Abstract: Colloidal quantum dots (CQDs) are promising semiconducting materials, which can be used as a photoactive layer in various optoelectronic applications, because of their size-tunable bandgap energy, solution processability, and excellent optical and optoelectronic properties. In particular, these features have generated great interest in the development of CQD solar cells and led to a rapid increase in their power conversion efficiency. These improvements were enabled by many innovative approaches in terms of CQD's surface chemistry and device architecture optimizations. In this review, a critical overview of the research progress in CQD solar cells is presented with a focus on the strategies adopted for achieving record efficiency in CQD solar cells. These strategies include the use of organic/inorganic surface ligands, pre- and post-treatment of CQDs, and solid-state/solution-phase ligand exchange. Additionally, we provide an understanding of the research history to inspire the rational design of next-generation CQD optoelectronic devices, such as solar cells, light-emitting diodes, and photodetectors. Recent research on the development of infrared CQD solar cells as complementary platforms to other solar cell technologies is also critically discussed to provide another perspective on CQD technologies.

Key words: Quantum dot, Lead sulfide, Ligand exchange, Colloidal ink, Infrared light, Solar cell