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Lead halide perovskites have gained more and more attention because of their ease of synthesis and excellent photoelectric properties including a large absorption coefficient, long carrier lifetime, long carrier diffusion length, and high carrier mobility. However, their toxicity, instability, and phase degradation in ambient environments impede their large-scale applications. To address these concerns, it is desirable to find stable alternative halide perovskites without toxicity and with comparable optoelectronic properties to lead-based perovskites. Over the years, a considerable number of lead-free halide perovskites have been added to this family of materials, including A2B’B’’X6, A2BX6, and A3B2X9 type perovskites. Among these, double perovskites with the general formula A2B’B’’X6 are deemed to be a potential alternative to lead halide perovskites as they possess good stability under ambient conditions and excellent optoelectronic properties. In this review, recent progress in exploring Pb-free halide double perovskites is highlighted. The synthesis, composition-tuning, physical properties, and applications of representative 3D, 2D, and nanocrystal A2B’B’’X6 double perovskites are introduced. In addition, perspectives about current challenges and solutions in this field are also provided.

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Poly(N‐isopropylacrylamide‐co‐acrylic acid) [p(NiPA‐co‐AAc)] microgel particles were synthesized by free radical precipitation polymerization in aqueous medium. Silver nanoparticles (Ag NPs) were fabricated inside the microgels by in situ reduction method. UV–visible, Fourier transform infrared (FTIR), and dynamic light scattering techniques were used for characterization of pure microgels. The Ag‐p(NiPA‐co‐AAc) hybrid microgels were characterized by UV–visible, FTIR, X‐ray diffraction, and transmission electron microscopy. The hybrid microgel system was used as a catalyst for reduction of 4‐nitroaniline (4‐NA) in aqueous medium. The kinetics of the catalytic reduction of 4‐NA under various conditions of concentration of hybrid microgels, sodium borohydride (NaBH4), and 4‐NA was monitored by UV–visible spectrophotometry. It was found that the value of apparent rate constant (kapp) increases with increase of concentration of NaBH4 and catalyst dosage while it remains constant at various concentrations of 4‐NA. The kinetic data were used to elaborate the conversion of 4‐NA into p‐phenylenediamine on the basis of electron relaying effect of Ag NPs present inside the microgels. POLYM. COMPOS., 39:645–653, 2018. © 2016 Society of Plastics Engineers

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