Design and development of organic photovoltaics based on π-conjugated materials

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The whole thesis has been organized into six chapters. The first chapter is about the brief introduction of Organic Photovoltaic devices and some recent developments in the Dye sensitized solar cells (DSSC), basic working principle of dye sensitized solar cell (DSSC), a detail explanation of components including in device. This chapter is concluded with the current state-of–the-art scenario and challenges related to design and synthesis of various wide band gap D-π-A, D-A- π-A dyes with a brief literature survey, including performance parameters and stability. The second chapter includes the design and synthesis of four new series of organic dyes based on meta-fluorine substituted phenyl moiety, used as a π-linker in various dyes, used for dye sensitized solar cell (DSSC) application. Without addition of any co-absorbent on TiO2 layer we achieved highest efficiency (PCE) of 4.4% by using a simple m-Cz-dye due to the deep HOMO level, high molar absorption coefficient (13,126 M-1Cm-1), planarity of backbone and long excitation life time value (ns) = 1.25. The third chapter demonstrates the effect of various TiO2 thicknesses with new series of dyes having ortho-fluorine substituted phenyl spacers contain different donors like carbazole, triphenylamine and phenothiazine moieties. The Optical, electrochemical, molecular orbital calculation and photovoltaic properties for different TiO2 thicknesses (9-12μm) of the new dyes were investigated. Thicknesses of TiO2 film have effects on open circuit voltage (Voc), short circuit current (Jsc) and efficiency. We observed that the Jsc and Voc of o-Cz dye with a TiO2 film thickness of 12 μm (8.91 mA/cm2 and 0.63 V) are larger than film thickness of 9 μm (8.40 mA/cm2 and 0.57 V). It could be due to the increase in thickness of TiO2 film. At optimum thickness of TiO2 film (12 μm), o-Cz dye exhibits power conversion efficiency () of 3.63( 0.4)%. This was improved efficiency of o-Cz dye from 3.3% to 4.0% without using any coabsorbents, while changing the thickness of TiO2 film. The fourth chapter explains about the synthesis of new AIEE based materials and its application in DSSC. Two chromophores TPAPHA, TPA-PFA exhibits AIEE property due to the formation of excimer in aggregation state
SUPERVISOR: Parameswar K. Iyer