Colloidal quantum dots (CQDs) have attracted tremendous research interests in future-generation energy, electronic, optoelectronic, and bio-imaging applications due to their fascinating material properties, such as solution processability at room temperature and under ambient conditions, compatibility with various functional materials, and high photostability as well as photosensitivity. Among the various optoelectronic applications of CQDs, optical light sensors, which convert photonic energy into electrical signals, have been of particular interest because they are one of the key building blocks for modern communication and imaging applications, including medical X-ray and near-infrared imaging, visible light cameras, and machine vision. However, CQDs, which have been widely researched for photodetectors (PDs) so far, contain toxic and hazardous heavy metals, namely, lead (Pb), cadmium (Cd), and mercury (Hg). These substances are extremely toxic and harmful to the environment as well as human beings. Therefore, it is highly desirable to substitute CQDs containing heavy metals with nontoxic and environmentally friendly ones to realize green optoelectronics. In this review article, we introduce various kinds of heavy metal–free CQDs and their PD applications. This article comprehensively includes working mechanisms of PDs, various kinds of nontoxic and environmentally friendly CQD-based PDs, advanced heterojunction PDs, and discussion for future perspectives.
Wavefunction engineering: From quantum wells to near-infrared type-II colloidal quantum dots synthesized by layer-by-layer colloidal epitaxy
