Halogenation is an effective way to tune the energy levels of organic semiconducting materials. To date, fluorination of organic semiconducting materials to fabricate polymer solar cells (PSCs) has been used far more than chlorination; however, fluorine exchange reactions suffer from low yields and the resulting fluorinated polymer always comes with a higher price, which will greatly hinder their commercial applications. Herein, we designed and synthesized a series of chlorinated donor–acceptor (D-A) type polymers, in which benzo­[1,2-b:4,5-b]­dithiophene and chlorinated benzothiadiazole units are connected by thiophene π-bridges with an asymmetric alkyl chain. These chlorinated polymers showed deep highest occupied molecular orbital (HOMO) energy levels, which promoted the efficiency of their corresponding PSCs by increasing the device open circuit voltage. The asymmetric alkyl chain on the thiophene moieties gave the final polymer sufficient solubility for solution processing and strong π–π stacking in films allowed for high mobility. Although the introduction of a large Cl atom increased the torsion angle of the polymer backbone, the chlorinated polymers maintained a favorable backbone orientation in blend films for efficient PSC application. These factors contributed to respectable device performances from thick-film devices, which showed PCEs as high as 9.11% for a 250-nm-thick active layer. These results demonstrate that chlorination is a promising method to fine-tune the energy levels of conjugated polymers, and chlorinated benzothiadiazole may be a versatile building block in materials for efficient solar energy conversion.

This study aims to investigate the crystallization behavior and molecular dynamics of amorphous griseofulvin (GSF) in the presence of low-concentration poly(ethylene oxide) (PEO). We observe that the addition of 3% w/w PEO remarkably increases the crystal growth rate of GSF by two orders of magnitude in both the supercooled liquid and glassy states. The liquid dynamics of amorphous GSF in the presence and absence of PEO are characterized by dielectric spectroscopy. With an increase of the PEO content, the α-relaxation times of the systems decrease, indicating the increase of global molecular mobility. The couplings between molecular mobility and crystallization kinetics of GSF systems show strong time-dependences below T. The overlapping of α-relaxation times of GSF in presence and absence of PEO as a function of T/T suggest the "plasticization" effect of PEO additives. However, the crystallization kinetics of amorphous GSF containing low-concentration PEO do not overlap with those of pure GSF on a T/T scale. The remarkable accelerating effect of crystal growth of amorphous GSF by low-concentration PEO can be partially attributed to the increase of global mobility. The high segmental mobility of PEO is expected to strongly affect the crystal growth rates of GSF. These findings are relevant for understanding and predicting the physical stability of amorphous pharmaceutical solid dispersions.

Griseofulvin (GSF) is a classic antifungal drug that has been in clinical use for over 50 years, but its polymorphism was recognized only recently via melt crystallization. Here we report the structure of a single crystal of GSF form II which was unusually harvested from the supercooled melt. GSF form II exhibits an anomalously large thermal expansion coefficient.

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