**1. Introduction**

The word "'Quantum dot (QD)" is a precisely trifling structure (ranging between 1 and 10 nm wide), for instance, a semiconductor-made nanocrystal implanted in alternative semiconductor-based materials, in which the electrons or other charge carriers can be confined in all the three dimensions along with reference to the respective electronic physiognomies contingent on its shape and size. Over the past three decades, quantum dots (QDs) had well established in connection with numerous remarkable applications. Amid the supreme contemporary machineries are typically built on their attractive optical and electronic properties and their part in light absorption, emission, conversion, and detection have a massive volume of innovative day-to-day applications, and gratifying ever more controllable and accustomed to the societal nature. In 1981, Alexey I. Ekimov is a Russian solid-state physicist invented the semiconductor nanocrystals well known as quantum dots in glass matrix, while he was working at the Vavilov State Optical Institute [1]. Further, systematic progress in the remarkable science and technology of the QDs was determined in 1985, when Louis E. Burs at Columbia University come up with a relationship between size and a degree of bandgap relies on the semiconductor base nanoparticles which relates a particle of kind in a sphere model approximations to the respective wave function ideologies for the aforesaid bulk semiconductors [2–5] and the QDs were discovered from the colloidal mixture of semi-conductor nanocrystals [6]. Also, spin qubits in semiconductor quantum dots signify a prominent family of solid-state qubits, which provides greater efforts to build a quantum computer [7].

Murray et al. have efficaciously synthesized the colloidal state CdX (X = S, Se, Te) QDs along with a tunable size of band-edge absorption as well as emissions and it took more than a decade for the preparation of new-fangled QD material [4]. Owing to its outstanding optical and electrochemical physiognomies, the CdX QDs had widely investigated. In the infancy of core-shell QD research, CdSe/ZnS and CdSe/CdS are the utmost exhaustively examined materials [5, 8–10]. A decade back, increasingly new "core-shell" QDs were synthesized, such as CdSe/ZnSe [11], CdTe/ CdS [12], CdSe/ZnS, and CdTe/ZnS [13], and at even multilayer CdTe/CdS/ZnS "core/shell/shell" QDs [14]. By employing zinc stearate as a zinc source, bright luminescent and low toxic, CdSeTe@ZnS-SiO2 QDs would be made with ZnS-like clusters


#### **Table 1.**

*Reviews some major state-of-the-art development in technology connected to the applications of quantum dots in a diverse spectrum.*

*Introductory Chapter: The Fame of Quantum Dots in Space-age Improvements… DOI: http://dx.doi.org/10.5772/intechopen.108639*

packed into the SiO2 shell through a microwave-assisted process [15]. Hypersensitive type photosensors were prepared with respect to the cesium lead bromide (CsPbBr3) perovskite quantum dots (QDs) with ample amount of higher sensitivity for chemiluminescence based immunoassays [16]. Vastly luminescent all-inorganic cesium lead bromide (CsPbBr3-QDs/CuPc) heterostructures of perovskite natured quantum dots (QDs) had been comprehensively in the usage as a photosensitizer in the known optoelectronic devices, while p-type small-organic-molecule comprised of copper phthalocyanine (CuPc) would greatly use as a photoactive material in solar cells and organic field-effect transistors (OFETs) [17].

In the year 1988, Mark Reed investigated electronic transport via a three-dimensional confined semiconductor quantum well ("quantum dot"). In 2013, the first commercial deliverance of a product employing the quantum dots would be the Sony XBR X900A series of flat panel televisions. In the year 2013, the Kindle Fire HDX is released covering quantum dot technology, and a blue glow bleeding in from the edge of the display. Followed by in the year 2015, the quantum dots would be a featured innovation at the consumer electronics show, projects that, the quantum dots have been flaunted to be the next breakthrough visual technology to enhance the LED TV picture quality. In recent years, the focus is based on the development of effectual and stable lead-free wise perovskite solar cells (PSCs) and also the prospect of reaching 20% power conversion efficiency (PCE) for tin PSCs. These issues concern the enlargement of the cell size and apprehending scalable production in the future [18] (**Table 1**).
