Biosynthesis of quantum dots and their usage in solar cells: insight from the novel researches

Quantum dots (QDs) are three-dimensional (3D) quantum confinement materials with confined size on the nanoscale. They are semiconductors, possessing a tunable energy gap in the range of visible light energy. In QDs, the 3D quantum confinements of excitons result in tunable fluorescence emission relying upon the QDs size and shape when excited by monochromatic light. Besides, the attempts to improve their outstanding optoelectronic properties, i.e. superior to those of bulk, thin-film semiconductor and organic dyes, many efforts have been conducted, in recent times, regarding sustainable QDs synthesis aiming at biocompatibility and cost reduction. Among the green synthesis routes of QDs there are two distinguished; namely inorganic QDs and carbon-based QDs. The first route is made of low-bandgap metal chalcogenide either extracted from a living being, e.g. earthworm, or capped with an organic ligand. While, the second route is made of carbon-core and passivating the surface with different functional groups, namely carboxyl, hydroxyl, in addition to amine. These functional groups are derived from coke or organic carbon reservoir, i.e. fruits and their juice, animal, vegetable, spice and waste paper. Numerous fundamental applications of QDs, such as biomedicine, sensing, catalysis, and solar cells, exploit the characteristic fluorescence emission of QDs, quantum yields and their modulation upon interaction with the external environment. In this review, two prototype QDs examples are used to highlight the route to sustainable QDs synthesis and solar cells implementation and some perspectives.