State-of-the-art halide perovskite solar cells have bandgaps larger than 1.45 eV, which restricts their potential for realizing the Shockley-Queisser limit. Previous search for lowbandgap (1.2 to 1.4 eV) halide perovskites has resulted in several candidates, but all are hybrid organic-inorganic compositions, raising potential concern regarding device stability. Here we show the promise of an inorganic low-bandgap (1.38 eV) CsPb 0.6 Sn 0.4 I 3 perovskite stabilized via interface functionalization. Device efficiency up to 13.37% is demonstrated. The device shows high operational stability under one-sun-intensity illumination, with T 80 and T 70 lifetimes of 653 h and 1045 h, respectively (T 80 and T 70 represent efficiency decays to 80% and 70% of the initial value, respectively), and long-term shelf stability under nitrogen atmosphere. Controlled exposure of the device to ambient atmosphere during a long-term (1000 h) test does not degrade the efficiency. These findings point to a promising direction for achieving low-bandgap perovskite solar cells with high stability.

Halide perovskite semiconductors exhibit ultralow thermal conductivities, making them potentially suitable for thermoelectric applications. Nevertheless, the thermoelectric properties of the prototypical halide perovskite of CH 3 NH 3 PbI 3 have been limited with a very low dimensionless figure of merit (ZT) and a narrow operating temperature window, which are attributed to its poor electronic conductivity and unstable hybrid organic−inorganic composition, respectively. Here, we report the bulk synthesis of a stable, all-inorganic halide perovskite of CsSn 0.8 Ge 0.2 I 3 as a new thermoelectric material, which shows a 10 order of magnitude enhancement in ZT compared with that of CH 3 NH 3 PbI 3 and an operating temperature as high as 473 K. Importantly, this CsSn 0.8 Ge 0.2 I 3 perovskite is also Pb-free in the composition, attesting its high potential as an environmentally friendly candidate material for future thermoelectrics.

In this work, RENbO4 (RE = Y, La, Nd, Sm, Gd, Dy, Yb) ceramics with low density, low Young's modulus, low thermal conductivity, and high thermal expansion have been systematically investigated, the excellent thermo‐mechanical properties indicate that RENbO4 ceramics possess the potential as the new generation of thermal barrier coatings (TBCs) materials. X‐ray diffraction and Raman spectroscopy phase structure identification reveal that all dense bulk specimens obtained by high‐temperature solid‐state reaction belonged to the monoclinic (m) phase with C12/c1 space group. The ferroelastic domains are detected in the specimens, revealing the ferroelastic transformation between tetragonal (t) and monoclinic (m) phases of RENbO4 ceramics. The Young's modulus and hardness of the RENbO4 ceramics measured by the NanoBlitz 3D nanoindentation method are discussed in details, and the lower Young's modulus (60‐170 GPa) and higher hardness (the maximum value reaches 11.48 GPa) indicating that higher resistance of RENbO4 ceramics to failure and damage. Lower thermal conductivity (1.42‐2.21 W [m k]−1 at 500°C‐900°C) and lower density (5.330‐7.400 g/cm3) than other typical TBCs materials give RENbO4 ceramics the unique advantage of being new TBCs materials. Meanwhile, the thermal expansion coefficients of RENbO4 ceramics reach 9.8‐11.6 × 10−6 k−1 and are comparable or higher than other typical TBCs materials. According to the first‐order derivative of the thermal expansion rate, the temperature of the ferroelastic transformation of RENbO4 ceramics can be observed.

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In this work, the dense bulk polymorphous YTaO4 ceramics with M or M' phase are synthesized by spark plasma sintering method accompanying with different tempering procedures. Combined with the nano‐indentation and theoretical calculation, their mechanical properties are systematically investigated. The identification of crystal structure reveals that the YTaO4 crystallizes into M phase (space group: I2/a) with higher tempering temperature, otherwise it crystallizes into M' phase (space group: P2/a). The results of mechanical properties indicate M‐phase YTaO4 possesses larger Young's modulus and hardness than that of M' phase. It is stemmed from the chemical bonding strength of M phase is stronger than that of M' phase, and the stronger bonding strength of M phase also results in its elastic resilience is superior to M' phase. Besides, on account of the low symmetry of monoclinic crystal system, the Young's modulus of polymorphous YTaO4 ceramics exhibit strong anisotropy.

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The super low thermal conductivity and ultrahigh thermal expansion of Ba6Ln2Al4O15 (Ln = Gd, Dy, Er, and Yb) compounds with one‐sixth of the oxygen vacancy have been synthesized by the solid‐state reaction method. The lowest thermal conductivity of Ba6Yb2Al4O15 was found to be 0.98 W/(m.K) at 1073 K. The large concentration of oxygen vacancies in Ba6Ln2Al4O15 compounds leads to low elastic modulus and loose chemical bonds. The average thermal expansion coefficients of Ba6Ln2Al4O15 compounds was 11.8 × 10−6 ˜ 13.6 × 10−6 · K−1. The loose chemical bonds with Young's moduli were in the range of 102.8 ˜ 135.9 GPa.