Electron beam induced modifications in electrical properties of Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) films

Conducting polymer PEDOT:PSS [Poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate)], owing to its high electrical conductivity, enviornmental stability and low cost, is presently getting most attention for various device applications including thermoelectric, organic light emitting diodes and photovoltaics. We have investigated the irradiation effect of high energy electron beam on the electrical transport properties of PEDOT:PSS films to manifest the scope of this polymer in high radiation field and its suitability for radiation dosimeter applications. PEDOT:PSS films were deposited on flexible polyimide (Kapton) sheets using drop-cast method and irradiated up to 75 kGy dose with 1 MeV electron beam. The electrical conductivity of as deposited polymer film was similar to 3.2 S/cm which consistently falls to similar to 0.76 S/cm on irradiation dose of 75 kGy. Detailed characterization of the samples using x-ray photoelectron spectroscopy, contact angle measurement and solubility test conclusively suggested that the lowering of electrical conductivity in irradiated sample is attributed to the crosslinking of PEDOT chains and dissociation of PSS

XPS, UV–Vis, FTIR, and EXAFS Studies to Investigate the Binding Mechanism of N719 Dye onto Oxalic Acid Treated TiO2TiO_{2} and Its Implication on Photovoltaic Properties

The anchoring mechanism of N719 dye molecules on oxalic acid treated TiO2 (OA-TiO2) electrodes has been investigated using extended X-ray absorption fine structure (EXAFS) measurements, Fourier transform infrared spectroscopy (FTIR), UV−vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). The FTIR spectroscopy of OA-TiO2 electrodes revealed that the oxalic acid dissociates at the TiO2 surface and binds through bidentate chelating and/ or bidentate bridging. Analyses of EXAFS, FTIR, UV−vis, and XPS measurements of N719 dye loaded onto OA-TiO2 revealed that the binding of N719 molecules takes place via interaction between the Ru atom of the dye and O− of bidentate bridged oxalate ions at the TiO2 surface. This mechanism is quite different from the binding of N719 onto untreated TiO2 (WO-TiO2) surface, where −COOH and SCN groups of the dye directly bind to the TiO2 surface. The analyses of UV−vis data show that the amount of N719 dye loading onto OA-TiO2 surface is much higher than that onto the native TiO2 surface. In addition, the incident photon-to-current conversion efficiency (IPCE) measurements show that the presence of oxalate ions between the dye and TiO2 surface favors efficient electron transfer and therefore improvement in device efficiency. The dye-sensitized solar cells fabricated using N719 dye sensitized onto OA-TiO2 showed an efficiency of ∼4.6%, which is significantly higher than that based on a WO-TiO2 electrode (∼3.2%)

Electron beam modified zinc phthalocyanine thin films for radiation dosimeter application

Present study deals with the effect of electron beam irradiation on electrical and gas sensing properties of zinc phthalocyanine (ZnPc) thin film prepared on flexible Biaxially Oriented Polyethylene Terephthalate (BOPET) sheet. The electron beam irradiation of ZnPc films were carried out using a 10 MeV RF Linear accelerator, under different radiation dose levels from 1 kGy to 30 kGy. The pristine and irradiated films were characterized by using X-ray photoelectron spectroscopy, Atomic Force microscopy, UV-vis spectroscopy and X-ray diffraction. Samples irradiated in the dose range of 1-18 kGy exhibit linear enhancement of electrical conductance due to increasing content of adsorbed oxygen. Beyond 18 kGy the sample exhibit saturation in the content of adsorbed oxygen as well as in electrical conductance. The pristine ZnPc films exhibit excellent chemi-resistive response towards H2S gas in 1-20 ppm range at room temperature. The response of the irradiated films decreases monotonically with increasing electron beam dose due to the strong binding of oxygen at the Zn sites. A plausible mechanism of electron beam induced modification of ZnPc films and its implication on charge transport as well as chemi-resistive gas sensing behavior are discussed. This work highlight the utilization of ZnPc thin films as potential radiation dosimeter based upon linear rise in electrical conductance

Interfacial charge trapping in the polymer solar cells and its elimination by solvent annealing

The PCDTBT:PCBM solar cells were fabricated adopting a tandem layer approach to investigate the critical issues of charge trapping, radiation absorption, and efficiency in polymer solar cells. This layered structure was found to be a source of charge trapping which was identified and confirmed by impedance spectroscopy. The low efficiency in multilayered structures was related to trapping of photo-generated carriers and low carrier mobility, and thus an increased recombination. Solvent annealing of the structures in tetrahydrofuran vapors was found beneficial in homogenizing the active layer, dissolving additional interfaces, and elimination of charge traps which improved the carrier mobilities and eventually the device efficiencies