A nitrogen-doped graphene/sulfur composite was further modified with atomic layers of TiO2and used as the cathode of lithium–sulfur batteries, exhibiting superior cycling stability, good rate capability and high coulombic efficiency.

The atomic-level tunability that results from alloying multiple transition metals with d electrons in concentrated solid solution alloys (CSAs), including high-entropy alloys (HEAs), has produced remarkable properties for advanced energy applications, in particular, damage resistance in high-radiation environments. The key to understanding CSAs' radiation performance is quantitatively characterizing their complex local physical and chemical environments. In this study, the local structure of a FeCoNiCrPd HEA is quantitatively analyzed with X-ray total scattering and extended X-ray absorption fine

We synthesize and systematically study a series of conjugated polymers with oligo(ethylene glycol) (OEG) or alkyl chain as the side chain and poly [2,7-fluorene-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] as the polymer backbone. Replacing alkyl chain with OEG chain can decrease the π−π stacking distance of polymer backbone in thin film from 0.44 to 0.41 nm because OEG chain is more flexible than alkyl chain. As the result, the conjugated polymer with OEG side chain exhibits higher hole mobility, red-shifted absorption spectrum in thin film and smaller bandgap than those of the conjugated polymer with alkyl side chain. With the increase of the length of OEG side chain, the resulting conjugated polymers exhibit unchanged π−π stacking distance and decreased hole mobility. Moreover, owing to the large polarity of OEG chain, OEG side chain makes the conjugated polymer suitable for polymer solar cell (PSC) devices processed with polar nonhalogenated solvent, methoxybenzene. A power conversion efficiency of 4.04% is demonstrated with the resulting PSC devices. This work provides the new insight into the effect of OEG side chain on conjugated polymer, which can be used in the molecular design of novel conjugated polymer materials with excellent optoelectronic device performance. ■ INTRODUCTIONConjugated polymers have been widely used in optoelectronic devices, such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and polymer solar cells (PSCs), with the great advantages of low cost, flexibility, and solution processing. 1 For solubility of conjugated polymers, a rigid conjugated polymer backbone is always equipped with an alkyl side chain. 2 Oligo(ethylene glycol) (OEG) chain is well-known for its hydrophilicity and is always used to endow molecules/ polymers solubility in water or polar organic solvents. 3 Thus, OEG chain has been used as side chain of conjugated polymers for efficient OLED, OFET, and PSC devices processed with polar nonhalogenated solvents. 4 As optoelectronic properties of conjugated polymers are affected by the side chain, 5 the effect of OEG side chain on properties of conjugated polymers is less investigated and poorly understood. Researchers may doubt whether hydrophilic OEG side chain would disturb the π−π stacking of hydrophobic polymer backbone in conjugated polymers. This manuscript aims to provide an insight into the effect of OEG side chain on conjugated polymers.We note that OEG chain is more flexible than alkyl chain. As shown in Scheme 1, the two hydrogen atom in CH 2 unit act as steric hindrance for the rotation of CH 2 −CH 2 unit in alkyl chain, while the two lone electron pair in oxygen atom result in no steric hindrance for the rotation of O−CH 2 in OEG chain. 6 Therefore, the energy barrier of the rotation of O−CH 2 in OEG chain (E = 0.08 eV) is smaller than that of CH 2 −CH 2 in alkyl chain (E = 0.11 eV), 6 making OEG chain more flexible than alkyl chain. For conjugated polymers, alkyl side chain impedes the close π−π Scheme 1. Schematic Il...