Two new polymorphs of piroxicam (Forms VI and VII) were discovered by melt crystallization and crystal structure prediction (CSP). High-quality single crystals were grown from melt microdroplets for structural solution by X-ray diffraction. Relative to the previously known polymorphs obtained mainly by solution crystallization, the new polymorphs are thermodynamically less stable, confirming melt crystallization as an important complement to solution crystallization in polymorph discovery. Although early workers reported that piroxicam is thermally unstable and unsuitable for melt crystallization, our use of melt microdroplets circumvented this problem because of the short exposure to a high temperature. Our CSP identified all known polymorphs of piroxicam including the two new forms with an energy ranking in reasonable agreement with the observed order, as well as low-energy structures not observed by experiment.

Perovskite solar cells (PSCs) have made unprecedented progress in improving power conversion efficiency in the past decade, and they are considered as one of the most promising photovoltaic technologies. However, the commercialization of PSCs still faces significant challenges, such as the stability issue and toxicity of lead. Recently, pursuing ways to alleviate the toxicity of lead has emerged as an attractive research direction in the community of PSCs. In this review, the discussion is on the toxicity of lead and the impact of lead leakage from perovskites to the environment, the recent progress made to reduce the leakage of lead is presented with an emphasis on the lead sequestration materials applied in encapsulation layers and functional layers of PSCs, and the recovery of lead from damaged or decommissioned PSC devices is concisely summarized. This review may serve as a guide for researchers interested in promoting PSCs from exploitation to application.

Polymorphism, the ability of the same substance to crystallize in more than one crystal structure, is a common phenomenon in organic crystals, influencing the physicochemical properties of solid materials in many important fields (foods, dyes and pigments, high energic materials, pharmaceuticals, etc.). The utilization of various polymorph discovery methods could increase the possibility of finding polymorphs with desired properties, achieving an optimal performance of the final product. Recently, there has been a steady development of polymorph discovery in both experimental and computational methods. To better guide the polymorph discovery, this paper reviews the recent advances in the polymorph screening methods of organic crystals, mainly including solution crystallization, melt crystallization, and crystal structure prediction. This paper also summarizes the nucleation theory in polymorphic systems to understand the formation of polymorphs and highlights the mechanisms of polymorph discovery by the kinds of methods. Finally, challenges of polymorph discovery are briefly discussed, aimed to shorten the screening time and make the polymorph discovery more effective.

Recently, favipiravir, as a broad-spectrum antiviral drug, has gain more attention because it might be a candidate to remedy the coronavirus disease 2019 (COVID-19). To improve its poor permeability and tabletability, four multicomponent crystals of favipiravir (FPV) were prepared by a slow evaporation or liquidassisted grinding method, including three cocrystals (FPVtheophylline, 1:1; FPV-saccharin, 1:1; FPV-5-fluorouracil, 1:1) and one salt (FPV-piperazine, 2:1). All of the crystal structures were solved by single-crystal X-ray diffraction. Interestingly, FPVtheophylline has a crystal structure similar to that of FPV, leading to similar properties, such as solubility, permeability, and tabletability. Except for FPV-theophylline, all of the other multicomponent crystals exhibit an enhanced permeability and tabletability. Our studies provide a new insight in overcoming the shortcomings of the important antiviral drug FPV.