الفهرس 
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Abstract
Branched CdSe semiconductor nanocrystals have potential advantages in optoelectronic and photovoltaic devices, because of their shape and the charge separations within the same nanocrystal. Tetrapod is the most fundamental branched structure that results from four arranged wurtzite rods around a central cubic (zinc blende) dots. Their synthesis has been achieved by controlling the relative stability and growth of two different crystalline phases, performing the initial nucleation in zinc blende and the growth of four arms in the wurtzite phases. It has been found that switching between two crystalline phases during the growth in-situ the same nanocrystal allow branching. These branched nanocrystals have large dipole moment because there is 90.0 meV difference between the CdSe zinc blende band gab energy and its wurtzite form. New synthetic methods have been developed to achieve more control over the shape of the semiconductor nanocrystals. The factors which can affect the particle shape and the growth rate are examined systematically. Shape dependant photophyscial properties such as absorption and emission are investigated. Studying the optical and the electronic properties of these branched shapes show that these new nanomaterials are very promising as an active medium in photovoltaic devices applications. In addition, the photostability of these new particles upon irradiation using UV light has been investigated. Our results indicate that the prepared particles are not very stable upon irradiation with UV light. Their photostability depend on the particle shape and the capping material. To increase their photostability, new quantum dots (QDs) polymer composite has been fabricated which is very stable upon exposure to UV light or lasers even for days.