Efficient Perovskite Solar Cells Based on Tin Oxide Nanocrystals with Difunctional Modification.

Tin oxide (SnO2 ) nanocrystals-based electron transport layer (ETL) has been widely used in perovskite solar cells due to its high charge mobility and suitable energy band alignment with perovskite, but the high surface trap density of SnO2 nanocrystals harms the electron transfer and collection within device. Here, an effective method to achieve a low trap density and high electron mobility ETL based on SnO2 nanocrystals by devising a difunctional additive of potassium trifluoroacetate (KTFA) is proposed. KTFA is added to the SnO2 nanocrystals solution, in which trifluoroacetate ions could effectively passivate the oxygen vacancies (OV ) in SnO2 nanocrystals through binding of TFA- and Sn4+ , thus reducing the traps of SnO2 nanocrystals to boost the electrons collection in the solar cell. Furthermore, the conduction band of SnO2 nanocrystals is shifted up by surface modification to close to that of perovskite, which facilitates electrons transfer because of the decreased energy barrier between ETL and perovskite layer. Benefiting from the decreased trap density and energy barrier, the perovskite solar cells exhibit a power conversion efficiency of 21.73% with negligible hysteresis.

Multiple-Function Surface Engineering of SnO2 Nanoparticles to Achieve Efficient Perovskite Solar Cells.

The mismatched energy-level alignment and interface defects of the SnO2 nanoparticles' electron transport layer (ETL) and perovskite layer worsen the efficiency of the perovskite solar cell. Herein, we devise a multiple-function surface engineering of SnO2 nanoparticles. TBA+ ions improve the dispersion and stability of colloidal T-SnO2 nanoparticles and act as a bridge between the ETL and perovskite layer through the electrostatic interaction with anions, thus suppressing the charge recombination and reducing the energy loss. I- ions passivate oxygen vacancies of SnO2 nanoparticles but also halide vacancies of the perovskite layer. Furthermore, the conduction band edge of T-SnO2 is enhanced to match the energy alignment with the perovskite, which reduces the energy offset for electron transfer. As a result, the champion solar cell based on T-SnO2 presented a power conversion efficiency of 21.71% with a VOC of 1.15 V and negligible hysteresis, which are much higher than those of the reference device.

Spray Coated Colloidal Quantum Dot Films for Broadband Photodetectors.

A technique for scalable spray coating of colloidal CdSeTe quantum dots (QDs) for photovoltaics and photodetector applications is presented. A mixture solvent with water and ethanol was introduced to enhance the adhesive force between QDs and the substrate interface. The performance of the detector reached the highest values with 40 spray coating cycles of QD deposition. The photodetectors without bias voltage showed broadband response in the wavelength range of 300-800 nm, and high responsivity of 15 mA/W, detectivity of more than 1011 Jones and rise time of 0.04 s. A large size QD-logo pattern film (10 × 10 cm2) prepared by the spray coating process displayed excellent uniformity of thickness and absorbance. The large area detectors (the active area 1 cm2) showed almost the same performance as the typical laboratory-size ones (the active area 0.1 cm2). Our study demonstrates that the spray coating is a very promising film fabrication technology for the industrial-scale production of optoelectronic devices.

Fluorinated graphene as an anticancer nanocarrier: an experimental and DFT study.

The unique physicochemical properties and structure of fluorinated graphene (FG) hold great promise in biological fields, however, the strong hydrophobicity and chemical inertness heavily limit its further application, and the mechanism or utilization of FG as a drug nanocarrier has been rarely studied. Herein, a conceptual application of FG for loading doxorubicin (DOX) and cancer chemo-photothermal therapy is reported, and the interaction between FG and DOX was systematically investigated by density functional theory (DFT). To accomplish this, a mild method to synthesize stable and well-dispersed fluorinated graphene oxide (FGO) was developed, which exhibited excellent photothermal performance in the near infrared region (NIR), a high drug loading capacity (more than 200%), pH-triggered drug release, low cytotoxicity and good combination therapy effects. DFT results demonstrated that the introduction of fluorine provided more active sites for intermolecular interactions between DOX and FGO, and non-covalent interactions were the driving forces for drug loading and release. The presented method to employ FGO as an effective nanocarrier and the study of its interaction with drugs greatly broaden the further applications of FG, and provide new insights into developing novel drug delivery systems.

