Considering the environment protection, “green” materials are increasingly explored for photovoltaics. Here, we developed a kind of quantum dots solar cell based on nitrogen-doped carbon dots. The nitrogen-doped carbon dots were prepared by direct pyrolysis of citric acid and ammonia. The nitrogen-doped carbon dots’ excitonic absorption depends on the N-doping content in the carbon dots. The N-doping can be readily modified by the mass ratio of reactants. The constructed “green” nitrogen-doped carbon dots solar cell achieves the best power conversion efficiency of 0.79 % under AM 1.5 G one full sun illumination, which is the highest efficiency for carbon dot-based solar cells.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1231-1) contains supplementary material, which is available to authorized users.

Organic cathode materials as economical and environment‐friendly alternatives to inorganic cathode materials have attracted comprehensive attention in potassium‐ion batteries (KIBs). Nonetheless, active material dissolution and mismatched electrolytes result in insufficient cycle life that definitely hinders their practical applications. Here, a significantly improved cycle life of 1000 cycles (80% capacity retention) on a practically insoluble organic cathode material, anthraquinone‐1,5‐disulfonic acid sodium salt, is realized, in KIBs through a solid‐electrolyte interphase (SEI) regulation strategy by ether‐based electrolytes. Such an excellent performance is attributed to the robust SEI film and fast reaction kinetics. More importantly, the ether‐electrolyte‐derived SEI film has a protective inorganic‐rich inner layer arising from the prior decomposition of potassium salts to solvents, as revealed by X‐ray photoelectron spectroscopy analysis and computational studies on molecular orbital energy levels. The findings shed light on the critical roles of electrolytes and the corresponding SEI films in enhancing performance of organic cathodes in KIBs.

p-Benzoquinone (BQ) is a promising cathode material for lithium-ion batteries (LIBs) due to its high theoretical specific capacity and voltage. However, it suffers from a serious dissolution problem in organic electrolytes, leading to poor electrochemical performance. Herein, two BQ-derived molecules with a near-plane structure and relative large skeleton: 1,4-bis(p-benzoquinonyl)benzene (BBQB) and 1,3,5-tris(p-benzoquinonyl)benzene (TBQB) are designed and synthesized. They show greatly decreased solubility as a result of strong intermolecular interactions. As cathode materials for LIBs, they exhibit high carbonyl utilizations of 100% with high initial capacities of 367 and 397 mAh g −1 , respectively. Especially, BBQB with better planarity presents remarkably improved cyclability, retaining a high capacity of 306 mAh g −1 after 100 cycles. The cycling stability of BBQB surpasses all reported BQ-derived small molecules and most polymers. This work provides a new molecular structure design strategy to suppress the dissolution of organic electrode materials for achieving high performance rechargeable batteries.

Molecular structure and electrode architecture play very important roles in electrochemical performance of polymer electrode materials for lithium-ion batteries. Here, a series of anthraquinone-containing polymers with linear (with different molecular weights (MWs)) or cross-linked polymer structures were synthesized by (living) ring-opening metatheses (co)­polymerization method. The influences of the molecular structures and electrode preparation process on the architectures and electrochemical performance of polymer electrodes were systematically investigated. It was found that the low MW linear polymers suffer from severe dissolution and thus result in low initial capacity and poor cycling stability. Under optimized electrode preparation process, high MW linear polymers can be uniformly composited with conductive additives and binders and deliver stable cycling performance. Cross-linked polymer shows significantly reduced solubility but a severe aggregation problem, leading to very poor electrochemical performance. Our findings shed light on the molecular structure design and electrode preparation process of polymer electrode materials for high-performance rechargeable batteries.

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