Shuaifeng Hu

Abstract:

The toxicity of lead perovskite hampers the commercialization of perovskite-based photovoltaics. While tin perovskite is a promising alternative, the facile oxidation of tin(II) to tin(IV) causes a high density of defects, resulting in lower solar cell efficiencies. Here, we show that tin(0) nanoparticles in the precursor solution can scavenge tin(IV) impurities, and demonstrate that this treatment leads to effectively tin(IV)-free perovskite films with strong photoluminescence and prolonged decay lifetimes. These nanoparticles are generated by the selective reaction of a dihydropyrazine derivative with the tin(II) fluoride additive already present in the precursor solution. Using this nanoparticle treatment, the power conversion efficiency of tin-based solar cells reaches 11.5%, with an open-circuit voltage of 0.76 V. Our nanoparticle treatment is a simple and broadly effective method that improves the purity and electrical performance of tin perovskite films.

Abstract:

Endohedral metallofullerenes (EMFs), namely fullerenes with metallic species encapsulated inside, represent an ideal platform to investigate metal-metal or metal-carbon interactions at the sub-nanometer scale by means of single-crystal X-ray diffraction (XRD) crystallography. Herein, recent progress in the identification of new structures and unprecedented properties are discussed according to the categories of monometallofullerenes, dimetallofullerenes, carbide clusterfullerenes, and nitride clusterfullerenes. In particular, the dimerization and the cage-isomer dependent oxidation state of the inner metal atom are summarized in terms of pristine monometallofullerenes. Metal-metal bonds involving lanthanide-lanthanides or actinide-actinides are discussed based on both experimental and theoretical studies. The cluster-cage matching and/or mutual selections, as well as the rarely seen M=C double bonds, are discovered in M₂ C₂ @C_2n , U₂ C@C₈₀ , M₂ TiC@C₈₀ , and Ti₃ C₃ @C₈₀ . Subsequently, the geometries of different M₃ N clusters in various cages are discussed, revealing size-matching between the internal M₃ N cluster and the outer cage induced by the planarity of the cluster. Finally, an outlook regarding the future developments of the molecular structures and applications of EMFs is presented.

Abstract:

Six dierbium carbide endohedral metallofullerenes have been synthesized and chromatographically isolated. Single-crystal X-ray diffractometry unambiguously ascertains their structures as Er₂C₂@C_2v(5)-C₈₀, Er₂C₂@C_s(6)-C₈₂, Er₂C₂@C_s(15)-C₈₄, Er₂C₂@C_2v(9)-C₈₆, Er₂C₂@C_s(15)-C₈₆, and Er₂C₂@C_s(32)-C₈₈, respectively. The Er···Er distances of the major erbium sites inside the C_s(6)-C₈₂, C_2v(5)-C₈₀, C_s(15)-C₈₄, C_s(15)-C₈₆, C_2v(9)-C₈₆, and C_s(32)-C₈₈ cages are 3.801, 3.860, 4.062, 4.066, 4.307, and 4.372 Å, respectively, which show a linear tendency with an increase in the major axis of the fullerene cages (8.064, 8.238, 8.508, 8.582, 8.815, and 8.953 Å, respectively). Furthermore, the electrochemical and molecular orbital analyses reveal that the redox chemistry of the Er₂C₂@C_80-88 isomers is associated with the carbon cage, which is different from the situations found for typical dimetallofullerenes, such as Y₂@C₈₂, Er₂@C_82-84, and Lu₂@C_82,86 isomers, which show metal-dependent oxidation processes, indicating the importance of C₂ insertion in carbide cluster metallofullerenes.