الفهرس 
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Abstract
As the drive to seek alternative energy sources significantly increases across the world, there is a growing interest in low cost, easily manufactured and efficient energy sources. Among all alternative energy sources (renewable energy) such as wind, water, biomass or solar energy; the present work is focused on solar energy. A solar cell is a solid state electronic device that converts the solar energy directly into electricity by Photovoltaic (PV) effect. Ever since the French scientist Alexandre Edmund Becquerel discovered the PV effect in 1839, the research in the field of solar cells is continuously progressing and now is the era of third generation solar cells. Quantum Dot Sensitized Solar Cells (QDSSCs) and Organic Solar cells (OSCs) emerged out to be a potential candidate in converting solar energy directly into electricity.The Quantum Dots (QDs) layer also plays very an important role in performance of QDSSCs and OSCs. The unique properties of (II-VI) semiconductor materials such as direct bandgap, tunable size and hence bandgap, broad absorption spectrum, narrow emission spectrum, high temperature stability and large extinction coefficient make them attractive for solar cell applications. QDSSCs are a promising low cost alternative to existing PV technologies such as crystalline silicon (Si) and thin inorganic films. A QDSSC make use of (QDs) as light absorbing material. The absorption spectrum of QDs can be tailored by controlling their size. So, different sized QDs of varying wavelengths having absorption maximum peaks in the entire visible spectrum can be used in QDSSCs to harness solar energy efficiently. QDSSC is composed of four main components: (1) a 2-20 μm thick, porous, wide bandgap semiconductor film (typically TiO2) composed of crystalline nanoparticles abutting one another coated on transparent conducting oxide (TCO) glass (2) QDs adsorbed onto these nanoparticles (3) a hole conductor electrolyte interpenetrating the nanocrystalline semiconductor network and (4) a counter electrode (CEs).An OSCs or plastic solar cell are another promising and its a type of photovoltaic that uses organic electronics, a branch of electronics that deals with conductive organic polymers or small organic molecules blended with QDs, for light absorption and charge transport to produce electricity from sunlight by the photovoltaic effect. Most organic photovoltaic cells are polymer solar cells.