Quantum dots, also known as nanocrystals, are a special class of materials known as semiconductors, which are crystals composed of periodic groups of II-VI, III-V, or IV-VI materials. Their size ranges from 2-10 nanaometers. At these small sizes materials behave differently, giving quantum dots unprecedented tunability and enabling never before seen applications to science and technology. They have properties that are between those of bulk semiconductors and those of discrete molecules. They are prepared by chemical methods and are very simple and economic. Quantum dots offer the unnatural ability to tune the band gap. Changing the geometry of the surface of the quantum dot also changes the band gap energy. The band gap in a quantum dot will always be energetically larger. Quantum dots are particularly significant for optical applications due to their theoretically high quantum yield. QDs can be solution processed and could be an alternative to commonly employed sensitizer molecules. QDs allow energy level matching between desired donor and acceptor materials which is crucial in designing efficient photovoltaic devices. Quantum dots offer the possibility of boosting the energy conversion efficiency of the solar cell because of their smaller size. QDs can be used in light emitting diodes. They have applications in photonics and telecommunications. Inks and paints for security and anti-counterfeiting applications that can be applied to any surface, including paper, plastic or metal have formulated using quantum dots. Quantum dot technology is one of the most promising candidates for use in solid-state quantum computation.
Various synthesis methods have been reported for the preparation of quantum dots with different size and shapes. One of the most efficient methods of preparation of QDs is the Colloidal synthesis. Monodisperse, high quality, single-crystal PbSe nano rods were synthesized in a catalyst free, one-pot reaction using a phosphene selenide precursor. High quality InP and InAs have been synthesized by rapid mixing and heating of group III and V precursors in high boiling coordinating solvent. Colloidal nanocrystal heterostructures were prepared by seed growth method. The prepared samples were extensively characterized with the aid of several techniques.
The main objective of the present work is to synthesis Quantum dots of dumb bell shaped PbSe/PbTe system especially by colloidal method. During the first phase of the synthesis, nanorods of PbSe can be synthesized. Then introduce PbTe nano particles into the active ends of PbSe nanaorods in order to form a dumb bell shaped PbSe/PbTe system. The synthesized QDs can be characterized by various techniques such as XRD, TEM, SEM, PCS, etc. These quantum dots are employed in QDSCs to improve its efficiency. Attempts are there to tune the band gap of quantum dots by varying its size.