The Influence Of Monomer Molar Ratio On The Growth Of PbSe Nanoparticles

PbSe nanoparticles are typical narrow band gap semiconductor nanomaterials. Among the many semiconductor nanocrystal materials under investigation for photovoltaic applications, PbSe nanocrystals have been recognized as one of the most intriguing candidates. Synthetic control over the nanoparticles diameter combined with the large exciton Bohr radius of PbSe (46 nm) permits precise tuning of the quantum confined energy gap in the range of 0.3-1.0 eV-enabling solar energy conversion in the near-infrared. It is also widely used in solar cells, near-infrared detectors. Peng et al reported the growth mechanism of CdSe nanocrystals and the influence of ligands and monomer molar ratio on the growth of CdSe nanocrystals. The study showed that the molar ratio of monomer and the ligands have significant impact on the crystal growth and crystal morphology. Subsequently, many people reported influence of ligands on PbSe nanocrystals growth, such as acetic acid. The present paper discusses the influence of monomer mole ratio on the nucleation and growth of PbSe nanocrystals.In this paper, we study the influence of monomer molar ratio (Se:Pb = 1:3, 2:1, 5:1, 10:1) on the nucleation and growth of PbSe nanoparticles. The result showed that when the monomer molar ratio less than 1, the nucleation more difficult at crystal nucleation stage. At crystal growth stage, the general trend was that the growth of PbSe nanoparticles slowed as the monomer molar ratio increased. This may be the role of ligands since there are more and more study emphasize that the the ligands have significant impact on the crystal growth and crystal morphology. As the ligands concentration in the experiment remained the same and the growth of PbSe nanoparticles in the crystal growth stages were slowed with the molar ratio increased orderly. The impact of ligands cannot affect the growth of PbSe nanoparticles significantly in the nucleation and growth stage.Base on classic crystallization theory, the only possible reason is the different monomer molar ratio influence the solution activity. The experimental data showed that when the monomer molar ratio is greater than 1, the nucleation easier. It indicates that the selenium monomer is more active than the lead monomer. As a result, the more selenium monomer existed in the initial stage, the degree of supersaturation was higher, so that the driving force was lager, the faster the nucleation process occurred, and the more nuclei were generated in the nucleation stage. Consequently, the remaining monomer concentration product right after the nucleation stage in the solution decreased significantly, the degree of supersaturation lower at the time, the driving force was smaller, which resulted in PbSe nanoparticles with a slowed growth.