Organometallic hybrid perovskites have attracted intense attentions recently, as a new family of solution processable semiconductors for photoenergy conversion and light emission purposes. Specifically, CH3NH3PbBr3 is one type of emissive perovskites, but its quantum efficiency largely depends on the preparation procedure. Here, we use the fluorescence lifetime imaging (FLIM) technique to investigate the relation between microscopic structures and photoluminescence (PL) in CH3NH3PbBr3 polycrystalline films. By dripping poor solvents (chlorobenzene or chloroform) to accelerate the crystallization during the film preparation, we could decrease the crystal domain size from 10 μm down to 500 nm, and the corresponding PL intensity increases significantly. From the FLIM characterization of these films, we find that the PL emission is mostly from the edge of crystal domains. The PL dynamics indicates that the radiative decay of edge state is much more efficient than that of the bulk state, and the bulk state of photoexcitation undergoes an energy transfer to the edge state. This finding explains the origin of enhanced PL from CH3NH3PbBr3 films when treated with poor solvents and provides useful information for further improvement on the PL efficiency of hybrid perovskite materials.
Previously we have reported a series of perylene dimide (PDI) dimers as efficient solution-processible small molecule acceptors. In this paper we present a new solution-processible PDI trimer with triphenylamine as the romatic bridge. This trimer was synthesized by Suzuki coupling reaction and fully characterized with 1H-NMR, 13C-NMR, TOF-MS, and elementary analysis. It exhibits a broad absorption band in the wavelength range from 450 to 650 nm with a peak round 533 nm and a maximum extinction coefficient of 9.61 × 104 M-1 cm-1. Its lowest unoccupied and highest occupied molecular orbit (LUMO and HOMO) energies are −3.75 and −5.60 eV. When blend with the commercial P3HT, it gives an open-circuit voltage (Voc) of 0.73 V, a short-circuit current-density (Jsc) of 0.60 mA/cm2, a fill-factor (FF) of 51.0% and an efficiency of 0.22%. When utilizing the conjugated polymer of PBDTTT-C-T as the donor and 5% DIO as the additive, the best conventional cell yields 1.82% efficiency with a Voc of 0.99 V, a Jsc of 3.44 mA/cm2, and an FF of 53.0%.
A series of inorganic-organic photochromic ultra-thin films were fabricated by self-assembly. The photochromic properties as well as structure of the prepared ultra-thin films were discussed. It is found that the photochromic properties of the ultra-thin films were closely related to the building blocks of the films. Both the organic and the inorganic components of the self-assembled films can evidently effect the structure and photochromism properties. The optimized combination of the inorganic and organic building blocks is thus provided.
A layered superlattice, WO3-polymer/1,10-decanediamine (1,10-DAD) self-assembled multilayer film, has been fabricated by means of alternating adsorption of transition metal tungsten compound and 1,10-DAD. UV-visible spectra were employed to study the growth process. The well ordered superlattice multilayer structure of WO3-polymer/1,10-DAD SAM film was identified by small angle X-ray diffraction (SAXRD) study. The d space of the SAM film was calculated as 2.897 nm from the SAXRD data, which agrees well with the results get by thickness measurement. The SAM film showed better photochromic properties compared with those of pre-reported WO3/4,4′-Bis(aminomethyl)-Biphenyl (4,4′-BAMBP) system. It's found that the exciting improved photochromic properties of WO3-polymer/1,10-DAD films come from the polymerization of WO3 molecules in the inorganic layers. The results clearly show that the organic molecules can efficiently manipulate the microstructure of the inorganic layer as well as the photochromic properties of the self-assembled multilayer films.