Semiconductor nanocrystals and methods of preparation
A method for preparing semiconductor nanocrystals is disclosed. The method comprises adding a precursor mixture comprising one or more cation precursors, one or more anion precursors, and one or more amines to a ligand mixture including one or more acids, one or more phenol compounds, and a solvent to form a reaction mixture, wherein the molar ratio of (the one or more phenol compounds plus the one or more acids plus the one or more amine compounds) to the one or more cations initially included in the reaction mixture is greater than or equal to about 6, and heating the reaction mixture at a temperature and for a period of time sufficient to produce semiconductor nanocrystals having a predetermined composition. Methods for forming a buffer layer and/or an overcoating layer thereover are also disclosed. Semiconductor nanocrystals and compositions including semiconductor nanocrystals of the invention are also disclosed. In certain embodiments, a semiconductor nanocrystal includes one or more Group IIIA and one or more Group VA elements.
1. A method for preparing semiconductor nanocrystals, the method comprising:
adding a precursor mixture comprising one or more cation precursors, one or more anion precursors, and one or more amine compounds, wherein at least one cation precursor comprises a Group III cation precursor and at least one anion precursor comprises a Group V anion precursor, to a ligand mixture including one or more acids, one or more phenol compounds, and a solvent to form a reaction mixture, wherein the molar ratio of (the one or more phenol compounds plus the one or more acids plus the one or more amine compounds) to the one or more cations initially included in the reaction mixture is greater than or equal to about 6, and
heating the reaction mixture at a temperature and for a period of time sufficient to produce semiconductor nanocrystals having a predetermined composition, wherein the semiconductor nanocrystals include ligands attached thereto, wherein the ligands are derived from the one or more acids, the one or more phenol compounds, and the one or more amine compounds included in the reaction mixture.
2. A method in accordance with claim 1 wherein the one or more phenol compounds comprise a monocyclic phenol or a polycyclic phenol.
3. A method in accordance with claim 1 wherein the precursor mixture is prepared without heating.
4. A method in accordance with claim 1 wherein the precursor mixture further includes a precursor mixture solvent.
5. A method in accordance with claim 1 wherein the one or more acids comprise a carboxylic acid compound.
6. A method in accordance with claim 1 wherein the molar ratio of (the one or more phenol compounds plus the one or more acids plus the one or more amine compounds) to the one or more cations is greater than about 10.
7. A method in accordance with claim 1 wherein the molar ratio of (the one or more phenol compounds plus the one or more acids plus the one or more amine compounds) to the one or more cations is in a range from about 6 to about 20.
8. A method in accordance with claim 5 wherein the carboxylic acid compound comprises CH 3 (CH 2 )—C(O)OH wherein n=1-18.
9. A method in accordance with claim 5 wherein the carboxylic acid compound further comprises one or more aromatic groups.
10. A method in accordance with claim 1 wherein at least one of the one or more phenol compounds comprises a mixture of two or more different phenol compounds.
11. A method in accordance with claim 1 wherein the reaction mixture temperature is in a range from about 150° C. to about 300° C.
12. A method in accordance with claim 1 further comprising isolating the nanocrystals from the reaction mixture.
13. A method in accordance with claim 1 wherein the semiconductor nanocrystals comprise semiconductor nanocrystals that are capable of emitting light with a peak emission wavelength in a range from about 800 nm to about 2 microns upon excitation.
14. A method in accordance with claim 1 further comprising:
forming a buffer layer comprising a second semiconductor material over a portion of the outer surface of the semiconductor nanocrystals.
15. A method in accordance with claim 14 wherein forming the buffer layer comprises adjusting the temperature of the reaction mixture to a second temperature, separately adding one or more buffer anion precursors and one or more buffer cation precursors, and reacting the buffer precursors to form the second semiconductor material.
16. A method in accordance with claim 14 wherein the semiconductor nanocrystals are isolated from the reaction mixture prior to forming the buffer layer.
17. A method in accordance with claim 14 wherein the second semiconductor material comprises a II-VI semiconductor material.
18. A method in accordance with claim 1 further comprising:
forming an overcoating layer over the outer surface of the semiconductor nanocrystals.
19. A method in accordance with claim 18 wherein no additional acids, phenol compounds, or amine compounds are added in the overcoating step.
20. A method in accordance with claim 18 wherein the method further comprises:
forming a buffer layer comprising a second semiconductor material over a portion of the outer surface of the semiconductor nanocrystals prior to forming the overcoating layer.
21. A method in accordance with claim 1 wherein the molar ratio of cation to anion in the precursor mixture is greater than 1.
22. A method in accordance with claim 1 wherein the anion precursor comprises an ionic compound or a covalent compound that serves as a source for a Group V anion.