DFT study on the dissolution mechanisms of α-cyclodextrin and chitobiose in ionic liquid.

Density functional theory (DFT) was employed to study the dissolution mechanisms of α-cyclodextrin and chitobiose in 1-ethyl-3-methyl-imidazolium acetate ([Emim][OAc]). Geometrical analysis of the studied complexes indicated that both anion and cation in ionic liquid interacting withα-cyclodextrin and chitobiose contributed to the dissolution reaction. Intermolecular interactions in the complexes were identified as non-covalent interactions, such as hydrogen bonds, van der Waals interactions and repulsions, which were considered as the driving force of dissolution. Among them, hydrogen bonding interactions played a dominant role, which was further visualized in the real space by combination of atoms in molecules (AIM) and reduced density gradient (RDG) techniques. The nature of intermolecular orbital interactions was characterized using natural bond orbital (NBO) theory.

Theoretical study on the alkylation of o-xylene with styrene in AlCl3-ionic liquid catalytic system.

To explore sustainable catalysts with innovative mechanisms, the alkylation mechanism of o-xylene with styrene was studied using DFT method in AlCl3-ionic liquid catalytic system. The reaction pathway was consisted of CC coupling and a hydrogen shift, in which two transition states were found and further discussed. The reactive energy catalyzed by superelectrophilic AlCl2+ (12.6kcal/mol) was distinctly lower than AlCl3 (43.0kcal/mol), which was determined as the rate-determining step. Mulliken charge along IRC gave a comprehensive understanding of charge distribution and electron transfer in dynamic progress. Bond orders and AIM theory were used to study the nature of chemical bonds and the driving forces in different reaction stages.

Fluorinated carbon fiber as a novel nanocarrier for cancer chemo-photothermal therapy.

Although biomedical applications of carbon materials such as fullerenes, carbon nanotubes and graphene have been intensively studied in recent years owing to their unique chemical and physical properties, fluorinated carbon fiber (FC) has been rarely explored in biomedicine, mostly because of it's large-size, needle-like structure and strong hydrophobicity. In this study, for the first time we developed a novel FC-based nano-carrier with good biocompatibility, high drug-loading capacity and enhanced photo-thermal performance. A simple and feasible strategy is first employed to transform commercial FC into nano-sized ones with good solubility in both water and culture medium. The changes in surface wettability then facilitated us to load doxorubicin (DOX) onto the FC viaπ-π stacking interactions. Successful regulation of structure and composition also endows FC with an enhanced photothermal response in the near-infrared (NIR) region. Moreover, cell experiments indicate that the constructed nanocarrier can be easily transferred into cells by endocytosis, showing low toxicity and exhibiting excellent cancer therapy effects resulting from a good combination of chemotherapy and photothermal therapy. Considering the low cost, high synthesis efficiency and outstanding properties of FC, the newly developed nanocarrier may find widespread applications in biomedicine and other related fields.

Cellobiose as a model system to reveal cellulose dissolution mechanism in acetate-based ionic liquids: Density functional theory study substantiated by NMR spectra.

Cellulose dissolution mechanism in acetate-based ionic liquids was systematically studied in Nuclear Magnetic Resonance (NMR) spectra and Density Functional Theory (DFT) methods by using cellobiose and 1-butyl-3-methylimidazolium acetate (BmimAc) as a model system. The solubility of cellulose in ionic liquid increased with temperature increase in the range of 90-140°C. NMR spectra suggested OAc(-) preferred to form stronger hydrogen bonds with hydrogen of hydroxyl in cellulose. Electrostatic potential method was employed to predict the most possible reaction sites and locate the most stable configuration. Atoms in molecules (AIM) theory was used to study the features of bonds at bond critical points and the variations of bond types. Simultaneously, noncovalent interactions were characterized and visualized by employing reduced density gradient analysis combined with Visual Molecular Dynamics (VMD) program. Natural bond orbital (NBO) theory was applied to study the noncovalent nature and characterize the orbital interactions between cellobiose and Bmim[OAc].