Since the size-dependent quantum confinement effect was first observed in semiconductor crystallites synthesized in a wet-chemical method ( J. Chem. Phys. 1984 , 80 , 4464), colloidal nanocrystal quantum dots (NQDs) have become an epitome of commercially viable nanomaterials. Early on, the size-tunable optical properties and discrete energy levels in NQDs intrigued scientists from diverse disciplines into synthesis and characterization of this unique class of materials. As is the case with many

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... other nanomaterials, the optical, chemical, colloidal and electronic properties of NQDs turn out to have significant bearing on their surface structures (e.g., surface atoms-organic ligand interactions). A notable example includes the use of lead sulfide NQDs as photo-active materials in photovoltaic cells: the reported device efficiency has shown drastic surge in recently years. The epicenter of this progress is the impact of surface passivation on the performance of NQDbased photovoltaic devices. In the wake of recent development of NQDemploying commercial display devices, high emission yield and stable luminescence are called for. Studies have alluded that surface and interface of NQDs play an instrumental role in light emitting diodes. As such, it would be an understatement that the surface science is just important in the use of NQDs. Understanding what happens on the surface and interface of NQDs is of indispensable virtue. This special issue 'quantum dots for optoelectronic applications (QDOA)' in Applied Surface Science Advances is thus timely and opportune forum for the discussion on the very progressive topic. It covers from fundamental surface science to the effect of surfaces in practical optoelectronic devices, such as photovoltaic cells, light emitting diodes, and sensors of NQDs. The issue echoes the importance of surface science in NQD-based optoelectronic devices.