Technological progress in optoelectronic field is being driven by an ever-increasing demand for functional materials. Quantum dots (QDs) are one of choices, which can offer superior optoelectronic properties benefitting from quantum confinement effect. The quantum confinement is attributed to nanoscale sizes comparable to or smaller than the de Broglie wavelength of the electron wave function. To date, cadmium-based chalcogenide quantum dots have been extensively studied, whose further commercialization, however, has been hindered mainly by cost issue associated with complex and expensive fabrication processes to form core/shell structures in order to improve the material stability. Lead halide perovskite quantum dots (PeQDs) with high brightness, high color purity, and a lower cost than the conventional cadmium-based chalcogenide QDs have been considered as alternatives for the applications in optoelectronics. In this chapter, a comprehensive account of the research carried out so far is presented and the focus is on the materials aspects of conventional III–V, II–VI semiconductor nanocrystals, and recently emerging PeQDs in terms of materials syntheses, materials characterization, and applications. It is worth mentioning that most of the methods reported for the synthesis of PeQDs pose a significant threat to the environment due to the use of volatile-organic and toxic solvents, such as octadecene (ODE), dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO). A novel green-route synthesis approach is presented herein. A series of characterization techniques are presented, which is of critical significance for the study of the properties and defects and the quality improvements of the materials. Finally, solar cells as a promising application for QD-based materials are presented, and the challenges and some possible solutions to improve the stability and performance of solar cells are provided.