The dielectric responses of zinc phthalocyanine (ZnPc) thin films, deposited using the vacuum evaporation technique, were studied as functions of frequency and temperature. The conductivity of the deposited films decreases with increase in temperature. The dielectric studies clearly indicated that the Debye type of polarization exists in these films. The relaxation phenomena have been confirmed from the Cole-Cole plot. The relaxation times have been evaluated from the plot and were found to be (τa) 0.0137 and 0.0106 s at 303 and 403 K , respectively. The prevailing conduction mechanism in ZnPc films, under an ac field, was found to be electronic hopping. The activation energy was evaluated from the Arrhenius plot and was found to be 1.28 eV . Based on the structure, and with the help of quantum mechanics calculations, the electronic structure and behavior that upheld our experimental results were identified.
"The pd-hybridized and H states reveal a similar behavior. We note that our GGA DOS of free standing ZnPc shows significant improvements over previously reported results in Ref. 28, where the local density approximation has been employed, and seconds Ref. 5. The PBE0 approach yields a band gap of 1.93 eV, in excellent agreement with the experimental value29. In addition, the photoemission spectra reported in Ref. 30 are well reproduced, particularly the small feature at −0.24 eV which appears both in our GGA and PBE0 data. "
[Show abstract][Hide abstract] ABSTRACT: The adsorption geometry and electronic properties of a zinc-phthalocyanine molecule on a Cu(111) substrate are studied by density functional theory. In agreement with experiment, we find remarkable distortions of the molecule, mainly as the central Zn atom tends towards the substrate to minimize the Zn-Cu distance. As a consequence, the Zn-N chemical bonding and energy levels of the molecule are significantly modified. However, charge transfer induces metallic states on the molecule and therefore is more important for the ZnPc/Cu(111) system than the structural distortions.
[Show abstract][Hide abstract] ABSTRACT: Multilayer and 1:1 blended films of zinc phthalocyanine (ZnPc) and buckminsterfullerene (C60) were investigated as model active layers for solar cells by time-resolved terahertz spectroscopy (TRTS). Relative photon-to-carrier efficiencies were determined from ultrafast decay dynamics of photogenerated carriers using 400 and 800 nm excitation for delay times up to 0.5 ns. The findings are in good agreement with reported solar-cell device measurements, and the results exhibit a near linear increase of the relative efficiencies with the interface number of multilayer films. The relative photon-to-carrier efficiencies of films composed of alternating layers with an individual layer thickness of less than 20 nm were higher than that of a 1:1 blended film. In contrast, 400 nm excitation of a C60 only film initially yields a relatively strong THz signal that is followed by a rapid (picosecond) decay almost to its base value and results in a very low carrier density beyond a few picoseconds. For a given film thickness and optical density, our data suggest that the relative photon-to-carrier efficiency of multilayer films increases with increasing total interfacial area, emphasizing the importance of close proximity between the fullerene and phythalocyanine. These findings suggest that the highest photon-to-free-carrier efficiencies can be achieved by designing ultrathin films (having layers a few nanometers thick) with alternating multilayer structures to achieve high photon harvesting and charge separation to opposite layers.
The Journal of Physical Chemistry C 10/2009; 113(43). DOI:10.1021/jp904107x · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Sodium copper chlorophyllin (SCC) thin films were successfully prepared, using dip coating technique. Thermal gravimetric analysis (TGA) was performed for studying the thermal stability of SCC. The surface morphology of thin films was studied by using scanning electron microscopy (SEM). The crystalline structural characteristics were undertaken with the aim of determining the lattice parameters together with a complete list of the Miller indices and interplanar spacing for SCC. The molecular structure and electronic transitions of SCC were investigated by Fourier-transform infrared (FTIR) and absorption spectrum, respectively. Temperature dependence of the DC electrical conductivity, σDC was investigated in the temperature range 289–373K. Measurements revealed that the σDC behavior of the films can be described by Mott's one-dimensional variable range hopping (VRH) model in the entire temperature range. The AC conductivity, σAC(ω) results were discussed in terms of the correlated barrier hopping (CBH) mechanism for charge carrier transport. The maximum barrier height and the hopping length were estimated. The temperature dependence of the σAC(ω) shows Arrhenius type with one thermal activation energy for each frequency. The behavior of the real and imaginary parts of the dielectric constant as a function of both temperature and frequency were discussed. The energy band model was applied and the type of the optical transitions responsible for optical absorption was found to be direct allowed transition. Position dependent for SCC thin film photo-detector was studied by using laser diode source.
Journal of Alloys and Compounds 01/2011; 513. DOI:10.1016/j.jallcom.2011.10.058 · 3.00 Impact Factor
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