Hydrogen plays a critical role in the synthesis of quantum dots (QDs), particularly in applications for displays, sensors, and light-emitting diodes (LEDs). Its unique properties enable precise control over precursor reduction, size modulation, and surface passivation, which are essential for producing high-performance QDs with tailored optoelectronic characteristics.

In the context of precursor reduction, hydrogen serves as a key reducing agent in both gas-phase and solution-phase synthesis methods. During chemical vapor deposition (CVD) or metalorganic chemical vapor deposition (MOCVD), hydrogen gas is often introduced to facilitate the decomposition of metalorganic precursors. For example, in the synthesis of cadmium selenide (CdSe) QDs, hydrogen assists in breaking down dimethylcadmium (Cd(CH3)2) and hydrogen selenide (H2Se) into reactive intermediates. This controlled reduction ensures the formation of uniform nucleation sites, which is crucial for achieving monodisperse QDs. In colloidal synthesis, hydrogen-containing reducing agents such as sodium borohydride (NaBH4) or hydrazine (N2H4) are employed to convert metal salts into their elemental forms. The reduction kinetics influenced by hydrogen availability directly impact nucleation rates and, consequently, the final particle size distribution.

Size control is another critical aspect where hydrogen contributes significantly. The presence of hydrogen during synthesis affects the growth kinetics of QDs by modulating the reactivity of precursors and the stability of intermediate species. In hot-injection methods, hydrogen-containing ligands such as oleylamine or trioctylphosphine act as both reducing agents and surface stabilizers. These ligands regulate the growth rate by temporarily passivating the surface of nascent QDs, preventing uncontrolled aggregation. The balance between precursor reduction and surface stabilization determines the final size of the QDs. For instance, in indium phosphide (InP) QD synthesis, hydrogen from aminophosphine precursors not only reduces indium salts but also passivates surface defects, leading to narrow size distributions essential for color-pure emission in display technologies.

Surface passivation is vital for enhancing the photoluminescence quantum yield (PLQY) and stability of QDs. Hydrogen participates in this process by saturating dangling bonds on the QD surface, which would otherwise act as non-radiative recombination centers. In sulfide- or selenide-based QDs, hydrogen treatment post-synthesis can replace surface chalcogen vacancies with hydride groups, significantly improving optical properties. Additionally, hydrogen plays a role in ligand exchange processes where long-chain organic ligands are replaced with shorter, more conductive ones. For example, in the fabrication of QD-LEDs, hydrogen-mediated ligand exchange with thiols or halides enhances charge injection efficiency while maintaining colloidal stability.

The application of hydrogen extends to the doping and alloying of QDs, which is critical for tuning their electronic and optical properties. In the synthesis of alloyed QDs such as cadmium zinc selenide (CdZnSe), hydrogen controls the incorporation of zinc by modulating the reduction rates of cadmium and zinc precursors. This precise control enables the fine-tuning of bandgap energies, which is essential for applications in wide-color-gamut displays. Similarly, hydrogen is used in the doping of QDs with transition metals like manganese (Mn) for sensor applications. The reducing environment prevents oxidation of dopant ions, ensuring uniform distribution within the QD lattice.

In the manufacturing of QD-based displays, hydrogen’s role is evident during the encapsulation and integration stages. Residual hydrogen in the deposition environment prevents oxidation of QDs during thin-film processing, which is crucial for maintaining high PLQY in electroluminescent devices. For sensor applications, hydrogen-treated QDs exhibit improved sensitivity and selectivity due to reduced surface defects that could otherwise interfere with analyte binding. In LEDs, hydrogen-passivated QDs contribute to higher device efficiency and operational stability by minimizing non-radiative losses at the QD/charge transport layer interface.

The scalability of hydrogen-assisted QD synthesis is a key advantage for industrial adoption. Continuous-flow reactors utilizing hydrogen-based reduction enable large-scale production with consistent quality, meeting the demands of display and lighting industries. Furthermore, the compatibility of hydrogen-based processes with existing semiconductor fabrication techniques facilitates the integration of QDs into hybrid optoelectronic devices.

Despite its advantages, challenges remain in optimizing hydrogen’s role in QD synthesis. Precise control over hydrogen partial pressure, temperature, and reaction time is necessary to avoid over-reduction or unintended side reactions. Advances in in-situ monitoring techniques, such as spectroscopic ellipsometry or X-ray diffraction, are improving the reproducibility of hydrogen-mediated QD growth.

In summary, hydrogen is indispensable in the synthesis of quantum dots for displays, sensors, and LEDs. Its contributions to precursor reduction, size control, and surface passivation enable the production of high-quality QDs with tailored optoelectronic properties. As research progresses, further refinements in hydrogen-based synthesis protocols will enhance the performance and commercial viability of QD-based technologies.