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Anirban Bagui
Y7109861
Effect of electric field annealing during solvent-drying of polymer layers.
30.07.2014 (Wednesday)
4:15 pm
SCDT seminar room
Controlling the nano-morphology of organic active layers for improved organic electronic devices has recently attracted immense attention. In this thesis the changes in the polymer film properties due to thermal annealed during the solvent drying in the presence of a constant electric field across the film are studied. Comparative studies of morphological and electro-optic properties of the P3HT: PCBM based blend film and bulk hetero-structure devices have been carried out to understand the role of this electric field annealing. The external quantum efficiency (EQE) and power conversion efficiency (PCE) of the solar cells made from the electrical field annealed films were found to be significantly enhanced due to better charge transport in the films.
In order to study the effect of electric-field on the mobility of P3HT,
single carrier devices were made. The hole mobility in P3HT was found to increase monotonically with electric field strength up to 2E5 V/m. The J–V data corresponding to the space charge limited currents (SCLC) at low temperatures for P3HT based hole-only devices were fitted with the empirical model and Gaussian disorder model (GDM) for modeling the charge transport so as to interpret the findings of the XRD measurements. These confirmed an increase in crystallinity and crystallite size of the films for electric-field annealed samples.
Solar cells with the 'inverted structure' were fabricated to see if
improvement in devices performance can be achieved by electric-field annealing of their active layers. Finally, electric–field assisted treatments were carried out on some other polymer - PTB7, PCDTBT, MEHPPV - layers and the effect of the treatments on the mobility in the films were studied.
In this thesis, the application of electric fields across the active layer
of organic solar cells at the time of its formation has been shown to help achieve higher mobility polymer films for building devices that have improved performance.
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Jaidip M. Jagtap
Y8109066
Polarimetry, Optical and Fluorescence Confocal Microscopy: Study and Discrimination of Human Cervical Precancerous Tissue
2.5.2014 (Friday)
11.00 am
Biological tissue displays morphological and biochemical changes during transformation to diseased state. Optical techniques are ideal for minimally invasive detection of such changes. Light scattering has been seen to capture morphological changes, such as increase in size and density of nuclei in cells. Subtle precancerous (dysplasia) changes are probed via Mueller matrix imaging which strongly manifest in the depolarization power and retardance and are seen to differ significantly in normal and dysplastic tissues sections. Fluorescence Mueller matrix spectroscopy has been developed recently for measurements from the connective tissue regions of human cervical tissue and reveal intriguing fluorescence diattenuation and polarizance effects. The estimated fluorescence linear diattenuation and polarizance parameters were considerably reduced in the precancerous tissues as compared to the normal ones, which were also confirmed by control experiments.
Robust statistical parameters in the form of moments, specifically weighted mean, full width at half maxima, standard deviation, skewness, kurtosis and pixel counts characterizing these distributions are shown to unambiguously distinguish microscope captured images of various tissue types. Combining these parameters effectively improves the diagnosis and classifies quantitatively various classes of tissue. Optical spatial frequency spectra from different stages of human Cervical Intraepithelial Neoplasia (CIN) tissue are also evaluated as a potential quantitative pathological tool on confocal captured images. The degree of randomness of tissue structures from normal to different stages of CIN tissue can be recognized by spatial frequency analysis.
Fluctuations in the elastic light scattering spectra of normal and dysplastic human cervical tissues through wavelet transform based techniques have been analyzed and reveal clear signatures of self-similar behavior in the spectral fluctuations. The strong dependence of the elastic light scattering on the size distribution of the scatterers manifests in the angular variation of the scaling exponent. These findings using the multi-resolution analysis capability of the discrete wavelet transform can contribute to the recent surge in the exploration for non-invasive optical tools for pre-cancer detection.
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