Xinyan Zhao

FRET-based probe for fluoride based on a phosphorescent iridium(III) complex containing triarylboron groups

An excellent F−probe (complex 1) based on carbazole-fluorene-carbazole (CzFCz) as a fluorescent donor and a cationic Ir(III) complex unit containing dimesitylboryl (Mes2B) groups as a phosphorescent acceptor has been designed and synthesized. Several reference compounds, such as complex 2 which is similar to complex 1 but without Mes2B groups, fluorescent donor CzFCz, and phosphorescent acceptors A1 and A2, were also synthesized in order to better understand the influence of Mes2B groups on the excited state properties and fluorescence resonance energy transfer (FRET) in this system. The introduction of Mes2B groups on the ligands of the Ir(III) complex unit can lead to a red-shifted and more intense absorption, facilitating efficient FRET from the fluorescent donor to the phosphorescent acceptor. Complex 1 displayed highly efficient orange-red phosphorescent emission with an emission peak at 584 nm in CH2Cl2 solution at room temperature. The emission wavelength of complex 1 in film is red-shifted to 600 nm with a shoulder at 650 nm, and its quantum efficiency in film was measured to be 0.15 under excitation at 450 nm. Utilizing the specific Lewis acid–base interactions between boron atom and F−, the binding of F− to complex 1 can change its excited state and suppress FRET, quenching the phosphorescent emission from the Ir(III) complex and enhancing the fluorescent emission from CzFCz. Thus, a visual change in the emission color from orange-red to blue was observed. Optical responses of complex 1 to F− revealed that it can be used as a highly selective, colorimetric and ratiometric optical probe for F− utilizing the switchable phosphorescence and fluorescence.

Optically-controlled high-speed terahertz wave modulator based on nonlinear photonic crystals.

An optically-controlled terahertz (THz) modulator based on nonlinear photonic crystals (PCs) is proposed, which has the merits of high speed, compactness and easy integration. The PC structure consists of point and line defects. High speed modulation of THz wave can be realized by filling one of the point defects with organic polymer polyaniline which has rapid nonlinear response time. Simulation results show that the modulation rate, modulation depth and insertion loss of the modulator achieve 2.5 GHz, 20.3 dB and 1.02 dB, respectively.

Electrospray Dense Suspensions of TiO2 Nanoparticles for Dye Sensitized Solar Cells

We report the feasibility of using electrospray to atomize dense suspension of nanoparticles with high solid concentrations. We demonstrate this principle through electrospraying dense suspensions of TiO2 nanoparticles with 40 wt.% in ethylene glycol. A dye sensitized solar cell (DSSC) is fabricated by electrospray deposition and the power conversion efficiency up to 6.81% is demonstrated. This simple, one-step process can fabricate the active layer with uniform thickness and multiple length scales, including 25 nm TiO2 nanoparticles, ∼2 μm micro spherical particles, and ∼20-μm-thick film. A judicious choice of drying temperature is important to ensure complete drying of suspension droplets while avoiding creation of hollow particles, because the hollow particles exhibit significantly lower carrier mobility and short circuit current. The very high solid concentration demonstrated in this work can potentially reduce the manufacturing cost of DSSC because less energy will be wasted on evaporating and/or recycling the organic solvent. In addition, because electrospray is compatible with roll-to-roll process and the yield is scalable through multiplexed electrosprays, the electrospray route is a promising and economically competitive approach for manufacturing DSSCs through spray deposition. Copyright 2013 American Association for Aerosol Research

Structure optimization of organic planar heterojunction solar cells

The management of light absorption in organic photovoltaic cells is of great importance for exciton generation and thus photocurrent. Sufficient light harvesting can be established by localizing the maxima of light absorption density in the region of active layer. Using organic photovoltaic (OPV) devices based on copper phthalocyanine (CuPc) and bulkfullerene (C60) as an example, we demonstrate the methods for localizing the optical interference peaks of the main absorbed light wavelengths inside the respective active layers. The fundamental regulations of the electromagnetic field distribution with thicknesses of the active layers are clarified. The influence of the thickness of the cathode buffer layer on the optimized active layer thicknesses is discussed. Exciton diffusion modelling is combined with optical modelling to give theoretically optimized device structures. The consistency between the results of simulation and experiments is shown, which indicates the validation of the guidance of the modelling work presented in this paper for the design of effective light-using OPV devices.

A thermal stable cathode buffer based on an inexpensive tetranuclear zinc(II) complex for organic photovoltaic devices

An inexpensive material, i.e., tetranuclear zinc(II) complex, (Zn4O(AID)6) [AID = 7-azaindolate], was utilized as a cathode buffer in organic photovoltaic (OPV) devices, leading to the improvement of device performance. Compared to OPV devices based on a conventional cathode buffer of TPBi (1,3,5-tris(2-N-phenylbenzimidazolyl)benzene), although the freshly prepared devices showed similar performance, when heated to a series of high temperatures under air, the short circuit current and the open circuit voltage of the Zn4O(AID)6 devices dropped more slowly, indicating the superiority of using Zn4O(AID)6 as a cathode buffer over TPBi in OPV devices.