**7. Application of group IIB-VIA semiconductor QDs**

Most essential part of these QDs is their application in optoelectronics such as light emitting diodes [91–99], photodetectors [100] and photovoltaic solar cells or quantum dot sensitized solar cells (QDSSC) [101–105]. Colvin and his associates had first designed QD-LED (1994) [91] and this invention was a milestone in optoelectronics. The quantum efficiency of first CdSe QDs was 0.01%, which was a better result in that time, although much lesser than today's QD-LEDs. The reason behind fast development of efficiency of the QDs in LEDs is the report of newer developments in synthesis methodologies and their quality along with that. Recently, impressive development has been made by Samsung electronics in the form of quantum dot televisions. The manufacturing authority claims that the color intensity is much more intense than an ordinary TV and it happens due to the incorporation of QDs. The greatest potential of colloidal QDs in optoelectronics lies in their humongous flexibility of semiconducting and optical nature over wide range of light spectrum, which allows the tailoring of QDs according to their desired applications. In addition to that, the low cost production and effective charge transfer capability also offers these dots the suitability in optoelectronic appliances. The utility of the QDs in LEDs or QDSSCs can be consolidated by fabricating the thin films of them. Thin films are the easiest but effective support as well as cost effective solution to incorporate the highly luminescent QDs in a device. In thin film science, a thickness range of nanometers to a few micrometers of the synthesized QDs is spread over suitable templates (commonly used glass, ITO, FTO, mica, etc.) by various methods (e.g., chemical vapor deposition, electron beam deposition, spin coating, dipping, etc.). First generation silicon solar cells were the first thin film solar cells, however, slowly 3rd generation thin film solar cell has been replacing them. In the preparation of a thin film, the suitable roughness according to their thickness has to be maintained to receive desired optical luminescence. In the fabrication of thin films, the methodology to prepare them is very important. It is because during the process of fabrication, the characteristics of the synthesized QDs must not change, as making of thin films may undergo different rigorous

*Aqueous-Mediated Synthesis of Group IIB-VIA Semiconductor Quantum Dots: Challenges… DOI: http://dx.doi.org/10.5772/intechopen.82891*

treatment including heating too. Therefore, to find a valid and effective method of thin film fabrication is very important. Simultaneously, the cost of production of the thin films also has to be minimal so that the product will be a cheaper one. Hence, research is undergoing intense investigation to find a low cost and effective way of production of QD thin films, which can necessarily, fulfill the demand of industry as well as global market. Although having tremendous potential utility of these QDs in various application fields of science and technology, their high production cost (~\$10,000 per gram of QDs) makes it difficult to raise them as a part of our day to day life [106, 107]. Unless scientists develop some sort of easier and cost effective way to produce and fabricate specific shape and sized QDs in mass scale, we cannot understand their broad application [108]. Therefore, chemical engineering of QDs has begun to solve these two major following issues: (a) use of eco-friendly inexpensive starting material for synthesis of QDs and (b) development of green synthesis routes with the optimization of all the reaction parameters [62]. Therefore, it is become mandatory for the research community to design newer and greener optimized synthesis processes, so that in near future these QDs can become leader in every aspects of mankind.
