the field of spintronics.

On the basis of purely their electronic properties, semiconducting alkali and alkaline earth metal based Heusler alloys have been identified as potentially promising thermoelectrics. Their thermal transport properties are decisive and help to further gauge this potential. This motivates us to systematically investigate lattice properties of three eight valence electron Heusler alloys, namely, Li2⁢NaSb, Na2⁢KSb, and K2⁢CsSb, using first-principles approaches. On the basis of both qualitative and quantitative descriptors (assessing covalent bonding, the atomic displacement parameter, the phonon density of states, the Grüneisen parameter, the phonon group velocity, and the phonon lifetime) we analyze in detail the lattice degrees of freedom and their contribution to thermal transport. Out of the three materials, Na2⁢KSb and K2⁢CsSb exhibit surprisingly low lattice thermal conductivity, which we can attribute to the anharmonic rattling of the loosely bound alkali atom in the crystal lattice. K2⁢CsSb has a lattice thermal conductivity two times lower than that of SnSe, a material with a record figure of merit.