اجتہاد کی شرعی حیثیت اور عصر حاضر ميں اجتہاد کی عملی صورتیں

Ijtihad is an invaluable secondary source of the Muslim jurisprudence. In Islamic law, ijtihad refers to the independent interpretation of problems not precisely covered by the sacred scripture of Islam, Qur’an, and Prophetic traditions. The savants who undertake ijtihad must be firmly rooted in knowledge and savvy what the demands of the contemporary era are. Since new challenges call for innovative solutions, the faithful cannot genuinely live by Islam without their jurists deriving the laws of sharia from its sources.

Development and Testing of Photoanode Materials for Dye Sensitized Solar Cells

This thesis describes the purposeful fabrication of TiO2 photoanode based dye sensitized solar cells (DSCs) and their detailed characterization. The aim was to investigate the structural function relationship of the photoanode on the photovoltaic performance of the devices. The hierarchical anatase TiO2 microspheres (Tmic) and nanoparticles (Tnano), with an average particle size of 0.38 µm and 20 nm, were synthesized by low cost solution and hydrothermal methods, respectively. Highly screen printable pastes of the Tmic and Tnano have been developed to prepare bifunctional films, with increased light scattering and large surface area, for the solar cells. These advantageous properties of TiO2 microspheres were evidenced by the evaluation of electrochemical and photoelectrochemical characterization. In the DSCs, these films lead to a 32% increase in conversion efficiencies when compared to those with the films of TiO2 nanoparticles only. The efficiency was further improved by TiCl4 post-treatment. In the second part of the study, the anatase TiO2 microspheres were annealed at elevated temperature of 500 oC and 900 oC for one hour in order to obtain highly crystalline and phase pure anatase and rutile TiO2 microspheres, respectively. These microspheres were used as the upper light scattering layer in a double layered structure with Tnano as the lower dye sensitization layer in anatase phase. Remarkable improvement of 48 % and 58 % in the power conversion efficiency was recorded for anatase and rutile microspherical TiO2 scattering layers respectively, in comparison to the devices having no scattering layer composition. In particular, the performance of rutile TiO2 microspheres as light scattering layer was quite high (6.3 %) due its high refractive index (2.79) than the anatase phase (2.54). Thirdly, to further improve the efficiency of the DSCs based on double layered photoanodes, the compact blocking layers were introduced beneath the absorber layer. The blocking layers of TiO2 and ZnO/TiO2 were deposited on FTO surface by electrostatic layer by layer deposition method at room temperature. These blocking layers physically blocked the access of redox electrolyte and retarded the electron back reaction at FTO/meso-TiO2/electrolyte interface.A considerable increase in electron life time (18 ms to 42 ms) was observed with these DSCs which resulted in larger short circuit current densities and higher overall power conversion efficiencies up to 9.0 %. In the fourth part of investigation, the results of differently modified pastes, using commercial TiO2 nanoparticles as the major component, have been presented. The focus iii was on the optimization of the concentration of binders and the rheological agents to develop high quality screen printed TiO2 films. The properties discussed include the porosity, cracks and aggregates, connectivity of the particles, their strong adherence to FTO surface, charge transport, and the dye uptake ability. Among the various pastes, the best paste was utilized for the screen printed photoanodes, to optimize the film thickness and the annealing temperature. The best photovoltaic performance was achieved with three layers of commercial TiO2 film of 15 µm thickness and annealed at 500oC. Finally, in the light of findings of the present research work and overall literature review, the worldly established overall certified power conversion efficiency (13%) achieved by DSCs at laboratory scale and submodule level so far in comparison to other competent solar cell technologies have been summarized.Further, the prospect of future development of DSCs to become industrially mature technology has been presented by analyzing the different challenges that needs to be carefully controlled.