Inorganic halide perovskites such as cesium lead halide are promising due to their excellent thermal stability. Cesium lead iodide (CsPbI3) has a bandgap of 1.73 eV and is very suitable for making efficient tandem solar cells, either with low-bandgap perovskite or silicon. However, the phase instability of CsPbI3 is hindering the further optimization of device performance. Here, we show that high quality and stable α-phase CsPbI3 film is obtained via solvent-controlled growth of the precursor film in a dry environment. A 15.7% power conversion efficiency of CsPbI3 solar cells is achieved, which is the highest efficiency reported for inorganic perovskite solar cells up to now. And more importantly, the devices can tolerate continuous light soaking for more than 500 h without efficiency drop.

Bi- and Na-substituted Ca3Co4O9 polycrystalline samples have been prepared using a hot-pressing technique and their thermoelectric properties were carefully studied in air from room temperature to 1000 K. The substitutions of Bi3+ and Na+ for Ca2+, as well as Bi3+ and Na+ double substitution, cause both the electrical conductivity (σ) and thermoelectric power (S) to increase simultaneously. The double substitution has also been demonstrated to be effective to decrease the thermal conductivity (κ). The dimensionless figure of merit ZT (=S2σT/κ) reaches 0.32 at 1000 K in the double-substituted sample.

Quantitative texture analysis of grain-aligned [ Ca 2 Co O 3 ] 0.62 [ Co O 2 ] ceramics processed by the reactivetemplated grain growth method Highly grain-aligned Ca 3 Co 4 O 9 and (Ca 2.7 Sr 0.2 La 0.1 )(Co 3.9 Cu 0.1 )O 9 ceramics were prepared by the magnetic alignment technique, and then treated by a spark plasma sintering process to increase their bulk densities. Thermoelectric properties were investigated from room temperature to 700°C in air. Grain alignment is effective in lowering the electrical resistivity and has no obvious influence on the Seebeck coefficient, thus resulting in enhancement of the thermoelectric power factor. Substitution of Sr, La and Cu does not appreciably change the electrical resistivity and Seebeck coefficient, but significantly reduces the thermal conductivity.

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Polycrystalline samples of Bi2.2−xPbxSr2Co2Oy (x=0, 0.4, and 0.8) with a layered structure have been prepared using a hot pressing technique and their thermoelectric properties methodically investigated. It is found that the substitution of Pb for Bi is a fairly effective means of improving the thermoelectric properties of the Bi2.2−xPbxSr2Co2Oy system owing to resistivity (ρ) decreasing and thermoelectric power (S) increasing simultaneously. The thermal conductivity (κ) at high temperature also decreases markedly with Pb substitution. As a result, for the x=0.8 sample the dimensionless figure of merit, ZT(=S2T/ρκ), increases with temperature and reaches 0.26 at 1000 K, which indicates that this material is a strong candidate as a high-temperature thermoelectric material.